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PROFESSIONAL PAPERS OF THE ENGINEER DEPARTMENT, U.S. ARMY. 
No. 18. 


REPORT 


OF THE 


GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL 


MADE 


BY ORDER OF THE SECRETARY OF WAR ACCORDING TO ACTS OF 
CONGRESS OF MARCH 2, 1867, AND MARCH 3, 1869, 


UNDER THE DIRECTION OF 


BRIG. AND BVT. MAJOR GENERAL A. A. HUMPHREYS, 


CHIEF OF ENGINEERS, 


BY 


CLARENCE KING, 


U. 8. GEOLOGIST.? 


ote 


. 


VOLUME I. 


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UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL, 
CLARENCE KING, GEOLOGIST-IN-CHARGE. 


SYSTEMATIC GEOLOGY 


BY 


CLARENCE KING 


U. 8S. GEOLOGIST. 


SUBMITTED TO THE CHIEF OF ENGINEERS AND PUBLISHED BY ORDER OF THE SECRETARY OF 
WAR UNDER AUTHORITY OF CONGRESS. 


ILLUSTRATED BY XXVIII PLATES AND XII ANALYTICAL GEOLOGICAL MAPS, AND 
ACCOMPANIED BY A GEOLOGICAL AND TOPOGRAPHICAL ATLAS. 


P WASHINGTON: 
GOVERNMENT PRINTING OFFIOK. 
1878. 


V-VI 


ey Me 
{ 4 “a A ke 
Ve) Géiorer 


LABr En On CONDENS: 


ENTRODUOTORY LETTER ..2-s.<scscecessoseae Baten Hone 


CHAPTER I. AREA AND EXPLORATION OF FORTIETH PARALLEL........... 


CHAPTER IT. ARCH AAN. 
Section I. 

II. 

Il. 

IV. 


CHAPTER III. PALAozoIc. 


SECTION I. 


CHAPTER IV. MESOZOIC. 
Section I. 
IN 
TATE 
CHAPTER VY. CENOZOIC. 
SECTION I. 
iis 
100, 
IV. 
Vv. 


CHAPTER VI. RESUME OF STRATIGRAPHICAL GEOLOGY.... 


CHAPTER VII. TERTIARY VOLCANIC ROCKS. 


Section I. 
IDG 

Iie 

IV. 

Vis 

AE 


WALI: 


CHAPTER VIII. OROGRAPHY 


ARCHAGAN HXPOSURES).-.-2. 220+. 50 S00C CBSO OSE 
CORRELATION OF ARCHAIAN ROCKS ..........-.- 
GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 
PRE-CAMBRIAN TOPOGRAPHY ......... waoudoses5 6 
PATO ZOIGME xP OSURESHReE entero cances ior ssvets 
RECAPITULATION OF PALMOZOIC SERIES......... 
UW UNS) gonouaise Gocecoc sdo006 mises Bee CORSAGE 
JURASSIC ......- Roteretere Bootie HOORSG AOE panenepee 
CEELDACHKOUSHeeeeoeremen cere Weasel ietmiscieyas aie 
EQCENE) CERTIARY.>-ceeeeeo alot iets ote c/a, wialecwawy 
MIOCENE TERTIARY..-.-...... aye clare erento sey ee iererere 
IPETOCENE DER DIAR? a eis eeleeieie ceciceere samara ss 
RECAPITULATION OF TERTIARY LAKES..........- 
QUATERNARY .....- erhecesee Spe odes Bt etaiora Sai arcane 
PROPYLIDES se. +e Son oo ecRaocuosade Seteieieleket tee 
TASNID ESTEE Sprereteyyoyereteistelere Siajeiselsucerereiee eistaiesisvens Sere 

TRACHYTES..... ei ayowrsin Blele ciety akeree ye Serotiteicine a cle:s 
REYOLITES! <2. 1c scieciee = waroeteramererets etepenee ey eia.tic 
ESAS TAME DS Says tet melt iter siecloteronersiats Bese tantarate hess ae 


CORRELATION AND SUCCESSION OF TERTIARY VOL- 
CANIC Rocks 
FUusIoN, GENESIS, AND CLASSIFICATION OF VOL- 
CANIC Rocks 


wI4\> 


VIII TABLE OF CONTENTS. 


Page. 
APPENDIX BY J. T. GARDNER ON GEODETICAL AND TOPOGRAPHICAL . 
MR PHODS er ereretetereterecshe le eiaiatetetereratclars cieiaiarciaraioteseremieteie reine mya is eravaletere aie che stare 762 
1 G00) 0), CoRR Pace aan Wi eletar. e eee yer ee mG e HONS Ee AA AOE Teil 
TABLES OF CHEMICAL ANALYSES. 

I. ARCHZAN METAMORPHIC ROCKS...... -. -- Raver bale ae eels mm aeiee oer inhl 
TEAR CHATAN PE RUPTEVE) GRANTDES ccc ceteciciecin creas cieleleiciaeieioieislsleleaielotele 111 
III. DEsiccATION-PRODUCTS OF LAKE BONNEVILLE........ elseistee eaeioeiee 502 
EV SALINE AND HOT-SPRING ERODUOTS jes scl «soi isteinleleveleliviay= sole) aleletsic lalate 503 
V. DESICCATION-PRODUCTS OF LAKE LAHONTAN ....-....2.--.ceesee- ee 528 
VI. A.-B. SEDIMENTARY ROCKS, LIMESTONES......---. -- 2+ eeee sees ceee ee 543 

VII. A.-B. SEDIMENTARY ROCKS, QUARTZITES AND SANDSTONES.........-. 543 
VIII. PROPYLITES AND QUARTZ-PROPYLITES........--2- +200 e---00 eee eee 560 
EX. ANDESITES AND DAGITNS seem ec cerecce ctelecccesiciee sa elcee eee eee ame 

OX CAN = SS RAC He IGS epee rete terete er seat telco alot <telaloiieitetalclcioiel steleteiolelelel-latwieta telat 604 

Xe IRAUVOLITES seen ieeeterslele crelete leslie e cles sleiels erstelel olaleiwietslaimintatetet= 652 
NONE VV eH aS conc oso nde ce ose oe deas boadoU besODU dda sbooodn Bre pysrscicieeictercre 676 


XT. DIABASES AND SDIORITES tsleiccicislcicls sie .c\e.e<)= elaletclefeleieieisicieisicietersiate slave cievatee 676 


LIST OF ILLUSTRATIONS. 


All the illustrations of this volume were executed by Julius Bien, the chromo- 
lithographs after studies by Gilbert Munger, plates in black after photographs by 


T. H. O'Sullivan. 
FRONTISPIECE—Natural Column, Washakie Bad-Lands ...--.--..--- facing title-page. 
PROFILES of Ranges, Fortieth Parallel Area .......---..--.------ facing page 14 
PuatTE I. Heights of the Wahsatch....--..--------.------ aoowooous dozer 44 
II. Lake Marian, Humboldt Range, Nevada.....- ...-..-.--- dossee 64 
Ill. Archzean Quartzite, Humboldt Range, Nevada..-.-.....--- domeane 70 
IV. Glacial Cation in Archean Summit, Humboldt Range....-. Gls 56e 66 
V. Cation of Lodore, Uinta Range, Colorado.......----.----- doves 148 
VI. Yampa Caiion, Uinta Range, Utah ......-----..--------- do.-.. 44 
VII. Upper Valley of Bear River, Uinta Range, Utah.....-.-.-. doves.) Loz 
VIII. Lake Lal and Mount Agassiz, Uinta Range, Utah..-.-....- do.... 154 
IX. Mount Agassiz, Uinta Range, Utah.....--.--..--- pains cas do.... 156 
X. Provo Falls, Wahsatch Range, Utah .--.-.-.---.--------- do.. 172 
XI. Cation in Wahsatch Limestone, Humboldt Range, Nevada...do.... 204 
XII. Devil’s Slide, Weber Cafion, Utah..........-.-.----.------ WWOgs56 2H 
XIII. Eocene Bluffs, Green River, Wyoming ..-.-.------. .----: doz. 308 
XIV. Eocene Bluffs, Green River, Wyoming .-.-...----.------- do ..- 390 
XV. Washakie Bad-Lands, Wyoming....-..-...--------------- dos... .396 
XVI. Shoshone Falls, Idaho .......----...------------+----- Pa nCOseee | O90 
XVII. Shoshone Falls, Idaho, from below ......-.----..------+-: GWac5o Ue 
XVIII. Shoshone Falls, Idaho, from above.........---.--- -.---- dOis..- 594 
XIX. Snake River Caiion, Idaho ......-....--.---------+------ doz... 596 
XX. Rhyolite, Pah-Ute Range........-..-----.-----------+--- do.... 640 
XXI. Rhyolite Columns, Karnak, Montezuma Range, Nevada --edo.... 644 
XXII. Wahsatch Range, from Salt Lake City, Utah....-...-..--- dow... 492 
XXIII. Pyramid and Tufa Domes, Pyramid Lake, Nevada. .....--. do.... 514 
XXIV. Tufa bank, Anah6 Island, Pyramid Lake, Nevada .....---- doses. | O16 
NeXGVeN No tadotailshccee ecco eae ecee es wueeress C0... O18 
XXVI. Desert Lake, near Ragtown, Nevada....--.--.- ------- NdOLe-2) O12 


x LIST OF ILLUSTRATIONS. 
ANALYTICAL GEOLOGICAL MAPS. 
ieArchzan and Granitic Dxposures)- 22... sree aeeeteee facing page 
II. Archzan, Granitic, and Paleozoic Exposures.................-- donae- 
III. Pre-Mesozoic and Mesozoic Exposures .........--....-...s- -«- donee 
VAI Tertiany lx POSULCS = meeree eerste cic sie icet tateicleers elelelsisinie eteleieteisecins do -2- 
Vie Glaciors’ of the lcerA oe wesw careers letatajoebe sie iareve nie syelenerereteraimiere dosees 
Wile ualcestofathei Glacial eriodeeeesetaetotee oiietekelst=eleerat-l eee eee dopece 
Wald Rertiarys ViolcanlCaROck Spas citerieciieicl= = aeieliels\stcrele) aie stevov = sieter oper doy se 
VIII. Exposures of successive Orographic Disturbances. .........-.-- dOsa=5 
IX. Exposures of successive Orographic Disturbances ......-..-.-- soot Woet 
X. Exposures of successive Orographic Disturbances......-.....-.. dosa=- 
XI. Exposures of successive Orographic Disturbances......- BC GIAC dozece 
XII. Exposures of successive Orographic Disturbances .........  ...-do-.... 


OFFICE OF THE UNITED STATES GEOLOGICAL 
EXPLORATION OF THE ForTIETH PARALLEL, 
23 Fifth Avenue, New York, March, 1878. 


GerNeERAL: I have the honor herewith to transmit Volume I. of the 
Report of this Exploration. Its subject is SysremaTic GEOLOGY OF THE 
FortietH PARALLEL. 

The field-facts here assembled were observed by Arnold Hague, 8. F. 
Emmons, and myself. All inductions are my own. Determinations of 
invertebrate fossils were made by the late Prof. F. B. Meek, or by Messrs. 
Hall and Whitfield. Purely microscopical details in the chapters on Crys- 
talline Rocks are derived from Volume VI. of this series, and are thus 
credited to Prof. Ferdinand Zirkel. 

The method of this volume is historical. It is an attempt to read the 
geology of the Middle Cordilleras, and to present the leading outlines of 
one of the most impressive sections of the earth’s surface-film. 

For the freedom of action you have always granted me, for your 
generous bestowal of every needed facility, and above all for your wise and 
just guidance of the general plans of the work, I beg to offer my warmest 
thanks. 

That which a student of geology most earnestly longs for, I have freely 
received at your hands, and whatever value this Report may possess, either 
as a permanent contribution to knowledge or as a stepping-stone worthy 
to be built into the great stairway of science, I feel that the honor belongs 
first to you. 

I’or those who are to continue the arduous labor of American field- 
study, I can wish no happier fortune than to serve within the department 
which you command. 

Very respectfully, your obedient servant, 
CLARENCE KING, 
Geologist-in- Charge. 
To Brig. Gen. A. A. Humpnreys, 
Chief of Engineers, U. S. Army. 


xi-xli 


CHAPTER I. 
AREA AND EXPLORATION OF FORTIETH PARALLEL. 


The Exploration of the Fortieth Parallel promised, first, a study and 
description of all the natural resources of the mountain country near the 
Union and Central Pacific railroads; secondly, the completion of a continu- 
ous geological section across the widest expansion of the great Cordilleran 
Mountain System. 

In 1867, when the Fortieth Parallel Corps took the field, there was no 
authentic map which displayed the continuous topography from California 
to the Great Plains. The labors of several military explorers—among 
whom were Frémont, Stansbury, and Simpson, of the Corps of Kngi- 
neers, and Bonneville, Lander, Beckwith, and Gunnison—had lifted our 
knowledge of the Fortieth Parallel country out of the condition of myths, 
and had fixed with commendable accuracy the geographical positions of 
many of the most important natural objects. Major Williamson, also of 
the Engineer Corps, had lately made a reconnoissance through northwestern 
Nevada, adding a valuable map of the lowlands lying near the California 
boundary. With all this, there were still serious gaps in our topographical 
knowledge, not only as to orographical details, but concerning the position 
and area of considerable mountain masses. 

A general geographical sketch map of the Cordilleras of the United 
States, the preliminary sheet of the Atlas accompanying this report, shows 

1k 


2 SYSTEMATIC GEOLOGY. 


the area covered by this Exploration, and indicates the special division into 
blocks corresponding to the maps of the series. It will be seen by refer- 
ence to this sheet that the Exploration has covered a belt of country one 
hundred miles wide from north to south, extended from the meridian of 
104° west, in a direction a little south of west, as far as longitude 120° 
west, partly enclosing the 40th parallel, but near the eastern extremity of 
the work deviating a little to the north of the line. This departure from 
the parallel was necessary in order to embrace the most northerly curves 
of the Union Pacific Railroad without increasing the hundred-mile width 
of the belt. It was further desirable because the resultant direction of the 
belt of exploration approached more nearly a perpendicular to the general 
trend of the Cordilleran system. Alike for the purposes of illustrating the 
leading natural resources of the country contiguous to the railroad and for 
purely scientific research, the belt was made one hundred miles wide from 
north to south. ‘Though simple in its leading outlines, the structure of the 
Cordillera is in detail a labyrinth of intricate changes. One well observed 
section traced across a single range or a complex chain, or even through 
the whole broad system, would in most cases simply mislead the student. 
A parallel section five miles either side of it might result in a totally differ- 
ent reading. It is believed that this work, covering as it does a broad belt- 
section, has avoided the danger of insufficient or ambiguous evidence, and 
that the geological conclusions offered in this volume are safe. 

The State Geological Survey of California had carried its bold explora- 
tions throughout the Sierra Nevada and Coast ranges, bringing to light 
the most stupendous exhibition of geological effects on this continent. 
Professor Whitney, not to be cut off by the political boundaries of his 
State, had pushed private investigations over much of the Pacific slope. 
Warren, Hayden, and others had undertaken the questions offered by the 
Great Plains. Between California on the west and the eastern base of the 
Rocky Mountains was a broad gap of 16° longitude, in which our geo- 
logical knowledge was merely fragmentary and amounted practically to 
nothing, since it was all comprised in the notes of a few valuable and inter- 
esting localities of fossils, without the slightest data for correlation of hori- 
zons or the most shadowy outlines for stratigraphy. 


AREA AND EXPLORATION. 3 


With the help of an ardent and untiring corps, I have endeavored to 
work out the continuous geology across this gap, making adequate connec- 
tions with the territory surveyed by Whitney on the one hand, and with 
Hayden’s field on the other. Having completed this, I am now able to 
offer a comprehensive view of the broadest expansicn of the great American 
mountain system, and to present in some detail a section of sufficient mag- — 
nitude to render approachable some of the extended problems of mountain 
dynamics. 

It has rarely fallen to the lot of one set of observers to become inti- 
mate with so wide a range of horizons and products. Embracing within 
its area a pretty full exposure of the earth’s crust from nearly the greatest 
known depths up through a section of 125,000 feet, taking in all the 
broader divisions of geological time—a section which has been subjected to 
a great sequence of mechanical violence, and can hardly fail to become 
classic for its display of the products of eruption—this Exploration has 
actually covered an epitome of geological history. 

The purpose of this volume is to present, as briefly as possible, a sys- 
tematic statement of the data collected and the inductions we have been 
able to make. In Volume II. will be found a continuous description of the 
geological facts observed, treated geographically, beginning at the eastern 
extremity of the explored area and progressing westward, range by range, 
valley by valley, to the California boundary-line. Whoever wishes to know 
the structure and details of given features should consult that volume. In 
these chapters the method of treatment adopted is, to begin at the bottom 
of the geological column and present all the important facts we have accu- 
mulated on each successive formation, always attempting to correlate the 
wide-spread data and construct a continuous piece of geological history. 
Elements of difference and points of identity with other fields cannot fail to 
compel the reader, as they have the writer, to institute a constant mental 
comparison with localities and modes of geological action outside the area. 
In the interest of compactness, however, such comparisons have been nearly 
always omitted here. Presenting thus the fullest range of horizons, the 
arrangement of the book is chronological, beginning with the deposits of 
Archean time and proceeding without break through the Quaternary. 


4 SYSTEMATIC GEOLOGY. : 


Three classes of considerations are put forth: 1. Descriptions of geo- 
logical facts. 2. The direct correlation of facts into methodical grouping. 
3 Theoretical speculations. As far as possible, these are kept so sharply 
separated in independent chapters or sections, that the student will never 
be in doubt as to where actual observation stops and induction begins. He 
will be able to accept the facts as offered in the spirit in which they are 
given, as honest, unbiased, and approximately accurate, however his own 
logic may lead him to differ from my generalizations or speculations. | 

Readers are recommended to bear in mind that this work is not a geo- 
logical survey, but a rapid exploration of a very great area, in which liter- 
ally nothing but a few isolated details was before known. Unmapped, 
unstudied, it was terra incognita; and if in our difficult and arduous cam- 
paign we have done no more than outline the broader features of the geol- 
ogy, we have at least accomplished that, and have laid the foundation for 
those future slow and detailed surveys which we hope are sure to follow 
our pioneering labors. It has been my own share of the work to see as 
much of the field as possible, and to discover from the facts gathered by 
myself and my collaborators, Messrs. Arnold Hague and 8. F. Emmons, 
those unforced natural generalizations which come of bringing the field data 
into their just and logical apposition. The value, therefore, which it is 
hoped this volume may possess, lies mainly in its being a piece of connected 
history, in which the leading outlines are emphasized. 

In blocking out the explored territory into divisions suitable for atlas 
maps, it was found that the country naturally divided itself into five equal 
areas, each section covering a region having some independent characteris- 
tics. This natural division, as it came to be studied, proved in the main so 
desirable that it was finally adopted, notwithstanding that the boundary- 
lines do in some cases cut the geology rather unfortunately. 

The Atlas, besides the Cordillera Sketch Map already mentioned, cou- 
sists of duplicate series of geological and topographical sheets, on a scale of 
four miles to one inch, which, joined together on the proper projection-lines, 
form the continuous belt of work. Each area is shown first on a geological 
map based upon a portrayal of the mountain topography in grade curves 


of 300 feet vertical interval, the various formations appearing in their 


AREA AND EXPLORATION. 5 


appropriate colors. Accompanying this is a second map of the same region, 
the topography of which is lithographed in mountain shading with a side 
light. Added to these are two atlas sheets carrying two continuous geo- 
logical sections, drawn from actual observation, from east to west across 
the whole field of work. 

Before entering upon the chapters of detailed geology, I give here a 
succinct description of the more general characteristics of the five map-areas. 
The ‘greatest looseness prevails in regard to the nomenclature of all the 
general divisions of the western mountains. For the very system itself 
there is as yet only a partial acceptance of that general name, Cordilleras, 
which Humboldt applied to the whole series of chains that border the 
Pacific front of the two Americas. In current literature, geology being 
no exception, there is an unfortunate tendency to apply the name Rocky 
Mountains to the system at large. So loose and meaningless a name is bad 
enough when restricted to its legitimate region, the eastern bordering chain 
of the system, but when spread westward over the Great Basin and the 
Sierra Nevada, it is simply abominable. It is greatly to be hoped that the 
example of a few competent geographers and geologists who stand by Hum- 
boldt’s name will gradually come to be followed by all, and the term Rocky 
Mountains be confined to the east front of the Cordilleras. 

In this report and in the title of Atlas Map L, ‘“ Rocky Mountains” 
means that marginal chain which constitutes the eastern limit of the Cordil- 
leran system. It is made up of several dependent ranges, and its most 
important geographic function in the United States is, to divide the Missis- 
sippi Basin from the Pacific rivers. 

Map I. embraces a section of the Rocky Mountains consisting of a por- 
tion of Colorado Range extending from latitude 40° 20’ for a hundred miles 
due north; the northern extremity of Park Range, also a meridional body, 
lying about 30 miles west of Colorado Range; and a third range, having 
a northwest trend, and branching westward from Colorado Range, near the 
southern boundary of the map. ‘These three intimately related mountain 
masses are old Archean ranges, representing the earliest period of orograph- 
ical uplift of which there is any evidence in the Cordilleran ranges. They 


are all of topographical importance, from the great altitude of their summits 


6 SYSTEMATIC GEOLOGY. 


and their relation to the drainage-system. Park Range, the westernmost 
member of the chain, forms in our latitudes the Atlantic and Pacific 
watershed. 

The three ranges are based upon plateau country, from 5,000 to 7,000 
feet above sea-level. Passing west from the Missouri valley, the system of 
Great Plains rises from an altitude on the east of about 1,000 feet above 
sea-level, with remarkable gradualness, in one sweep up to the east base of 
Colorado Range, where against the foot-hills the elevation of the plains 
varies from 5,500 to 7,000 feet. Down the slope of this vast inclined plane 
the western tributaries of the Missouri and Mississippi flow, in rather shal- 
low valleys, edged often by abrupt bluffs. Near the mountains these valleys 
of erosion are sometimes 500 or 600 feet deep; but followed down their 
course they are seen to grow shallower and shallower, till the flanks of the 
depression roll away from the stream-bottoms in gentle undulations. 

The Plains geology, like the topography, is broad and simple, being 
composed of nearly level beds of Tertiary and Cretaceous age, tilted with 
the slight slope of the surface. 

Tree vegetation is confined to the immediate stream-banks, and even 
there, over the middle belt of plains, is almost wanting. Shrubs are equally 
rare with trees, the whole vast surface being covered with a growth of 
upland grasses. 

Seen from the east, Colorado Range presents a rugged front, deeply 
carved with cations, which deliver their streams through gateways in the 
foot-hills. The lower slopes are of dull, rusty colors, dotted with an occa- 
sional sparse growth of trees. Farther up, in the middle altitudes, a forest, 
composed of coniferous trees and aspens, flourishes in the cool, moist strata 
of upper air, and above rise the naked, snowy crags, broken and eroded 
into impressive peaks. The profile of the range shows a high, slightly 
serrated ridge entering the area of Map I. from the south, and terminating 
in Hague’s Peak, 13,832 feet high. Passing northward, the outline declines 
by long, sweeping curves to the region of the Union Pacific Railroad. 
North of that point there is only scattered forest, and the range to the 
northern limit of the map is little more than a block of undulating highland, 


with a few noticeable peaks. 


AREA AND EXPLORATION. 7 


Medicine Bow Range has even a more diversified profile, owing to 
prominent peaks, of which the highest is Clark’s Peak, 13,167 feet. The 
next most important, Medicine Peak, reaches 12,231 feet, and Elk Moun- 
tain, near the northern termination, 11,511 feet. Between these three high 
summits are deep ‘‘saddles” covered with coniferous forest. 

Park Range, like Colorado Range, enters the map in a meridional direc- 
tion, defined as a high, nearly level-topped ridge, presenting a sharp mural 
face to the east. Its highest peak, Mount Zirkel, is 12,126 feet. 

In the angle included between Colorado and Medicine Bow ranges is 
a fine, level area, which under the name of Laramie Plains sweeps north- 
ward many miles beyond our northern boundary. Its general altitude is 
7,000 feet. It is drained by Laramie River. 

In the depression between Medicine Bow and Park ranges is the oval 
basin of North Park, another gently undulating plain. The waters of the 
North Platte, which drain northwestward through the Park, continue 100 
miles farther in the same direction, occupying the bottom of a broad valley 
which partakes somewhat of the character of the grass plains, and yet shows 
the influence of the more desert conditions of the country to the west. 

In general, this Rocky Mountain region is one of heavy ranges, well 
forest-covered in the elevated regions, and dominated by fine peaks which 
bear perpetual snow. Around and between the ranges are gently undulat- 
ing or wholly level plains clad with upland grasses. The region embraces 
heights from 5,000 to 13,832 feet above sea-level. As a whole, it is a high- 
land from which the great plains decline to the east, bearing on their sur- 
face the Mississippi rivers, and sloping gently off westward into the Green 
River Basin, the declivity in that direction carrying the tributaries of the 
Pacific River Colorado. There is no desert over the whole highland, but 
toward the west the vegetation begins to be mingled with the characteristic 
Artemisia of the arid basin of the Colorado. Over this area is a sky of 
liquid but cold blue, singularly vaporless for many weeks of the year. 
Clouds, when they come, gather around the mountain summits or drift over 
the plain at low elevations, sailing against the hill-slopes to break up and 
dissolve in the dry air. In the aspect of the country the most conspicuous 
features are, the pale tone of the plains—light golden green in summer, 


8 SYSTEMATIC GEOLOGY. 


russet in autumn, and white in winter; the deep blue green of the forest- 
covered heights always in view, looming over a plain; and, perhaps most 
characteristic of all, the cool but dazzling brilliance of the sunlight. 

Map IL., a section of the Green River Basin, represents a very different 
set of conditions. A chain of east-and-west mountain elevations, made up 
of Uinta Range and its easterly dependencies, is traced across the gen- 
eral basin of Colorado River, dividing it into two distinct provinces. The 
region north of the Uinta represents an upper series of depressions, taking 
the name Green River Basin from the main river, whose various tributaries 
carry off the complicated drainage. South of the Uinta system lies the 
great plateau basin of the Colorado, one of the most extraordinary geo- 
eraphical features of the globe. 

The area shown upon Map IL. is a section across the southern portion 
of the Green River Basin, including the Uinta system, which bounds the 
Basin on the south, and the western highlands, in which Wahsatch Range 
forms the western boundary of the depression. 

The general configuration of the Green River area is that of a rude 
triangle, having the Uinta system as the base, the Wahsatch as the western 
side, and the great Wind River Range, with the westward members of the 
Rocky Mountain chain, as its eastern boundary. From north to south the 
level extent is about 150 miles, with an equal distance along the southern 
margin of the basin. Viewed as a whole, it is a broad area of desert plains, 
slightly varied by local ridges and the mural escarpments of horizontal 
Tertiary tables. These lesser details are not of sufficient dimensions to 
change the prevailing character of the rolling plain. Along the middle 
is the north-and-south line of the greatest depression occupied by the 
winding bottom of Green River. The rise from the river to the extreme 
limits of the basin east and west is only about 1,000 feet. The lowest alti- 
tudes are 5,500 feet. The character of these plains differs widely from the 
grassy upland levels of the Rocky Mountain system. It is essentially a 
desert, bearing upon its surface even less vegetation than the Great Basin. 
The prevailing desert colors are yellowish-gray, red, and ashen hues, derived 
from the disintegrated material of the soft, fresh-water Tertiary strata whose 


comparatively level beds are the groundwork of the country. 


AREA AND EXPLORATION. 9 


Among the most interesting topographical and geological features of 
the desert levels are the so-called Bad Lands, which are essentially escarp- 
ments of the edges of Tertiary tables, varying from 200 to 600 or 700 feet 
in height, and carved by meteoric agencies into fantastic and architectural 
forms. They occur both east and west of Green River, in the basins of 
Bridger and Washakie, and are developed on a remarkable scale. Those 
of Washakie are found on the southern face of a long escarpment varying 
from 200 to 400 feet in height. The soft level marls and sands of the 
Eocene are sculptured into innumerable turrets, isolated towers, and citadel- 
like masses, which, when seen at a little distance, present the aspect of a 
great walled city, with outlying bastions and buttresses, and lines of level 
buildings along the crest of the wall. The Bad Lands are characterized 
by an almost entire absence of vegetation. A few Artemisias and other 
stunted desert shrubs grow at rare intervals upon the plains and upon the 
tops of the mesas, but the sculptured fronts are quite devoid of any plant 
life. The very soft gray, clay faces of the abrupt walls show the level 
edges of strata, which add to the architectural effect the appearance of a 
gigantic masonry. 

Toward the east and the west, where the basin rises in the region of 
its bounding mountain masses, the Tertiary plains rise by a series of gently 
graded steps or soft inclined planes; so that, in approaching one of the 
mountain ranges from the deserts, the green, forest-covered uplands are 
seen rising in a sharply defined ridge above the level surfaces of the 'Ter- 
tiary table-lands. 

Within the limits of Map IL. the only one of the great bounding 
mountain ranges that encompass the Green River Basin is Uinta Range, 
which forms the southern barrier to the basin. It is an immense single 
mountain block, about 150 miles long, having an average elevation of 
10,000 to 11,000 feet, and rising at its culminating point, Emmons’s Peak, 
to 13,694 feet. It is defined, both on the north and on the south, by 
Tertiary table-lands, which abut unconformably against its steeply inclined 
strata. As a range it is unlike any other in America, being in fact a great, 
lofty plateau of nearly horizontal strata, which at the north and south 
edges are sharply broken and thrown into highly inclined positions. The 


10 SYSTEMATIC GEOLOGY. 


physical and geological section, therefore, is of a great, flat anticlinal, having 
a plateau summit thirty or forty miles wide. The whole upper region, 
above 8,000 feet, is covered by a superb forest growth, chiefly made up 
of Pinus flevilis, P. ponderosa, Abies Menziesii, A. Engelmanni, A. Doug- 
lasi, A. grandis, and A. amabilis, together with Juniperus Virginiana on 
the lower levels. The upper plateau region is deeply carved, by the 
erosion of the glacial period, into a net-work of immense amphitheatres, 
opening downward into a series of great ice-worn canons. The resultant 
topography is that of an intricate series of narrow ridges and a great pro- 
cession of angular peaks, all carved out of horizontal beds. It is a type 
of mountain architecture only paralleled by the uplands of the Caucasus. 
Instead of the sharp, granitic needles, or contorted strata of most moun- 
tain-tops, the Uinta peaks show, all along their flanks and on the mural 
faces, the level, heavy bedding of the great quartzitic and sandstone forma- 
tion of the range. If the Bad Lands of the plains are architectural, the 
high peaks of the Uinta are in a different way quite as markedly imitative 
of masonry. Considerable banks of perpetual snow are found upon the 
shadowed slopes through the whole heights, and the view from one of 
the upper summits is varied by open, green Alpine pastures, varied by 
innumerable lakes of transparent water which occupy the erosion-hollows 
of the old glacier-beds. Here and there the amphitheatre walls and the 
lake surfaces of the high mountain basins are brilliantly glacier-polished. 
There is rarely in one region a more marked physical contrast than may 
be observed between the stretches of clay desert and Bad Land,—in which 
all the topographical features are subdued by the low vertical scale, where 
vegetation is wanting, and the whole tone of the landscape is ashen,—and 
the vast, rolling, wave-like ridges of the Uinta foot-hills sweeping up with 
their deep green covering of coniferous woods, surmounted by the lofty 
pyramidal summits whose dark-red strata are traced in level lines across 
all the surfaces that are lifted above the plane of vegetation. 

Passing westward, and rising to the highlands which bound the Green 
River Basin in that direction, a gradual change is noticed in the vegetation. 
The desert plants give way to grass, and the level Tertiary strata to inclined 


vidges of older rocks that crop sharply through them. The highland cul- 


AREA AND EXPLORATION. 11 


minates in the wall of Wahsatch Range, which forms a sharp division 
between the Tertiary plateau regions and the deep depression of the Great 
Basin to the west. The high region embraced by the Wahsatch and the 
‘plateaus around Weber River is deeply cut by canons of the drainage of 
Bear and Weber rivers, whose waters flow westward through gaps in the 
Wahsatch and are finally delivered into Great Salt Lake. 

The area of Map III. embraces the Wahsatch and a considerable part 
of the highland immediately east of it, which, taken together, form a great 
elevated bounding-mass overlooking the low plains of Salt Lake. Wahsatch 
Range, forming the west margin of the highland, is a marked topograph- 
ical feature, and for geological interest is certainly second to no single 
mountain block in the world. The range itself is really a great mountain 
wall, the result of a profound break in the earth’s crust; the western half of 
the range has been carried down beneath the level of the present plains, 
leaving a lofty face presented to the west. This mural escarpment has 
been carved down by numerous deep canons, leaving the summit of the 
wall in the form of a series of sharp, towering peaks. It is really the 
edge of the plateau system to the east, although its higher summits are 
lifted several thousand feet above the level of the horizontal Tertiary strata 
which sweep up toward it from the east. Erosion has also dug out a series 
of canons parallel to the front of the range, along its eastern side, defining 
it somewhat from the Tertiary table-land. The heights of the range are 
sparsely wooded, considerable coniferous groves gather on the cooler 
mountain shoulders of the highest group south of Salt Lake, and a few 
inconsiderable bodies of forest are seen along the summits, as far as the 
northern extremity of the map. From the valley of Salt Lake, the highest 
peaks rise between 8,000 and 9,000 feet. The average elevation of the 
entire wall is not less than 4,000 feet above its base. 

Far more than Uinta Range, the Wahsatch partakes of the desert 
character of the low country to the west. Along the west base of the range 
lie the plains of Salt Lake and the valley of the Jordan, whose level does 
not vary far from 4,200 feet above the sea. These lowlands stretch west- 
ward for nearly a hundred miles, forming a great connected series of deserts, 
all the lowest portion of which is occupied by Great Salt Lake. 


12 SYSTEMATIO GEOLOGY. 


Along the south and west sides of the lake, the streams of the Wah- 
satch furnish a natural irrigation which has been turned to good account 
by the Mormon settlers, producing a margin of green farms and meadow 
lands that slope nearly or quite to the margin of Salt Lake; but to the 
southwest, west, and north, the plains come to the brink of the lake as arid, 
level deserts, covered more or less by saline efflorescences, and unbroken 
save by bare mountain ridges of nearly naked rock, which rise like islands 
out of the glistening alkali desert. Along the base of the Wahsatch, 
around the various islands of the lake, and equally about the island- 
like mountain masses that rise from the neighboring deserts, are traced a 
series of horizontal lake-terraces, the highest of which are about a thou- 
sand feet above the present level of the lake. This wonderful and con- 
spicuous feature arrests the attention of all travellers, and is readily seen to 
mark the ancient level of an extinct lake. In fact, the whole basin of 
Utah is, as will hereafter be described, simply the dry bed of a very great 
early Quaternary lake, to which G. K. Gilbert has given the name of Lake 
Bonneville. 

Salt Lake itself, having no outlet, and receiving the influx of Jordan, 
Weber, and Bear rivers, besides several unimportant Wahsatch streams, 
rises and falls with every climatic fluctuation, and the density of its saline 
solution varies constantly, being inversely proportionate to the volume of 
water. 

The area of Map IV. comprises the plateau of central Nevada, and lies 
between the basin of Utah, or the Great Salt Lake desert, on the one side, 
and a strikingly similar desert lowland on the west. It is a region whose 
valley plains vary from 5,000 to 7,000 feet in altitude, and whose most 
prominent topographical feature is the great series of approximately par- 
allel mountain ranges which are traced from north to south over the whole 
plateau. The most lofty and considerable of these ranges, near the middle 
of the plateau, is Humboldt Range, a bold, rugged mass of Archzan and 
Paleozoic rocks, rising to elevations above 12,000 feet, and lifting fully 6,000 
feet above its base. The mountain ranges of the plateau are, for the most 
part, extremely barren. They are characterized by the unusual predomi- 


nance of naked rocks and the almost complete absence of forest. The lon- 


AREA AND EXPLORATION. 113} 


_ gitudinal valleys that separate these isolated mountain ranges are generally 
covered with a strong growth of desert shrubs, and here and there along the 
lines of drainage, or about some small lake, are refreshed by limited pas- 
sages of green vegetation. The climate is essentially that of a desert, sub- 
ject to very great extremes of temperature, in spite of which vegetation 
flourishes remarkably in the presence of artificial irrigation. The long, 
winding valley of the Humboldt, which descends from the middle of the 
Nevada plateau westward to the depressed basin of Nevada, offers facilities 
for the irrigation of a considerable amount of land, and here the grain and 
grass crops are seen to be remarkably luxuriant. Wherever, in the whole 
plateau, a mountain stream has sufficient force to flow out into the valleys, 
cultivation is repaid by an extraordinarily rapid and fine growth of farm 
products. ‘Throughout the high mountains, near the summits, especially in 
the neighborhood of any regions of crystalline rocks, there are abundant 
springs and fine mountain brooklets ; but before they reach the lowlands 
they are drunk up by the parched earth or all evaporated 

The area of Map V. shows a section of the basin of Nevada, where it 
descends by gentle steps from the central Nevada plateau. Here, as in the 
Great Salt Lake desert, are immense stretches of level plains of sand and 
alkaline clays, carrying the saline lakes which gather in the lowest basins. 
Here, again, is the bottom of a large extinct lake of the Quaternary period, 
contemporaneous and equally extensive with Lake Bonneville. This great 
extinct sheet of water we have named Lake Lahontan, in honor of the 
explorer. Although the area of the residual saline lakes is entirely inferior 
to that of Great Salt Lake, the detached sheets of brackish water which are 
fed by Humboldt, Truckee, and Carson rivers are of very great picturesque 
and scientific interest. The basin of Nevada is ribbed by several barren 
mountain ranges, treeless and naked, displaying the brilliant and bizarre 
colors of countless outbursts of Tertiary voleanic rocks. The aspect of th’s 
desert differs greatly from that of Salt Lake in the elements of bright color. 
The dull, ashen deserts, margined with terraces covered with desert vegetation 
are interrupted by the tumultuous piles of red, yellow, white, pink, green, 
black, and gray rocks which form the irregularly disposed mountain masses. 

The area of this exploration ends with the 120th meridian, or the 


14. SYSTEMATIC GEOLOGY. 


boundary of California. Immediately beyond is the high eastern face of 
Sierra Nevada Range, bounding the Great Basin in that direction. It will 
be seen that the Great Basin, as a whole, consists of two great mountain 
walls, their steep sides facing each other, about 500 miles apart. At the 
bases of each lie low, desert plains, into which flow considerable rivers, 
only to pour into shallow alkaline lakes, which have no outlet. Between 
the two basins is a central plateau, highest in the middle and declining in 
both directions, like the roof of a house, to the desert lowlands. 

Appended to this chapter is a diagram of the longitudinal profiles of 
all the ranges shown on the Fortieth Parallel maps, from which the reader 
can obtain at a glance the relative altitude of summits and bases. 

Thus, in the most general way, I have traced the leading geographic 
features of the field of work. In the descriptive volume, No. Il. of this 
series, all the geographical details are treated with such fulness as to ren- 
der further particulars unnecessary here. 


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CHAPTER II. 
ARCH AAN. 


SEctTion I.—ARCHAAN EXPOSURES.—COLORADO RANGE—MEDICINE Bow RANGE— 
PARK RANGE—UINTA RANGE—WAHSATCH RANGE—SALT LAKE ISLANDS AND 
PROMONTORY—RAFT RIVER MOUNTAINS—DESERT GRANITE RANGE—GOOSE 
CREEK HILLS—OMBE RANGE—GOSIUTE RANGE—PEOQUOP RANGE—WACHOE 
MouNTAINS—KINSLEY DISTRICT—FRANKLIN BUTTES—HUMBOLDT RANGE— 
CoRTEZ RANGE—WAH-WEAH MOUNTAINS—SEETOYA RANGE—TOYABE RANGE— 
SHOSHONE RANGE—AUGUSTA MOUNTAINS—FISH CREEK MOUNTAINS—HAVAL- 
LAH RANGE— PAH-UTE RANGE— WEST HUMBOLDT RANGE — MONTEZUMA 
RANGE—PAH-TSON MOUNTAINS —PAH-SUPP MOUNTAINS—GRANITE RANGE— 
TRUCKEE RANGE—LAKE RANGE—PEAVINE MOUNTAIN—CALIFORNIA BORDER. 

SECTION II.—CORRELATION OF ARCHAAN Rocks.—METAMORPHIO Rocks— 
GRANITES. 

SECTION III.—GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 

SECTION [V.—PRE-CAMBRIAN TOPOGRAPHY. 


SECTION I. 
ARCHAAN EXPOSURES. 


Throughout the Cordilleran system in the western United States there 
is observed the usual distinct nonconformity between Archzean and subse- 
quent formations. At intervals over the whole mountainous area west of 
the 100th meridian, masses of gneiss or crystalline schists, with their asso- 
ciated marbles, dolomites, and quartzites, and eruptive bodies of granites, 
porphyries, gabbros, &c., are found to underlie more recent strata. These 
Archzean bodies are made to outcrop in three modes: 

First, the summits of Archzean mountain chains whose original elevation 
above the surrounding topography lifted them, if not over the level of sub- 


15 


16 SYSTEMATIC GEOLOGY. 


sequent ocean surfaces, at least above the plane of all subsequent deposition 
of detrital material. In spite of the powerfull:; accidented surfaces of Ar- 
cheean areas, and of the distinct and lofty chains whose existence I shall in 
the following pages endeavor to demonstrate, these primitive summits are 
the rarest of Archzean outcrops. That they should exist at all is rather to be 
wondered at, when we remember that a series of later rocks extending from 
the earliest Cambrian to the present period, and amounting in extreme cases 
to probably not less than 40,000 feet, has been superposed upon them, 
and that the region as a whole has been repeatedly subjected to some of 
the severest mechanical disturbances of which we have any knowledge. 
Yet such uncovered primitive summits do exist. 

Secondly, a type of occurrence due to local uplift or faulting, of less 
importance in a geographical sense than the last group. Archsean rocks 
are, indeed, here and there thrust through their younger covering; but 
these are limited blocks, the results of some severe local disturbance, crowded 
up to the surface or left upon the face of prominent fault walls, and although 
more frequent than original island summits, they constitute but a small part 
of the total exposure. 

Thirdly, the predominating type of outcrop is a result of erosion either 
upon the axial areas of later elevated mountain chains, or along their flanks, 
or in those deep river canons of which the system of the Colorado offers the 
strongest example. 

At present we have no conclusive proof of metamorphism of Paleozoic 
strata to so extreme a point as to endanger a mistake between the resultant 
rocks and those of Archean age. 

So far, unless in California, the Palzeozoic sedimentary series have only 
yielded limestones, quartzites, and slates, whose observed alteration-products 
do not in the least resemble Archzean forms. Perplexities like those in the 
Appalachian system are not yet brought to light; and the Archzean rocks 
themselves, as now known, present but a limited number of species. As a 
general result of this wide-spread petrological simplicity of areas, and the 
comparatively unaltered condition of Palzozoic formations, the relations 
between the two are exceedingly plain. 

Details of the buried and partially exhumed Archzan continent must 


ARCHASAN EXPOSURES. 17 


be accumulated very slowly; but there is still ample room in the remaining 
unexplored regions of the Cordilleras to find new features and perhaps to 
present many exceptions to the general laws which the writer is about to 
deduce from present data. 

Cororavo Rancr.—That part of Colorado Range lying within the limits 
of the Fortieth Parallel Exploration, as shown upon Map L, is comprised 
between latitudes 40° 15’ and 42°. At the northern extremity of the 
map the range consists of low rolling hills, having a breadth from east to 
west of about fourteen miles. This width is maintained, with slight varia- 
tions, down to the region of the railroad, where the range rapidly widens 
upon its west side, until at the southern line of the map it has reached 
35 miles. North of the railroad, the physical characteristics are quite uni- 
form, the range consisting of a moderately rolling upland, with but few 
prominent summits, the drainage divide being carried very near the western 
edge. Streams which for the most part flow eastward have carved out 
shallow, rocky valleys. The whole uplift is little more than a rolling pla- 
teau, of which the greatest elevations are in the neighborhood of 2,500 feet 
above the plains at the east base. The highest summits are a little north 
of Cheyenne Pass, on the west side of the range, about in the latitude of 
Laramie City, where the broad, undulating crest reaches the altitude of 
9,077 feet. Northward, as far as the upper streams of the Chugwater, the 
average elevation of the plateau is between 7,500 and 8,000 feet, with peaks 
reaching 8,600 feet. Thence the plateau country falls off, but rises again in 
rugged, granite hills, just beyond the limit of the map. South of the rail- 
road, where the pass-summit reaches 8,242 feet, the line of greatest ele- 
vation, as well as the watershed, deviates from the meridional line in a 
southwesterly direction, continuing about 45 miles to Clark’s Peak, a high 
summit, which belongs more properly to Medicine Bow Range. ‘This divi- 
ding summit is a broad, gneiss plateau of rolling, forest-covered surface, 
unrelieved by any high peaks, and unaccidented by any deep canons. The 
eastward slope, drained by the various forks of the Cache la Poudre, 
partakes of this same undulating character as far southward as Monitor 
Peak, latitude 40° 45’. From this point a decided change in the configura- 
tion of the range takes place. Between the waters of the Cache la Poudre 


2K 


18 SYSTEMATIC GEOLOGY. 


and the Big Thompson, a lofty, confused group of peaks, rising constantly 
to the south, occupies the whole broad area between the Great Plains 
and the North Park. Hague’s Peak, latitude about 40° 30’, having an alti- 
tude of 13,832 feet, is the centre of a considerable area of drainage, from 
which flow northward the South or Main Fork of the Cache la Poudre, 
and southward and eastward, in deep canons, the Big Thompson. [rom 
Hague’s Peak, bold spurs slope to the south and southeast, down to the 
level of a picturesque basin in the mountains, known as Estes’ Park. The 
country also slopes westward into a depressed region, and rises again at 
Mount Richthofen. South of Estes’ Park, and south of the limit of the map, 
the summit culminates in Long’s Peak. 

In the northern part of the range, and indeed as far south as the head 
of the North Fork of the Cache la Poudre, 500 feet is the usual depth for 
canons, and in consequence they offer but shallow exposures of Archzean 
rocks; while south of that point, corresponding to the greatly increased ele- 
vation of the peaks and general magnitude of the topographical features, 
the canons also increase in depth, until between Monitor and Comanche 
peaks there is a depression of 3,500 feet, with an equal one on the upper 
waters of the Big Thompson, and the average drainage valleys of this 
region are not less than 800 feet between walls. Consequently it is in this 
part of the range that the best exposures of the Archzean rocks may be 
obtained. 

Regarding the Archzean exposure as one, it will be observed, by refer- 
ring to Map I, that owing to differences of upheaval, of original overlap, 
and of erosion, the relation between Archzean and later series varies from a 
contact at the lowest horizon of the Paleeozoie up to the most recent of Pli- 
ocene conglomerates. For about 36 miles on the east side of the range, 
beginning at the southern limit of the map, the contact-line is between 
the red strata of the Triassic series and the Archean. From that point, 
for about 40 miles northward, it is chiefly between Archzean and lower 
Palxeozoic, which throughout this whole distance have a steep easterly 
dip; thence northward to the extremity of the range the Tertiaries some- 
times overlie and entirely obscure the edges of the upturned Paleozoic 
and Mesozoic series, bringing the Pliocene conglomerates directly in con- 


ARCHAIAN EXPOSURES. 19 


tact with the Archean. In this northern part, heavy promontory-like 
masses of the Archean jut eastward from the main trend of the east base, 
throwing the upturned stratifeed rocks into sharp, complicated curves ; 
the dip of these sedimentary beds varying from about 16° in the south, to 
a vertical position along the northern slopes, and in some rare instances a 
reverse dip. On the other hand, the western limit of the northern half of 
the Archzean exposure is observed to be in contact with the lower part of 
the Palzeozoic series, which for the upper 55 or 60 miles of the map dip 
gently westward, with slight local disturbances. South of the railroad, at 
Harney’s Station, the Triassic series have advanced eastward, and overlap, 
obscuring the Carboniferous, and the trend of the line of contact between 
the Trias and the Archzean is to the southeast, occupying a position on the 
flanks of the southwest divide before described. 

From the region of Long’s Peak Medicine Bow range deviates from the 
north-and-south trend of the Colorado body, in a direction about north 30° 
west, extending 100 miles to Elk Mountain, after which it plunges beneath 
the Cretaceous formations of the Platte Plain. For about 30 miles from 
Long’s Peak it is essentially so united with Colorado Range as to be 
geographically inseparable ; but from Clark’s Peak to Elk Mountain it pre- 
serves a direction and a character quite its own. It varies in width from 
about 12 miles opposite the middle of North Park to 80 miles in the 
region of Marble Peak. Northwest of Clark’s Peak a high rugged ridge 
is maintained for 8 or 10 miles, but it then falls off to a low rolling 
pass, utilized by the road from Laramie River to North Park. he lead- 
ing characteristics of the country from Clark’s Peak northward are not 
unlike those of the northern part of Colorado Range. In passing north- 
ward the range gradually rises to a culminating point about latitude 41° 
20’, known as Medicine Peak, which reaches an altitude of 12,231 feet; 
but even here there is little of the rugged character usual at such heights, 
the canons all exhibiting comparatively broad and gentle flanks. Still 
farther northwest, in the region of Cherokee Butte, the later sedimentary 
rocks on both sides of the peak approach within two miles of each other, 
and the mass of Elk Mountain, a semicircular Archzean body, is entirely 
surrounded by later stratified rocks. The broad angle between Colorado 


20 SYSTEMATIC GEOLOGY. 


and Medicine Bow ranges is occupied by Laramie Plains, which con- 
sist chiefly of gently inclined Cretaceous strata, abutting nonconformably 
against the sloping foot-hills of the Archzan mass of Medicine Bow and 
overlying, along the eastern side of Laramie Plains, the Jurassic, ‘Triassic, 
and Paleozoic, which dip at gentle angles from Colorado Range. The 
west side of Medicine Bow Range sinks into the valley of the North Platte, 
whose great expansion south of latitude 40° 50’ is known as North Park. . 
With the exception of a fragment of Carboniferous and a few miles of 
Triassic, Jurassic, and lower Cretaceous strata, the whole western margin of 
Medicine Bow Range is covered with but slightly disturbed Tertiary beds. 
Near the southern extremity of the map the sedimentary margin of the 
range, as well as the edge of the Archiean core, is overflowed by a mass of 
rhyolite. It is therefore essentially an irregular, elongated body of Archaean 
rocks, having its flanks submerged beneath gently inclined Cretaceous and 
Tertiary series, with a few outcrops of the Paleozoic and the Mesozoic 
strata appearing at intervals under the more recent sedimentary series. 
West of North Park, and west also of the valley of the North 
Platte, lies the northern extremity of a bold wall of Archzean rocks, which 
extends southward for many miles and forms the western boundary of the 
series of Colorado parks. To this elevation Mr. James T. Gardner has 
applied the name of Park Range. About 70 miles of its northern end are 
embraced within Map I. ‘Topographically it may be considered as a north- 
and-south range as far north as Pelham Peak, from which point the main 
mass has a northwest trend approximately parallel to Medicine Bow Range. 
With the exception of a narrow strip of Triassic and Jurassic strata in the 
northern part of North Park, and a little Cretaceous against the middle of 
North Park, the whole eastern margin of this great Archean body is formed 
by overlying Tertiaries of North Park and Platte Valley. On the west, 
however, it is chiefly margined by Cretaceous beds, which in one or two 
places give way to unimportant outcrops of the Jura, and in the region of 
Hentz’s Peak to considerable outbursts of trachyte. Out of the rolling 
Cretaceous plains which lie west of the valley of the Platte, in the region 
of Fort Steele, is lifted a dome-like exposure of older rocks, consisting of 
the whole stratified series, from the middle Cretaceous down to the Silurian, 


ARCHASAN EXPOSURES. Pil 


with a long, narrow outcrop of Archean core in the centre. Although it is 
remote from either of the main ranges and quite detached from all other Ar- 
chzean masses, there seems little doubt that this exposure is really a part of 
the submerged continuation of Park Range, separated from the main mass in 
the same manner as Elk Mountain is separated from the body of Medicine 
Bow Range. The central ridge of Park Range varies from 11,000 to 
nearly 12,000 feet high, its loftiest peak reaching 11,976 feet. North of 
Mount Zirkel the summits are less elevated, and at the extreme north- 
western end the greatest altitude is reached in Grand Encampment Moun- 
tain, 11,063 feet. These three Archzean bodies—Colorado, Medicine Bow, 
and Park ranges—should be considered as a single chain, whose varied folds 
- and greatly diversified structure represent the top of a broad Archzean sys- 
tem; for the separating depressions—North Park, Platte Valley, and Lar- 
amie Plains—are really but the unimportant shallow basins in the Archeean 
topography in which the later material has been laid down, 

That the granitoid and erystalline-schist cores of these ranges are 
truly Archean in age, is indicated not alone by their characteristic pet- 
rological facies, but also by the fact that several actual contacts are 
exposed between the crystalline rocks and either the Potsdam sandstone or 
a series of conformably underlying slaty rocks presumably Cambrian. 
These exposed points of contact lie to the north and south of the area of 
Map IL, but have been visited and studied by the writer, to make sure of 
their relation. With regard to the Archzan core of Colorado Range 
within our limits, independently of the relics of superposed strata, it may 
be said in general to consist of a broad central anticlinal, having along its 
axial summit a very flat arch, the dip increasing rapidly as the rocks recede 
from the axis. Considered in longitudinal elevation, the former crest which 
must have marked the summit of this Archzean fold was neither a horizon- 
tal line nor a simple inclined one, but possessed several prominent sags 
or saddle-like depressions; so that the ideal axis of the range, viewed 
longitudinally, was a deeply undulating line. Furthermore, from longitu- 
dinal pressure it was also deflected in plan into considerable horizontal 
sinuosities, and consequently the sides of the anticlinal were alternately 


thrown into broad convex folds (upon which the strata were brought into 


22 SYSTEMATIC GEOLOGY. 


a state of strain), and recurved in broad reéntrant bays in which the beds 
were severely crumpled in secondary folds or confusedly dislocated. Added 
to these disturbances, was a third series of effects resulting from forces 
that tended to warp the anticlinal, which introduced an irregular shearing, 
and complicated not only the main fold but the secondaries. As a result, 
there is one broad central fold with numerous parallel subordinate axes, 
whose corrugations probably do not penetrate deeply into the strata. 

It is assumed that all this dynamic action took place after the crystal- 
lization and consolidation of the rocks themselves—in other words, after 
they had attained their present phase of metamorphism and crystallization. 
Subsequently to this system of compound folding, and still before the Cam- 
brian age, a wide-spread erosion teok place, rounding off and smoothing 
down the general forms; but it was absolutely powerless to produce sharp 
canons, or other abrupt features, and had the effect rather to reduce than to 
heighten the topographical effects of the folding and faulting. 

Before proceeding to localize any observations within this Archzean 
body, it will be well to give a condensed sketch of the sequence of the 
rocks involved in this range. It would be difficult to find a corresponding 
area in any Archaean country of greater petrological simplicity and unity. 
The chief rocks are granites and granitoid gneisses, with a few subordinate 
mica-schists, and in the uppermost or gneissic members a few limited sheets 
of hornblendic gneiss, the main series being composed of quartz, orthoclase, 
and mica (chiefly biotite), with a slight admixture of triclinic feldspar. 
The lowest exposures in the heart of the anticlinal consist of massive pearly 
and reddish-gray granites, composed almost entirely of quartz and ortho- 
clase, with a small but variable percentage of mica and a few minute crys- 
tals of triclinic feldspar, mostly oligoclase. These granites, exposed where 
erosion has deeply carved away the axial region of the range, or has cut 
profoundly into an especially disturbed portion of the flanks of the anti- 
clinal, are remarkably uniform in appearance, and are only varied in the 
amount of crumbling and decomposition which they show, in the propor- 
tion of mica, or in the ordinary variability in the size of the quartz and 
feldspar particles. The latter, either simple or twinned orthoclases, vary 
from an inch and a half to a size invisible to the naked eye. This granite, 


ARCHAAN EXPOSURES. 93 


which is a characteristic aplite, never presents a true bedding, but ap- 
proaches a tabular formation as the mica increases. Followed over consid- 
erable distances, its texture and color are found to change constantly, and 
in the more crumbling parts, where the granite “malady” has acted most 
deeply, are found large spheroidal masses of more enduring texture, which 
have resisted disintegration, and remain either single or in confused heaps. 
Directly succeeding this formation, and with no apparent unconformity, is 
a series of more noticeably red granites, showing a distinct bedding which 
defines their structural relations to the anticlinal. This latter series is com- 
posed, like the former, of quartz and orthoclase, in this case usually quite 
red, and mica rather more abundant than in the earlier group, which shows 
a constant tendency toward a gneissic arrangement of particles. There are 
no signs of the granite malady; on the contrary, the rock breaks with a 
sharp angular fracture and shows no effects of rapid disintegration. As in 
the earlier reddish pearl-colored variety, mica is often wanting, and indeed 
this member throughout its lower beds may be called a true aplitic granite. 
At its upper limits only does mica become a prominent mineral, and here 
it passes by a series of irregular but gentle gradations into true mica- 
gneisses. Owing to the innumerable faults and complicated folding upon 
the flanks of the range in the region chiefly occupied by the mica-gneisses, 
it is impossible, without very extended labor, to arrive at their thickness. 
There cannot be less than 12,000 or 18,000 feet of them, and there may be 
twice that amount. 

From the lowest exposures to the highest, there is a gradual passing 
from the structureless granitic form through simple broadly bedded gran- 
ites—which even in the field, without close examination, appear to possess 
no parallel structure, but upon close following are seen to shade through 
a general tabular bedding—up to a zone occasionally interrupted by true 
gneiss beds, which become more and more frequent until the bedded 
granites are entirely excluded from the series, and thereafter for a great 
thickness there appear only dark mica-gneisses; these, however, present 
a very great variety. South of the line of the Fortieth Parallel work, in 
the region of Ralston and Coal creeks, the late Mr. Archibald R. Marvine, 
of the United States Geological and Geographical Survey of the Territo- 


24 SYSTEMATIC GEOLOGY. 


ries, brought to light an overlying group of quartzitic, ferruginous schists 
and quartzites, whose probable equivalents will be described in a later part 
of this chapter, in localities farther to the west. Equally with the gneisses 
and mica-schists, the above-described granites are held to be of metamor- 
phic origin. 

Of truly eruptive rocks, there are unmistakably intrusive granites, 
powerful outbursts of gabbro, and dikes of felsitic porphyry, the latter 
enclosing within the microfelsitic groundmass a varying proportion of 
crystals of quartz, triclinic feldspar, and lepidolite. 

It was not within the scope or time of this exploration to cover ground 
with enough minuteness to map out boundaries of the various members of 
this series, and the above generalized sketch of the structure and sequence 
of rocks in our section of Colorado Range is only offered as a tentative 
explanation whose leading outlines may be relied on, but whose details will 
of necessity be found subject to slight modifications. 

The central or oldest body of granite is well exposed on the railroad 
from a little east of Buford Station westward to about two miles down the 
west slope from Sherman. It is here characterized in color by a pinkish 
orthoclase, and is noticeable for its extreme disintegration. To the north 
and south of the road, rising above the gravelly plateau country, are seen 
several bold outcropping groups of the hard spheroidal nuclei before men- 
tioned. Some of these forms reach 40 or 50 feet in diameter. Skull Rocks 
and Tower Rock are well known examples in the immediate vicinity of the 
railroad. The trend of this mass of granite is a little to the east of north, 
and so far as is now known it passes out upon the east side of the range. 
In other words, the axis of the modern range was slightly diagonal to the 
Archean fold. 

Passing southward from Sherman, the harder outcrops rise above the 
disintegrated material for a few miles, when there seems to be a gradual 
change in the character of the granite, which becomes harder, the feldspars 
larger and whiter, rather more mica makes its appearance, and the whole 
body seems to trend off to the southwest, probably parallel to the water- 
shed. In the broader part of the range, at the head of the South or Main 
Fork of the Cache la Poudre, the sharply folded rocks of Medicine Bow 


ARCHASAN EXPOSURES. 2a 


Range make contact with those of Colorado Range in a complex manner. 
The whole country, to the uppermost limits of the timber growth, is ob- 
secured by forests and glacial débris; but it seems quite clear that the older 
Colorado granite here passes under the Medicine Bow series and does not 
reappear at least as far south as Long’s Peak. If it reappears at all in 
that latitude, it must be to the west and below the red granites of Estes’ 
Park. The projecting mass in the northern part of the range, in the region 
of the Chugwater, which advances like a promontory into the eastern plains, 
seems to belong to the central and older mass of granite. 

If this slight chain of observations is correct, and it seems to be essen- 
tially so, the axis of the Archean fold is deflected westward from the merid- 
ian about 20°, from the northern limits of the map down nearly to Long’s 
Peak, where it turns into the line of the meridian and continues southward 
on that strike for many miles. The second series, or the bedded granites, 
as before mentioned, possess several distinctive features in contrast with the 
older family, and many features in common. Like the older rocks, they are 
distinctly aplitie for the most part, but at their upper limit, by the rapid 
accession of mica, they pass into distinct mica-gneiss. They are more 
compact, more massive, show more bedding, and in weathering result in 
less distinctly rounded forms. The granite malady does not seem to have 
affected them, and there are none of those regions of fine granite gravel, 
with harder nuclei outcropping. In general, they are of deeper colors, 
dark reddish grays and reds prevailing. On the railroad they are well shown 
_at Granite Canon, and may be traced thence north and south, the northward 
extension disappearing beneath overlying Carboniferous limestones at the 
head of the North Fork of Crow Creek. Southward along the range they 
reappear at intervals, the red granite of Estes’ Park and the lower Big 
Thompson offering well known examples. Besides biotite, these granites 
contain a second dark mica, which Zirkel identifies under the microscope 
as lepidomelane. A similar belt of granite bounds the west side of the 
older or central mass, appearing a few miles northwest of Sherman, and 
extending thence north along the west side of the range, disappearing in 
the region of the Sybille beneath westerly dipping beds of pearl-gray 


eneiss and black hornblendic schist. The same characteristics are observ- 


26 SYSTEMATIC GEOLOGY. 


able in this mass of flanking granite as in its companion formation upon the 
east of the range, as typified at Granite Canon. It is, perhaps, even more 
distinctly aplitic on the west than on the east. Passing southward, it 
crosses the railroad a few miles west of Sherman, and continues southwest- 
erly for an unknown distance. West of the head of Fish Creek and Sports- 
man’s Creek a similar red bedded granite is observed, which is probably 
the identical mass. About the head of the Main Fork of Cache la Poudre, 
overlying some obscure granite bodies, are found heavy masses of dark 
eneiss, which cannot be identified with any rocks lying to the north, but may 
be related either to the gneissic rocks of Medicine Bow Range, to be here- 
after mentioned, or to those dark mica-gneisses which are developed farther 
south on Colorado Range, in the region of Clear Creek. A peculiar dark 
red granite is seen on the railroad at Dale Creek bridge, which in some re- 
spects is a little different from any other in the range. It is of an intensely 
deep-red color, and contains broad, tabular crystals of red orthoclase; gray 
quartz, which seems to occupy a very subordinate position in crystallization, 
being chiefly wedged into the interstices between the orthoclase crystals. 
Like the Granite Canon rock, it contains lepidomelane. Under the micro- 
scope, Zirkel observed small triclinic feldspars. The bedded granite of 
Long’s Peak is remarkable in a general way for the predominance of twinned 
crystals of orthoclase, very much elongated in the direction of the bedding. 
These strata have a dip of from 5° to 8° to the east. The directly under- 
lying formation is of a distinctly bedded, coarse-grained, pinkish granite, 
much like that of Granite Canon, and is probably of the same horizon. 
The gentle slope of these easterly dipping beds carries the formation down 
along the waters of the Saint Vrain’s and Big Thompson nearly into con- 
tact with the overlying Trias. Near the modern rocks a gray granite, 
apparently the same as at Long’s Peak, reappears. Southward over the 
Long’s Peak rock are piled up the enormous series of gneisses, best shown 
on Clear Creek. Exposures on the upper Sybille, and those seen along 
the eastern base of the mountains in the region of Signal Peak, seem to 
be the representatives of the lowest members of this vast granitic series, 
the greater breadth and altitude of the range to the south retaining all the 


members of the fold, while to the north, owing to the gradual depression of 


ARCHAZAN EXPOSURES. 2 


the range and the constant encroachment of overlapping sedimentary rocks 
upon both sides, only the lower or core members are exposed. 

Aside from the above-mentioned rocks which constitute the members 
of this great fold, there is a most interesting feature in the occurrence of 
an immense mass of ilmenite, near the east base of the range, just north 
of Chugwater Creek, about a mile and a half abeve where it flows out 
upon the plains. It has an irregular oval plan, with a sharp definition from 
the enclosing granite, and rises in a bold boss about 600 feet above the bed 
of the stream. Masses of granite invade the ilmenite for a short distance, 
and in their turn protuberances of iron are nearly enveloped in surround- 
ing granite. The main mass is perhaps a quarter of a mile long, having a 
trend a little west of north, terminating quite abruptly to the north, but 
extending eastward, and followed by a train of irregular subordinate out- 
crops for about two miles toward Pebble Creek. In the vicinity of Horse 
Creek are smaller deposits, described by Mr. Hague in Volume II. Some 
normal magnetite and small amounts of hematite accompany the main body 
of ilmenite. In all these exposures titanic acid enters as a varying but 
usually very important component, ranging from 20 to 50 per cent. 

Graphite in impure thin beds, mixed with a bronzy decomposed iron 
pyrites, is found in the later granitoid rocks of the west side of Laramie 
Hills, and elsewhere through Colorado Range, in small, scattered occur- 
rences. 

In eruptive rocks our section of the Archean range under consideration 
is decidedly poor. The most important is the group of gabbros, found to 
the east of Iron (ilmenite) Mountain, and on Chugwater and Horse creeks, 
all within a narrow geographical area, where they come to the surface 
through granites and form low rough domes. It is essentially a bluish-gray 
labradorite, with a little finely disseminated hypersthene. A yellowish- 
white mica and some fine rounded grains of magnetite and ilmenite are 
also included with the mass. 

This association of graphite, ilmenite, and gabbro in the granitoid 
rocks of Laramie Hills, first observed in the West by Arnold Hague, will 
be commented on later in this chapter, 

Besides these there are distinetly intrusive granites and felsitie por- 


28 SYSTEMATIC GEOLOGY. 


phyries which occur along the southern line of our work and still farther 
south in the range. 

The porphyries are a microfelsitic groundmass composed of orthoclase 
(as shown by analysis), quartz, and a little triclinic feldspar. In this are 
enclosed rounded grains and rudely dihexahedral crystals of quartz, both 
covered with an opaque coating of fine feldspathic material, crystals of feld- 
spar (orthoclase as far as determined), and more rarely a white mica, doubt- 
less muscovite. 

Porphyry dikes appear usually not far from the middle or axial part 
of the range, and are found to trend either a little west of north or at right 
angles to that strike. 

The intrusive granites are for the most part combinations of quartz, 
orthoclase in slender tables and twinned crystals, and, curiously enough, 
muscovite instead of biotite. Triclinic feldspars, though uncommon, are 
occasionally present. 

Mepicine Bow Ranecr.—Viewed as a whole, the Medicine Bow offers 
more complexity, both of material and structure, than Colorado Range 
Although impossible to an exploration like this, a minute study of the super- 
position and flexures of its crystalline beds would furnish most interesting 
special results. While the data gathered by Mr. Hague seem to point with 
satisfactory agreement to a general theory of the range, on the other hand 
its exact relation to the contiguous body of the Colorado is not discovered, 
nor is it by any means certain that the whole series involved in the Medi- 
cine Bow is conformable throughout. 

The materials of the range are composed of gneisses; hornblendic, 
often dioritic, schists; variable schists made of quartz, mica, and both sys- 
tems of feldspar, in changing proportions; quartzitic schists; argillites; 
massively bedded quartzites and limestones which pass into quartzite by the 
giving out of calcareous matter; and lastly subordinate granites and erup- 
tive diorites. 

All the observed positions south of a line joining the mouth of French 
Creek and Sheep Mountain, with obviously local or superficial exceptions, 
indicate a northwest strike and southwest dip. North of this line two dis- 


tinct axes, approximately parallel and trending about north 20° to 25° 


ARCHAAN EXPOSURES. 29 


east, are developed across the range; an anticlinal lying a little west of 
Medicine Peak, and the companion synclinal occupying a depression 
between Medicine and Mill peaks. Rocks having a northwesterly dip rise 
from the Platte valley up to the heights on Upper Brush Creek, pass over 
the anticlinal, and dip down and east through Medicine Peak, rising again 
with a westerly dip at Mill Peak ridge. These two transverse axes 
embrace within their folds the iridescent schists, quartzitic schists, argillites, 
quartzites, and limestones. Their relation to the older and underlying mica 
gneisses and various hornblendic schists and dioritic gneisses is apparently 
that of conformity—at least no nonconformity has been observed; for- 
ests, débris, and local folds conspiring to mask a relation obscure enough 
under favorable exposures. Whether conformable or not, there are here 
two series of rocks. The lowest, which have an enormous development, are 
the gneisses and hornblendic beds, all characterized by the important pres- 
ence and the frequent predominance of plagioclase over orthoclase, by the 
general (though not unexceptional) absence of red color among the feld- 
spars, the occurrence of silvery white micas in some gneisses, and frequency 
of beds with the composition of diorite. Above these the schists, quartzites, 
conglomerates, and limestones of Medicine Peak group form the second 
series. Neither of these seems to correspond, either mineralogically or in 
broader characteristics, with any portion of Colorado Range within our 
field. There is, indeed, an apparent resemblance between the Medicine 
Peak series and that described by Archibald R. Marvine* at Ralston Creek, 
but it disappears on close comparison The probable mutual relations of 
these members of the Archzan is reserved for a later section of this 
chapter. 

In the region where this elevated mountain block comes in contact 
with Colorado Range proper, particularly where a high ridge is developed, 
culminating in Clark’s Peak and Mount Richthofen, the geological relations 
of the two ranges are difficult to make out. Forests and glacial dcbris 
combine to offer serious difficulties to a more lengthened study than our 
exploration permitted. 

Topographically, the most noticeable feature is the defined line of ridge 


* United States Geological and Geographical Survey of Colorado (1873), p. 189. 


30 SYSTEMATIC GEOLOGY. 


and peaks which forms the extreme western boundary of the high mountain 
area, sharply descending beneath volcanic bodies and upturned stratified 
formations along the east boundary of North Park. The singular trough- 
like depression which separates this southernmost group of Medicine Bow 
Range from the chain of central elevations of the Colorado body is occupied 
by Cache la Poudre and Laramie rivers, which together define a line of 
depression parallel with the Clark’s Peak ridge. ast of this lies the anti- 
clinal of Colorado Range already described. The Clark’s Peak wave, as 
far as can be seen, consists of another and probably a later series of rocks. 
Structurally, these two series bear a relation to each other not unravelled 
by actual observation, but inferred, from their relative position, to be a 
nonconformity. 

Along the eastern edge of North Park sedimentary border, with a 
universally obvious unconformable underlie, is seen a series composed for 
the most part of steeply dipping gneisses and gneissoid beds, which consti- 
tute the main west slope of the Clark’s Peak ridge. Unlike the series of the 
Colorado, they contain, besides quartz, orthoclase, and biotite gneisses, a 
predominance of sheets in which hornblende and plagioclase are prominent 
if not the chief ingredients. Near the base of the ridge, a few miles north 
of Clark’s Peak, are conspicuous beds made up of pale pinkish feldspar and 
bright green hornblende. Besides the predominating orthoclase, distinct 
small crystals of colorless plagioclase are present. With the exception of 
this limited belt, the feldspars, of whichever system, contained in these 
eneisses are usually colorless. A typical gneiss of the region occurs directly 
west of Clark’s Peak, consisting of biotite, hornblende, quartz, orthoclase, 
and plagioclase, the latter two nearly white, and a little microscopic apatite. 
Near the base of the peak occurs a granite not far removed in composition 
from the orthoclase and quartz aplite of Laramie Hills. 

Clark’s Peak itself and the ridge in its neighborhood, as well as a broad 
area to the north, offer a variety of granites. That of Clark’s Peak is quite 
devoid of any gneissic parallelism of minerals, and is of such uniformity 
and massive habit as indicate an eruptive origin. It is composed of limpid 
white quartz, orthoclase, plagioclase, biotite, and apatite. The mineralogi- 


cal equivalency between this rock and the gneiss lying to the west and down 


ARCHASAN EXPOSURES. oil 


the slope will be noticed, and will naturally suggest that the summit rock 
is only a structureless equivalent of the gneiss, representing a further con- 
dition of metamorphism. Hornblende in the gneiss, however, offers a per- 
manent difference. 

On the summit northwest of Clark’s Peak is observed a dark gray 
granite, composed of colorless quartz; feldspar, both orthoclase and plagio- 
clase; and a dark mica present in large proportion, and arranged in paral- 
lel layers. 

Three or four miles south of the peak, ina coarse-grained granite which 
occurs near the foot-hills, carrying large crystals of vitreous oligoclase, Zir- 
kel detected the presence of zircon in red grains very like those occurring in 
the zircon syenite of Norway. It is in this southern portion of the range 
only that true granites are observed. 

North of this region the defined ridge breaks down into a broad roll- 
ing plateau heavily covered with forest and soil, over which little of the 
orographic structure can be learned. Observations along the Laramie, as 
well as on the edges of the park, indicate a region of varied gneisses, in which 
dioritic beds are prominent. While several confused folds seem probable, a 
prevailing dip to the southwest is seen. From the heights above the north- 
east edge of North Park a specimen was obtained representing a not unfre- 
quent type, composed of almost blackish-green hornblende, bluish-white, 
brilliant plagioclase, in slender prisms, often a quarter of an inch long, and 
a little limpid quartz and biotite, the latter in very subordinate quantity. 
The northwest strike of these westerly dipping gneisses is often varied by 
sharp zigzags. Along the northeast region of the park, especially in the 
foot-hills, gneisses and schists, dipping rather steeply to the west, have their 
strike arranged en échelon, with the long member trained in a northwest direc- 
tion, and short, abrupt cross-strikes more nearly in an east-and-west course. 

Exposures on the east side of the Platte Canon indicate a gencral east- 
erly dip, at least toward the lower reaches of the river. 

Between the upper cation and Laramie River but little geology could 
be obtained; rounded, forest-covered knolls and ridges, showing but few 
outcrops, alternate with peculiar treeless, grassy glades, which seem to open 


pathways through the timber quite independently of drainage-lines. Along 


Bye SYSTEMATIC GEOLOGY. 


the Laramie valley, however, and northward, near the eastern limit of the 
Archean body, as far as Sheep Mountain, dips were observed which indi- 
cate a general westerly slope for the gneisses. 

Where the North Platte leaves its Archaean canon to debouch upon 
the broad Tertiary valley, two prominent hills rise upon the left bank: 
Bennett’s Peak, opposite the confluence of Brush Creek with the Platte, 
and River Butte, five miles below; the former about 600, the latter 900 feet 
above the river plain. Both are made up of steep, westerly dipping beds 
of dioritic gneiss. 

Upon the hills east of the river, between French and Brush creeks, are 
sandy mica gneisses striking north 45° to 55° west, with a southwesterly 
dip, having a parallel arrangement of minerals and a banded appearance. 
Hornblende does not enter into the composition; transparent, colorless 
quartz, mica, orthoclase, and plagioclase complete the list of constituents, 
and make an association rather unusual in this region; plagioclase, when 
present in important percentage, usually implying a considerable amount of 
hornblende. In the oldest granite of the Laramie Hills there is indeed a 
little plagioclase without hornblende, but it is often discoverable by the 
microscope only, and never plays a réle of importance. 

Intercalated in the last-named group is a narrow sheet of dark, dioritic 
material, probably of a common origin with the other crystalline schists, 
but presenting some of the characteristics of an intrusion. It is a combi- 
nation of hornblende, plagioclase, and a very little colorless orthoclase. It 
presents some interest under the microscope, for which the reader is referred 
to Professor Zirkel’s Volume VI. of this series. 

North from Brush Creek, mica gneisses with included sheets of horn- 
blendic schist, usually of dioritic composition, and occasional beds of vitreous 
quartzite, continue for about fifteen miles. They show many discordant 
dips, but incline prevailingly to the north. This radical change of position 
from the rocks farther south and east is due to the development of a strong 
anticlinal, trending along the range in a northwest direction, roughly per- 
pendicular to the northeast axis of the Laramie Hills. 

Gneiss beds, similar to those described on Brush Creek, occur on the 
crest of Deer Mountain near the head of Cedar Creek. They are rather 


ARCHAAN EXPOSURES. 33 


poor in mica, but are characterized by unusually white clear feldspars and 
small red garnets. Farther down on the peak are hornblende-piagioclase 
schists with a variable percentage of orthoclase, showing also under the 
microscope chlorite, titanite, zircon, and apatite. 

Hornblende gneisses, which vary greatly in the proportion of quartz, 
and have a general strike north 40° west, with a southwesterly dip, are 
observed north of Deer Mountain, making a local exception of the northerly 
dip observed in this section of the range. A change takes place north of 
Cedar Mountain, light mica gneisses taking the place of the hornblendic 
variety which has prevailed along the western margin of the range. 

An interesting gneiss occurs at Cherokee Butte, an eminence on the 
narrow Archean isthmus connecting Elk Mountain with the main range. 
It is hard rock, composed of gray quartz, white and flesh-colored feldspar, 
both orthoclase and plagioclase, and a little scattered, thin, flaky mica. Zir- 
kel calls attention to the condition of the quartz, which is made up of small 
worn and rounded fragments. Directly west of this body is a gray gneiss 
carrying a little hornblende and microscopic titanite. 

Nearly half of Elk Mountain, whose detached mass forms the north- 
ern extremity of the range, is of Palaeozoic and Mesozoic rocks. Archean 
gneissic beds form the summit and southern portions, however, and unite it 
with the isthmus of Cherokee Butte. These beds strike from north 45° to 
north 70° east, and dip to the north and west at high angles, often approach- 
ing the vertical. Quartz and monoclinic and triclinic feldspars, intimately 
mingled, are the main constituents, but the gneissic structure is given by a 
chloritic mineral arranged in fine-grained bands. Where the materials are 
all very fine, as at the base of the series, the rock wears the aspect of an 
impure quartzite. 

Thus far the southern portion of the range and the south and west 
flanks of its main mass have been briefly described. With the exception of 
the granites of the Clark’s Peak region, these formations have been seen to 
consist of a varied body of gneisses, in all of which, with slight exceptions, 


both systems of feldspar and quartz have been present, with either horn- 


blende or mica—rarely with both. 
Dioritie gneisses, closely approaching the minuter characteristics of the 


0K 


34 SYSTEMATIC GEOLOGY. 


eruptive diorites, are intercalated conformably in the general series, while 
in exceptional localities there are masses of a rock of dioritic nature, which 
are probably true dikes. 

At Medicine Peak, which reaches 12,231 feet in altitude and is the cul- 
minating mountain of the range, appears a new geological feature. The 
peak itself, and the ridge from which it rises, are formed of a heavy body of 
remarkably white quartzites, approximately 2,000 feet in thickness, strik- 
ing north 20° to 25° east, and dipping east at a high angle. The zone is 
irregularly stained a pale reddish hue by thin seams of oxydized iron min- 
erals. Toward the bottom of the series is a zone of pale bluish quartzite, 
rather more coarsely grained than the overlying members, and intercalated 
with sheets of conglomerate holding smooth quartz pebbles in a fine siliceous 
paste. Cyanite in narrow veins, associated with colorless quartz, is charac- 
teristic of the quartzite belt. A more prominent and conspicuous feature is 
the series of diorite dikes cutting the quartzites at nearly right angles with 
the strike of the strata. The material of these unmistakably eruptive dio- 
rites is nearly identical with the dioritic schists. 

South of Medicine Peak, on the head waters of French Creek, con- 
formably underlying the quartzite series, is a body of argillaceous slates, 
which have a fine lamination but rather imperfectly developed cleavage in 
the direction of the strata-planes. A great deal of excessively fine mica is 
visible under the loupe. A thickness of about 400 feet is assigned to this 
group of rocks, from the plane of contact with the quartzites down ; whence, 
becoming rather impure and more quartzitic, they pass abruptly into a series 
of harder quartzitic argillites enclosing beds of ferruginous, siliceous schists 
These in turn are underlaid by a more highly crystalline zone of schist, in 
which the original lamination appears to be for the most part obliterated. 
Exposed faces are seen to be dotted over with concretionary bunches or 
knots of fibrous hornblende, much of which is decomposed and coated with 
a bronze-green, red, and purple material of a peculiar and often brilliant 
iridescence. 

Farther down French Creek are silver-white, muscovite, mica slates 
and quartzose slates, dipping 70° to 75° east and striking north 15° east. 


Over them appear heavy masses of quartzite, which are doubtless the south- 


ARCHAAN EXPOSURES. Do 


ward continuation of the Medicine Peak beds. Still lower in the canon 
appear the same heavy beds of light mica gneiss characteristic of the south 
flanks of the range, coming in under the schist zone with apparent con- 
formity. 

About ten miles east of Medicine Peak, and separated from it by a 
rolling timbered upland country, is a strong north-and-south ridge cul- 
minating in Mill Peak, which reaches an altitude of 10,596 feet. Here a 
series of quartzites, conglomerates, and schists, doubtless equivalent to 
Medicine Peak ridge, reappear, but with a reversed position, dipping west 
and defining the east side of a broad synclinal. The quartzites are more 
stained and infiltrated with iron oxyd than at Medicine Peak; the conglom- 
erates also are more important and are somewhat different, being a red, 
and including large angular cherts and ferruginous quartzite pebbles. 
The actual summit of Mill Peak is of a light gray and white siliceous lime- 
stone, resembling a quartzite; indeed, the two rocks, by a varying of 
siliceous and lime particles deposited together, are made to shade through 
the intermediate gradations and illustrate a complete but gradual change 
of sediment. 

Along the northern foot-hills of the range, and for considerable dis- 
tances up Cooper and Rock creeks, are exposed dark schists and mica 
gneisses, the direct equivalents of those along the southern foot-hills. 
South of Little Laramie River, about Bellevue Peak, similar hornblendic 
and micaceous crystalline rocks are found, and among other forms white 
mica gneisses. Amongst them is one noticeable white or silver-gray gneiss, 
whose constituents are colorless, clear quartz; pearl-colored feldspar, in 
general very lustrous, but sometimes altered; a little brown mica, both 
generally disseminated and segregated in bunches and nodules; and minute 
grains of red garnet. On the northern and eastern slopes of this region 
occur banded and irregularly bedded rocks, made up of variable per- 
centages of hornblende and feldspar. 

Between the above-mentioned leading formations and those noted in 
the description of Colorado Range, a few common characteristics will have 
been observed, but noticeable differences prevail. The two ranges are sin- 


gularly unlike. In the essential construction of the rocks are observed 


36 SYSTEMATIC GROLOGY. 


quartz, orthoclase, plagioclase, hornblende, mica, chlorite, and calcite. This 
difference is observable also in the general list of accessory products. 
Small quartz veins traversing the gneisses and hornblendic schists are often 
observed, particularly in the neighborhood of Brush and Cottonwood 
creeks, on the western foot-hills. They carry gold in small quantities, 
magnetite, pyrite, and massive epidote and cyanite. Red and reddish- 
brown grains of garnet are found, always associated with the light-colored 
gneisses, as at French Creek and Deer Mountain. Zireon, apatite, and 
titanite were detected by Zirkel under the microscope. 

Park Raner.—As an independent body, Park Range has its northern 
termination within the area of this work. Its eastern flank is sharply bounded 
by North Park and the North Platte valley; on the west it connects with 
the elevation of the Elk Head group and an irregular, hilly country about 
the upper Yampa River. As a range, it ceases a few miles northwest of 
Grand Encampment Peak. From our southern boundary, as far north as 
Pelham Peak, it is a distinct meridional ridge, with a sharp slope to North 
Park, and a broad summit, which was originally a plateau made up of strata 
gently dipping to the west, but now a mere net-work of plateau ridges, sep- 
arated from one another by deep glacial canons. Near Pelham Peak the 
range is abruptly bent round into a northwest trend, which it preserves for 
about thirty miles, and then plunges down under the Tertiary strata of the 
lowlands. The Archean body which forms the most important geological 
feature of the range is bounded on the east by the Tertiaries of North Park 
and the Platte valley, with the narrow exceptions of a body of basalt out- 
poured in the region of Rabbit Ears Peak, short stretches of Cretaceous 
east of Ethel Peak and at the northern entrance to the Park, and a strip of 
Triassic sandstone exposed against the granitic tongue east of Arapahoe 
Creek. On the west the upturned Jurassic and Cretaceous rest along the 
base of the range and border the Archzean series. In the region of Hentz 
Peak, voleanic outbursts also edge the Archean mass. The crystalline body 
itself is a single anticlinal fold, of which that portion of the range south of 
Pelham Peak is the westerly dipping half. The easterly dipping half shows 
only in the extreme eastern foot-hills and in the projecting spur which lies 
between Big Creek and North Park. The main body, therefore, is the half 


ARCHASAN BXPOSURES. 37 


of an anticlinal, the other half having suffered a deep downthrow, which has 
left only traces of the easterly dip. 

The western-dipping beds present their eroded edges along the steep 
eastern front of the range, and are seen to incline very gently, gradually 
rounding to a steep inclination along the western foot-hills. North of Pel- 
ham Peak the fold has been flexed round into a northwest strike, giving the 
topographical trend as well as the direction of strike. In this northern por- 
tion the complete anticlinal is present. In the angle of flexure between the 
north and northwest trending parts there is much local crumpling and the 
development of a secondary lateral axis which opens an inclined synclinal 
from the summit of the range near Pelham Peak in a southwest direction. 
The meridional part of the main axis indicates a horizontal profile for the 
original fold, but north of Grand Encampment Peak the axis dips to the 
northwest, and, aside from the bevelling off by erosion, actually inclines 
downward and under the overlying 'Tertiaries. 

The series of Archzean rocks involved in this fold are bedded granitic 
gneisses of uniform constitution and material, but widely varied arrangement 
of internal structure, hornblendic schists, and dioritoid rocks, besides limited 
quartzites. Of Archzean eruptive rocks there are none, unless some obscure 
dioritic bodies are intrusive, 


and all the evidence points the other way. 

A granite occurring in the southern part of the range finds a characteristic 
expression on the summit of Ethel Peak. It is a rather coarse-grained mix- 
ture of grayish quartz, red orthoclase, sparsely but rather evenly dissem- 
inated biotite, and rare triclinic feldspars, the biotite often adhering strongly 
to the orthoclase faces. While the: rock as a whole shows a broad, distinct 
bedding, there is no parallelism in the arrangement of individual minerals. 
On exposure, it crumbles rather readily and breaks with a rough, irregular 
fracture. It distinctly resembles some of the bedded reddish granites of 
Colorado Range. 

Crawley Butte and the long, tongue-like ridge which juts southward 
from the range bounding the east side of Arapahoe Creek valley, the two 
being geologically one body, are for the most part composed of a similar 
red orthoclastic granite. Another tongue-like projecting ridge advances 


in a southeast direction from Park Range, forming the northwest boundary 


38 SYSTEMATIC GEOLOGY. 


of North Park for a few miles. Here a variety of granites occur; among 
others, a coarse pegmatite consisting of pellucid or milky-white quartz, large 
groups of confused, imperfectly crystallized, red orthoclase, masses of bio- 
tite, and muscovite, the latter mica predominating and occurring in much 
larger sheets. Great variation is observed in the quantitative proportion 
and arrangement of the minerals. There are segregations of considerable size, 
altogether made up of one or the other mineral. One variety is essentially 
a feldspar rock, with the few grains and crystals of quartz or mica present 
only as segregated groups, while disseminated through the red orthoclase are 
irregular veinlets and waving lines of yellowish-green epidote, making a rock 
equivalent to that described by Frank H. Bradley* from Unaka Range, 
Blue Ridge chain, between North Carolina and Tennessee. 

Between Bruin Peak and the Tertiary valley the granites assume a more 
regular type, composed essentially of quartz and orthoclase, with beds in which 
either mica or hornblende is present, rarely both. Gneisses are exposed in the 
same neighborhood. These also are variable as regards the presence and pre- 
dominance of mica and hornblende, but the latter perhaps exceeds the former 
in importance. One special rock was found here, composed for the most 
part of brilliant black or dark-greenish hornblende, although carrying more 
or less white plagioclase and a very little quartz. It is distinctly bedded, 
and dips at a high angle a little to the north of east. Hornblende also ap- 
pears in considerable prominence in the orthoclase-mica gneisses. A final 
variety of gneiss is almost a mica schist, in which feldspar and quartz are 
minor constituents, the micas, both biotite and muscovite, arranging their 
flakes in strictly parallel planes. Zirkel finds especial interest in the micro- 
scopic examination of this species, as the reader will see by reference to 
Volume VI. 

Upon the walls of the glacial catons around Mount Zirkel, as also upon 
the peak itself, there is a similar association of mica gneisses and hornblendic 
schists. A distinct bedding may be traced along the canon flanks, gently 
dipping to the west. By the predominance of one or the other mineral, a 
black, white, or gray color is given to the individual sheet. Hornblende, 
combined with orthoclase, plagioclase, and very subordinate quartz, con- 


*American Journal of Science and Arts, May, 1874; page 519. 


ARCHASAN EXPOSURES. 39 


stitutes the leading type of bed, and the hornblende prisms commonly 
lie with the bedding-planes. Mica gneisses are present, however, carry- 
ing always a little hornblende and triclinic feldspar. Feldspar bands, 
faintly striped with hornblende, zones of pure feldspar, segregations of 
amphibolite, and sheets of hornblende striped with a little triclinic feldspar 
and quartz, alternate in every variety of arrangement. 

The trail up Grand Encampment Creek passes many excellent expo- 
sures of the Archean series. Near the mouth of the canon is a granitoid 
gneiss of orthoclase and quartz, with very imperfectly developed bedding. 
Biotite, instead of the ordinary parallel or banded arrangement, is grouped 
in large lenticular aggregations, whose longer axes are parallel with the gen- 
eral structure of the rock. Passing into a crude, coarse granitic form, this 
same rock distinguishes itself by the development of other segregations of 
quartz or feldspar not unlike those of Mount Zirkel. Overlying this series 
is a dark, hornblendice rock, in which white plagioclase crystals are scat- 
tered at irregular angles, as in a porphyry. 

Farther up the creek is a granite nearly related to the red orthoclase 
granite of Colorado Range and those about Ethel Peak of the range now 
under consideration. In this coarse and variable granite are frequently seen 
what are usually reserved for the microscope to reveal, namely, fissures in 
the feldspars filled with quartz, in which are embedded other feldspars as 
well as quite perfectly developed micas. Flesh-colored orthoclases in these 
coarse granites often attain a size of four or five inches. The other ex- 
treme of texture is also sometimes shown in this rock, when it passes into 
an excessively fine-grained aplitic form, with little or no mica. When 
present, the mica is apt to show an obscure parallelism. Zirkel demon- 
strates that the red color of these feldspars is due to oxyd of iron infiltra- 
tions in the minute fissures of the crystals, and also that the mica is 
accompanied and sometimes replaced by a strongly dichroitic chloritic 
mineral. As in the kindred granite of the Colorado, the quartzes are poor 
in fluid inclusions. 

On the slopes of the high peak southeast from Encampment Meadow 
is a series of hornblendic rocks and gneisses presenting the same yaried 


petrographical habit as at Mount Zirkel. In one of the mica-bearing zones 


40 SYSTEMATIC GEOLOGY. 


of true gneiss are observed red garnets; and so close is the resemblance be- 
tween the garnetiferous gneisses in all three of these Rocky Mountain ranges 
as to suggest that they may not improbably represent a common horizon, On 
the peak are alternating beds in which first plagioclase and then hornblende 
predominates, with quartz containing in some instances liquid carbonic acid. 
Upon the summit of Grand Encampment Peak is also a dark-green amphib- 
olite, quite free from other minerals, but carrying an interstratified bed of 
an association of rocks to be hereafter noticed 


white, micaceous quartzite 
as recurring in Humboldt Range. 

Gneissic beds having the same variations as have been already 
described form the whole northwestern part of the range, dipping from the 
axis northeast and southwest. At the extreme north end of the range, where 
the northerly dipping Archzean beds plunge down under horizontal Tertia- 
ries near the mouth of Jack’s Creek Canon, interbedded in a dark, horn- 
blendic schist, is a bed of pure, dazzlingly white quartz, 50 feet thick, of 
singular purity, vitreous and only varied by wandering vein-like clouds, 
which under a high magnifying power were resolved by Zirkel into regions 
immensely rich in fluid inclusions, partly of water and partly of liquid car- 
bonic acid. There is also a hornblende, orthoclase-plagioclase rock, with 
but little quartz; orthoclase, the predominating feldspar, giving it the gen- 
eral composition of a syenite, which it would undoubtedly be considered 
but for the certainty of its belonging to the strictly metamorphic series. 
While planes of bedding and even the ordinary gneissic parallelism of 
minerals are sometimes wanting, there are seen such infinite variations in 
the internal arrangement of the crystalline series in these ranges that only 
the most positive evidence of intrusive origin should be accepted. This 
syenitic type, a most unusual one, is confidently referred to the gneisses, all 
of which are here metamorphic products. 

Not far from the syenitic body of Jack’s Creek are beds which are a 
crypto-crystalline mixture of dark-green hornblende, with white plagioclase, 
probably oligoclase, often in long, slender crystals. This again is a rock 
without appearance of stratification or parallel arrangement of minerals, to 
all intents a diorite, yet believed to be a member of the series of dioritic 


gneisses. Dense forests obscure the western flanks of the range; but 


ARCHAAN EXPOSURES. 4] 


enough is known to say that the prevailing rocks are hornblendic gneisses 
dipping rather steeply to the west and southwest. 

Under the voleanic rocks at the head of Snake River is a red gneissoid 
rock made up of quartz, orthoclase, plagioclase, and minute flakes of mica, 
without general bedding or the true schistose structure, yet possessing a 
banded arrangement of the quartz and mica. Quartz is especially abun- 
dant, the grains welded together almost in continuous sheets. The ortho- 
clase is red; plagioclase oceurs in thin, colorless, acicular prisms. The 
same rock reappears at Camel Peak at the bend of Snake River. At Buck 
Mountain, near the head of Elk River, is a dioritic rock similar to the one 
already described on Jack’s Creek, equally free from schistose or gneissic 
internal structure, equally like the eruptive rocks in habit, but still in all 
probability metamorphic. 

The list of essential constituent minerals in the Park Range rocks is 
even more limited than that of the Colorado or Medicine Bow. It com- 
prises quartz, orthoclase, plagioclase, biotite, muscovite, hornblende, and 
epidote. Accessory species are garnet, magnetite, and gold. Under the 
microscope Zirkel detected, besides these, chlorite and apatite. Epidote as 
an essential constituent was only seen in the red unakite of Bruin Peak; it 
appears in a subordinate role in several coarse granites. Garnet of a rasp- 
berry color occurs in several highly micaceous gneisses, always in rocks with 
a close family resemblance to mica schist. The garnet grains are commonly 
as small as a mustard-seed, but occasionally longer, as in the gneiss of the 
high peak southeast of Encampment Meadow. In the hornblende gneisses 
of the same peak are numerous microscopic apatites, associated with twinned 
orthoclase in elongated forms like those on Long’s Peak. Unmistakably 
eruptive granites, or indeed other forms of intrusive rocks, do not exist in 
our part of Park Range. 

An Archean exposure northwest of Rawlings Station is without doubt 
an outlying dependence of Park Range. As before seen, the gneisses and 
granites of that ridge dip northwest and downward under the later sedi- 
mentary formations. Twelve or fourteen miles farther in the same direc- 
tion, there is a local elevating disturbance at Savory Plateau, where a 


doming up of the Cretaceous takes place, with quaquaversal dip and an 


42 SYSTEMATIC GEOLOGY. 


exposure of the underlying Jurassic series. No one can doubt the propriety 
of regarding this occurrence as an effect of the submerged continuation of 
Park Range. 

A similar but more important doming takes place at the locality north of 
Rawlings Butte, involving all the strata from the middle Cretaceous down to 
the Archean. The truncation of this dome by erosion has laid bare the entire 
series. Underlying the primordial sandstone is a long, narrow, nucleal mass 
of a granitoid gneiss, with comparatively distinct bedding, a northerly strike, 
and a dip of 45° to the west. A northwest valley has been eroded through 
the dome, doubtless on the line of some important fissure, leaving the 
best Archaan exposures on the east side of the valley. An interesting 
exhibition of the grinding power of wind-driven sands is here met with, 
the more exposed granite surfaces bearing a remarkable polish and grooving. 
The rock is a close-grained, strongly cohering mixture of quartz, plagio- 
clase, a little orthoclase, and hornblende, the latter disseminated in light- 
green fibres through the mass and imparting to it a prevailing greenish color. 
Strictly speaking, the rock possesses the composition of a quartziferous 
diorite with a distinctly granitic habitus, and may be regarded as highly 
quartzose dioritic gneiss. Zirkel points out that the quartzes are rich in 
fluid inclusions, some of which contain salt cubes and others liquid ear- 
bonie acid. 

Uinta Raner.—From the last-described exposures, westward across 
the whole basin of Green River, as far as Wahsatch Range, within the 
limits of the Fortieth Parallel Exploration, the entire area is made up of 
rocks later than Carboniferous, and there is but one outcrop of Archean 
age. This is a small body near the northern foot-hills of the eastern end 
of Uinta Range, and directly north of Green River, at the eastern end 
of Brown’s Park. The exposure is from four to six miles across from north 
to south, and about seventeen miles east and west. On the south it is 
bounded by the great sandstone series of the Uinta, except where between 
Red and Willow creeks the Tertiary of Brown’s Park abuts against it. Along 
the north it is chiefly bounded by Cretaceous rocks, which are probably 
brought into contact with it by a fault and a downthrow. A distinct non- 


conformity between the Archzean body and the Uinta sandstone is observed 


ARCHAAN EXPOSURES. 43 


on the line of contact west from Garnet Canon, and with equal distinctness 
and more satisfactory exposure north and west from the mouth of Willow 
Creek Canon. This long, narrow body, having an east-and-west trend, is 
the only Archean mass for more than 100 miles east or west, and for certainly 
an equal distance to the north, while to the south none is yet reported 
within a similar area. Garnet Canon, cut by Red Creek directly through 
the mass, and giving exposures of over 2,000 feet on either wall, offers the 
best view of its interior structure. The general plan is that of a flexed anti- 
clinal, or perhaps a double anticlinal, with converging axes, the fold of the 
northwestern portion being northwest-and-southeast, and that of the south- 
ern, northeast-and-southwest. The beds are very sharply uplifted, standing 
at angles of from 45° to 70°, and showing within the series much abrupt 
and severe plication. 

The group consists of pure white quartzites, hornblendic schists, and 
hydro-mica (paragonite) schists, richly charged with garnet, staurolite, and 
minute crystals of cyanite. The black, hornblendic beds are essentially an 
amphibole rock, containing a little quartz and sparing triclinic and ortho- 
clastic feldspars, the former predominating. Composed as it is almost en- 
tirely of distinct hornblende prisms, it might be fairly classed as an amphibole 
rock, and it is clearly to be correlated with that already described at Bruin 
Peak on Park Range. The association of paragonite with staurolite, garnet, 
and cyanite recalls many well known Appalachian localities and the classic 
St. Gothard of the Alps. The association of quartzite with hornblendic 
beds and cyaniferous schists suggests a resemblance to the series exposed on 
Medicine Bow Peak, which also carry cyanite; but the staurolitic-parago- 
nite rocks are entirely wanting in every other locality examined by this 
survey. In a measure this exposure stands as disconnected petrologically 
as it does geographically. It is the single instance in the Fortieth Parallel 
Archean area, aside from chloritic ingredients of certain granitoid rocks, 
of a hydrous rock; serpentines, steatites, damourite rock, and other hy- 
drated silicates being altogether absent. 

Minutely studied, the great white quartzite belt, with its intercalated 
beds of dark amphibolitie schists, yields the important fact, that while each 


individual stratum is most persistent in retaining its mineral and chemical 


44. SYSTEMATIC GEOLOGY. 


character when followed longitudinally, adjoining beds may and do differ 
widely. A clean bed of spotless white quartzite between two dense black 
sheets of amphibolite preserves its purity even when followed for miles. 
Whatever, therefore, may have been the cause or mode of metamorphism, the 
resulting mineral combination was governed absolutely by the chemistry of 
the original sediment ; nor did the process of change have power to transfer a 
single atom of a single clement out of the horizon in which it was deposited. 
Wausatcu Rangr.—The Archean rocks in the explored portion of the 
Wahsatch are exposed at intervals along the west front of the range for 
nearly 100 miles, and are composed of granites, garnet rocks, aplitic schists, 
and a very extended series of gneisses and hornblendic schists, with sub- 
ordinate quartzites. The manner of their exposure is of very great interest, 
involving the most extensive dynamic action observed within the limits of 
the Fortieth Parallel Exploration. The chain of outcrops clearly represents 
an old Archaean range of bold configuration, which has been buried beneath 
an enormous accumulation of Palzeozoic and Mesozoic sediments. It was 
this buried Archean range which controlled the position and direction of 
the modern Wahsatch Range. After the uplifts took place, and the Paleo- 
zoic and Mesozoic strata were thrown into their present inclined position, a 
great longitudinal fault occurred throughout this whole portion of the range, 
by which the entire western half of the ridge was thrown downward from 
3,000 to 40,000 feet, and is now entirely buried beneath the Pliocene and 
Quaternary formations of the Salt Lake basin. The present abrupt west 
front of the Wahsatch is the standing face of this great fault, and here the 
Archean rocks are seen to occupy the core of the range, unconformably 
underlying the Paleozoic series, and rising to different stratigraphical hori- 
zons in the overlying series. In the southern portion of Map IIL, in the 
region of Cottonwood and Little Cottonwood caiions, is exposed an approxi- 
mately conformable series of 30,000 feet of Paleozoic strata, overlying 
the granites and schists which there together form a portion of the early 
Archean surface. The origin and nature of the granites at this point are 
obscure. ‘There seem to be two distinet types—a granitoid gneiss, having 
a decided stratification, and an apparently eruptive body, which possesses in 


wi interesting degree the conoidal structure so prominently developed in the 


TAH 


ANGE 


) 
ye 


ARCHASAN EXPOSURES. 45 


granites of the Sierra Nevada. About fifteen miles south of Salt Lake City 
the Palaeozoic beds are thrown into a broad, semicircular curve, having a con- 
vexity to the east and a varying dip always away from the centre of this 
curvature. The ends of the strata of this great flexure advance westward 
until they approach the region of the great fault, their eroded edges forming 
the foot-hills of the range. 

The centre and nucleus of this immense curvature is a body of 
Archean rock, composed partly of schists, but principally of a great cen- 
tral mass of granite and granitoid gneiss, having its best exposures in Little 
Cottonwood Canon and the peaks to the south, and again in the Clayton’s 
Peak mass, where it rises like an island through the strata of the Lower 
Coal Measure limestone and the Weber quartzite. Plate I. is a view up 
among the summits of the Lone Peak mass, showing the rugged region near 
the head of a deep glacial canon. Although in Clayton’s Peak, and again 
near the lower end of Little Cottonwood Canon, the rock possesses ail the 
physical habit of a truly eruptive granite, and although in the Clayton’s 
Peak region the granite has undoubtedly been a centre of local metamor- 
phism and of metalization, yet, from the position of the overlying strata, 
a preponderance of evidence points to the belief that, whether eruptive or 
not, it is still of Archeean origin; hence its relations with the later stratified 
series are only those of rigid underlying masses, and the local metamor- 
phism observed in the limestones near the granites is strictly mechanical, 
and not to be mistaken for the caustic phenomena of a chemically energetic 
intrusion. It should be mentioned, however, that it possesses, both in its 
interior composition and in a peculiar conoidal structure, close affinities with 
the unmistakably eruptive granite of the Sierra Nevada; and it is quite 
possible that subsequent study will determine the presence here of two dis- 
tinct granites, the one having a regular bedding and belonging to the strati- 
fied Archzean series, the other of conoidal structure and eruptive origin. 
The main body extends about twelve miles northeasterly, from the trachyte 
slopes of the Traverse Hills to the head of Little Cottonwood Canon. Its 
greatest north-and-south expansion is through Lone Peak, a line about 
eight miles long. South of the mouth of Cottonwood Canon a narrow iso- 


lated patch of granite appears involved in the Archean schists. The Clay: 


46 SYSTEMATIC GEOLOGY. 


ton’s Peak mass, at the head of Cottonwood Canon, has an east-and-west ex- 
tent of about three miles, and runs the same distance north-and-south. Near 
the mouth of Little Cottonwood the granite breaks with a sharp fracture, 
possessing no bedding-planes and but a few irregular jointings. It consists 
of quartz, which is seen under the microscope to be remarkably poor in 
fluid inclusions, orthoclase, a relatively high proportion of plagioclase, 
biotite, large and brilliant black hornblendes, titanite, and microscopic 
apatite. For western granites, the titanites are particularly large, not infre- 
quently reaching one eighth of an inch in length. 

Passing up Cottonwood Canon, no sharp line of division between the 
structureless granite and the bedded gneissoid form is observable; but there 
appear gradually more and more planes having an easterly dip, until finally 
they approach the regularity of gneiss bed-planes, and the minerals are 
seen to possess a vague general parallel arrangement. ‘There is no essen- 
tial change in the mineral composition of the granite in passing from one to 
the other of these forms. If anything, titanite and hornblende are slightly 
less frequent in passing up the canon and into the region of bedded gneiss. 

The granite of Clayton’s Peak, however, has some essential differences. 
It is dark, very fine-grained, and carries a very large proportion of horn- 
blende and mica. Under the microscope the titanite crystals, which are 
present in large number, are seen to be much darker than in the other 
rocks. The feldspar and quartz, particularly the former, contain many 
microscopic impurities, chiefly plates of red and black oxyd of iron. The 
rock is proportionately rich in black magnetite grains, which penetrate the 
flattened crystals of apatite. The mineralogical differences through all 
these bodies of granite are indeed slight; changes of texture and arrange- 
ment produce a decidedly varying petrological effect, but in general they are 
granites, containing—besides the normal orthoclase, quartz, and biotite— 
plagioclase, hornblende, titanite, and apatite in high proportion ; all but the 
apatite being visible to the naked eye. 

The bodies of granite porphyry shown on the map in the neighbor- 
hood of Clayton’s Peak are in all probability a dependence of the granite. 
They are always rich in hornblende and orthoclastic feldspar, which throws 


them into the class of syenitic granite porphyries. The body which comes 


ARCHAAN EXPOSURES. AM 


to the surface in the bottom of Cottonwood Canon, two miles below the bend, 
is remarkable for the high proportion of pyrites, which has penetrated in 
fine grains through the quartz and feldspar crystals. A granite-porphyry 
body adjoining Clayton’s Peak on the north, and forming the divide between 
the head of Cottonwood Canon and Parley’s Park, is also richly impreg- 
nated with pyrites. Its groundmass is pale green, from the presence of 
epidote, here an alteration-product after hornblende, and is rich in plagio- 
clase. The larger feldspars, which are chiefly orthoclase, have a red color 
derived from a microscopic dust of iron oxyd. 

Lying to the west of the granite body of Little Cottonwood Canon, 
and occupying the extreme foot-hills, is a belt of Archean schists, varying 
from a mile to two miles in width, and extending from the Traverse Moun- 
tains north to the mouth of Cottonwood Canon. ‘The general strike of this 
body is northeast, with a dip of from 45° to 60° to the north and west. 
From 2,000 to 3,000 feet of schists and quartzites are laid bare. 

A very good exposure is found in the second small canon south of Cotton- 
wood, where an estimated thickness of from 2,000 to 2,500 feet of highly 
metamorphic slates rests directly on the granite. Overlying these is a zone 
of quartzites, the uppermost members of which are blue, very hard, and 
schistose. A great deal of local contortion is observed in the strata; in one 
place they completely surround a small knob of granite, which is probably 
a submerged portion of the spur running northwest from Twin Peaks. 
Among the lower horizons is found a green hornblende schist, rich in quartz. 
It is almost a quartzite, and is thickly penetrated by small bluish-green 
hornblende prisms, which give the rock its schistose cleavage. There is 
also a little brown mica. At the mouth of the Little Cottonwood this Ar- 
chzean zone is represented by about 1,000 feet of quartzites, which extend 
perhaps half a mile up the canon, making a junction with the granite body. 
South of the mouth of Little Cottonwood Canon the same quartzites extend 
down to the trachytes of the Traverse Mountains. In direct contact with 
the granite at the mouth of Cottonwood Canon is a development of mica 
schist. 

On Rhodes’s Spur, at the head of Cottonwood Canon, resting directly 
upon the granites of Clayton’s Peak, is a curious garnetiferous schist. It 


48 SYSTEMATIC GEOLOGY. 


is a coarse-grained quartz rock penetrated by delicate green fibrous epidote 
and carrying a very high proportion of brown crystals of garnet, which 
indeed make up the greater mass of the rock. Zirkel describes the gar- 
nets as showing under the microscope a peculiar schistiform structure, as if 
resulting from a continuous aggregation of layers. Besides the garnet and 
epidote, these rocks show an appreciable amount of specular iron and 
local concentrations of dark-green fibrous hornblende. Intermediate stages 
between the hornblende and the epidote are so evident that there can be 
little doubt that the latter is an alteration-product of the former. 

There are present in this neighborhood, then, two distinct families of 
rocks: first, the Archzean, consisting of schists and granites; second, the 
vast, conformable post-Archzan group of sediments. Wherever observed, 
the region of contact between the two families displays no marked meta- 
morphism on the part of the sedimentary series, and within the Archean 
series no such transitions as would lead to the belief that the granite is only 
a more highly metamorphic form of the crystalline sedimentary series; on 
the contrary, the contact is so clearly defined, and the rocks are mineral- 
ogically so dissimilar, that it is very evident that the granite is either an 
intrusive mass or else an original boss over which the Archzean sedimentary 
materials were deposited. While the granite itself bears a very close resem- 
blance to the Californian eruptive granites, its relation to the flexed Palzeo- 
zoic strata would indicate that they were bent around a solid body, not that 
a plastic granite intruded into the bent Paleeozoics. The absence of granite 
dikes penetrating the immense sedimentary series would strengthen the belief 
that the granite antedated it. It is also noticeable that the dip and strike of 
the Archean schists west of the granite body are entirely discordant with the 
overlying Cambrian series, the former striking northeast and dipping north- 
west, the latter striking northwest and dipping southeast, this unconforma- 
bility being preserved up to the contact. Supposing the whole Archzean 
body to have been thrust upward and eastward when the flexure of the 
Paleozoic series took place, the present dip of the Archzean schists and 
quartzites would indicate that before the great Wahsatch uplift they were 
in a nearly vertical position, flanked to the east by the granite mass. In- 


trusive dikes do in some instances cut the marbleized limestone, but they 


ARCILASAN EXPOSURES. 49 


are middle-age porphyries, not to be confounded with the Archzean crys- 
talline rocks. 

The next Archean body makes its appearance about eight miles north 
of Salt Lake City, in Sawmill Caton. Here the Paleozoic strata, uncon- 
formably overlying the Archean, trend diagonally in a northeast direction 
across the range. Irom the southern line of its outcrop the main mass is 
composed of an Archzean block extending 20 miles northward, and no doubt 
occupying the whole body of the ridge, except upon the eastern foot-hills, 
where it is overlaid by the beds of the Vermilion Creek Eocene group. 

There seem to be two distinct series within the Archzean mass, the earlier 
occurring only at the extreme southern end of the exposure, and confined to 
the spur between Sawmill Canon and that next north. Here is laid bare a 
small body of intensely metamorphosed material of an ashen-gray color, 
composed of quartz, orthoclase, and a very little muscovite. It weathers 
with an excessively rough surface, developing curious waving lines. It 
appears to have been a body of quartzitic schist, containing a little ortho- 
clase and mica, which has undergone the most violent compression and 
crumpling, obliterating entirely the original bedding and leaving only ob- 
scure traces of short, abrupt, and extremely irregular corrugations. North- 
ward, this body passes unconformably under the main series of gneisses 
and schists which form the range in that direction. The regular strike 
and dip of the gneisses and schists continue close down to the highly 
corrugated structureless body, but the exact contact was obscured by soil 
and a dense growth of scrub oaks. From the nature and position of the 
two bodies there is no doubt that they are actually unconformable, and 
that the bedded gneisses are the younger group. 

The later series consists of beds of gneiss, quartzite, and various 
hornblendic schists, forming a great conformable group which always dips to 
the west at angles varying from 15° to 40°, and is admirably exposed in 
the various canons which are cut down the two flanks of the range, and 
especially also in the transverse cut of the canon of Weber River, where 
the whole range is severed. The series is characterized by great chemical 
and usually mineralogical persistence of individual beds for comparatively 
long distances, and by the absence of any important minor corrugations. 

4k 


50 SYSTEMATIC GEOLOGY. 


The group forms a simple monoclinal ridge, dipping to the west at angles 
increasing from 15° at the south to 25° and 40° farther north in the region 
of Weber Caion, attaining still higher angles near Ogden. The trend of 
this series is somewhat sinuous. As developed in the summit rocks, from 
Sawmill Canon to Farmington Canon, the strike is about north 20° west; 
but near the head of Farmington Canon the line swerves rapidly to the east, 
passing to 10° east of north, whichit maintains for four or five miles, and then 
bends back again to the west, conforming with the strike of the southern 
portion from north 15° to 20° west. In the axes of these two bends of 
strike there is a good deal of local flexure and not a little dislocation. North 
of Farmington Canon, where a deep exposure occurs, there are from 12,000 
to 18,000 feet of conformable beds. Down the east slope of the range to 
the contact with the Eocene, the Archean rocks are still seen dipping to the 
west. Of course no estimate can be formed as to how much farther down 
beneath the overlapping Eocene sandstones the conformable Archzean series 
descends. The lowermost exposed members are of intercalated gneisses and 
hornblende schists, with minor beds of quartzitic schist carrying more or 
less feldspar. 

An interesting type of the coarse gneiss is observed near the head of 
Farmington Canon. It is composed of large crystalline masses of flesh- 
colored orthoclase and partially decomposed,earthy brown magnesian mica, 
with irregular bodies of pure, milky-white quartz. This stratum is interesting 
as showing the transition from an evenly bedded rock into a structureless 
one. The original sheets of mica may be readily traced, though at present 
they all bend into wavy lines through the mass of the bed, or, what is rather 
less common, mica flakes all arrange themselves on a diagonal to the plane 
of the bed. Tracing this bed a few miles north from Farmington Cation, 
the minerals are observed to be less and less disturbed, and finally not a 
single mica flake deviates from its original parallel position. Such changes 
as this are frequently observable in gneiss beds; but it has nowhere been 
the fortune of this Exploration to observe those peculiar rapid transitions 
from one species of rock to another which are so constantly to be found in 
descriptions of Archean schists and gneisses. On the contrary, all the 
observations of this corps tend to prove that there is a remarkable perma- 


ARCHAAN EXPOSURES. bil 


nence of chemical make-up within each bed, and that the only changes 
which take place within a given stratum are through the hydration of 
some of the contained species, or else mere physical changes in the rela- 
tive arrangement of the species. A mica schist passing into a hornblendic 
schist, or a hornblendic schist into a granite, or a gneiss rock into an argil- 
lite, along the line of their longitudinal extensions, are phenomena which 
failed to appear on the Fortieth Parallel. It is believed that such observa- 
tions, not at all infrequent in certain accounts of western geology, betray 
a talent for fiction which might find a more appropriate field within the 
domain of romance. While individual beds extend for great distances with- 
out chemical change, on the other hand in descending or ascending through 
the series there is the greatest variety of changes, every combination pos- 
sible to the few mineral constituents being repeatedly illustrated. 

Over these coarse Farmington gneisses are a series of fine gray gneiss, 
in which the feldspar and quartz are both white, and the mica muscovite. 
It is a rock made noteworthy by the presence of freely disseminated minute 
garnets, which Zirkel has shown under the microscope to be riven in every 
direction by infinitesimal cracks, and to be more or less altered into chlorite, 
sometimes attaining the complete pseudomorphism which has been so inter- 
estingly elaborated by Prof. Raphael Pumpelly in his description of the 
rocks of Lake Superior. 

A little higher in the series is another gneiss, still containing a predom- 
inance of white mica (muscovite), but with a little hornblende. It is also 
rich in garnets, which likewise show the transition into chlorite. For a 
full account of the minute method of this pseudomorphism, the reader is 
referred to the pages on Archzean schists in Volume VI. of this report. 

Above these is a heavy group of dark-green hornblendic gneisses, 
rich in feldspar and apatite ; besides which, Zirkel has identified under the 
microscope a considerable proportion of zircons. They are never large 
enough to be visible to the naked eye. In the zirconiferous gneisses the 
hornblende is always more or less fibrous, from dark-green to black, and 
arranges itself with the broader surfaces of the prisms coincident with the 
bedding-planes. Quartz and feldspar hold a very variable position in this 
series, as they do in the hornblendie rocks of Medicine Bow and Park 


52 SYSTEMATIC GEOLOGY. 


ranges. There is every variety here, from a pure amphibole, containing 
sparse grains of quartz but no feldspar, to beds in which either quartz or 
feldspar largely predominates, and in which hornblende plays a very insig- 
nificant part. Apatite is characteristic of those rocks in which mica does 
not exist. There are no means of closely determining the relative thick- 
ness of the various types of crystalline schists which repeatedly recur in 
this body. But it is evident that only the lower members are true gneisses, 
while by far the greater part represents a varying association of hornblende, 
feldspar, and quartz. ‘There are narrow zones which may be called quartz- 
ite, though carrying not a little feldspar, but no large, true zone of pure 
quartzite. The most noticeable fact is the sequence of richly feldspathic 
eneisses and mica eneisses containing garnets, the two overlaid by a large 
series, which is prevalently hornblendic, but carries more or less zircon- 
iferous beds. This seems to be a very nearly direct repetition of the se- 
quence in the Rocky Mountain system, and of one which will be described 
hereafter in Humboldt Range. 

Four miles north of the canon of Weber River, the Archeean series is 
lost by passing under beds of the Paleozoic series. Two miles south of 
the mouth of Ogden Canon it reappears, coming out from under the Cam- 
brian quartzite, and it is exposed along the western foot-hills of the range in 
a zone about four miles long by half a mile to a mile wide. On the west it 
is bounded by the Terrace formation, and along the east it passes uncon- 
formably under the quartzites of the Cambrian. The rocks of this exposure 
are an intimate association of dark reddish-gray and dark-red gneisses, 
in which hornblende largely predominates over mica. Mica is variably 
present, but never reaches a high proportion, and is sometimes altogether 
absent. Both orthoclase and plagioclase are present, the latter predom- 
inating. Quartz occurs freely, sometimes segregating itself into sheets of 
pellucid grains. Zirkel describes a very interesting arrangement of the 
mica, seen only under the microscope, as well as the occurrence of apatite 
and zircon. The interesting method of isolating and determining zirconium 
in these rocks, as devised by Mr. R. W. Woodward, the chemist of this Ex- 
ploration, will be found detailed in Volume II.,Chapter III, under the ac- 
count of Wahsatch Range. His method depends on the insolubility of zircon 


ARCHASAN EXPOSURES. 53 


in hydrofluoric acid. Every variety of structure is noticed in this exposure 
of hornblende rocks, ranging from distinct lamination, in which the horn- 
blende crystals are arranged in sheets separated by zones of feldspar and 
quartz, to a structureless condition in which the rock rich in plagioclase and 
hornblende might easily pass for an eruptive diorite. As a whole, they 
have a strike of about north 20° west, with a high dip to the west. Their 
unconformability with the overlying Cambrian quartzite is well shown 
along the whole front of the range, from Ogden Cation to Eden Pass. 

Directly north of Ogden’s Hole, occupying a geological position simi- 
lar to that of the last-described exposure, unconformably under the Cam- 
brian quartzite, is another Archean body. At its extreme northern end, 
four miles south of Brigham City, the Cambrian disappears and the Silurian 
limestone comes directly in contact withthe Archean. Here also the rocks 
strike about north 20° west, and dip at a high angle to the southwest. They 
consist of a series of micaceous and hornblendic gneisses, having rather a 
granitoid appearance, but for the most part clearly displaying the planes 
of bedding. A very characteristic hornblende gneiss is collected near the 
south point of the body, and consists of coarse-grained orthoclase, a compar- 
atively large amount of plagioclase, quartz, a little brown mica, and much 
hornblende. Apatite is discovered under the microscope. Among the upper 
dioritoid beds are some which are decidedly poor in hornblende, but carry 
well developed microscopical crystals of zircon in considerable frequency. 
Almost all the lower members of the Ogden Point series are more truly 
gneissic than the upper ones. 

It is very clear that the three last-described exposures—the great body 
forming the range from Ogden Peak south to Sawmill Canon, the narrow 
body at the mouth of Ogden Canon, and the exposure north of Ogden’s 
Hole—are all parts of a single series, having a more or less flexed but 
generally northwest strike, accompanying the general trend of the range, 
and all dipping conformably to the west. Their contact with the overlying 
Palzeozoic rocks varies from the Silurian limestone to a horizon 3,000 or 
4,000 feet down in the Cambrian quartzites. It is further evident that when 
the easterly dipping Paleozoic rocks were ina horizontal position, the west- 


erly dipping Archzean beds would stand at a much higher angle ; and, com- 


54 SYSTEMATIC GEOLOGY. 


paring the points of contact between the Archzan and the Paleozoic, it is 
clear that the summit profile of the original Archean ridge was eroded into 
peaks rising at least 4,000 feet above the general outline of the ridge, and 
that these peaks were not abrupt, but were rather gently rising domes. 

ArcH&AN oF Satt Lake anp THE PromonTory.—Promontory Range, 
which projects southward into Salt Lake, has exposed upon its southern 
extremity a body of slates and quartzites, together with minor hornblendic 
and mica schists. About five miles south of Promontory Point, on the trend 
of Promontory Range, lies Frémont’s Island, which may be considered as a 
part of the same development of Archzean rocks. Still farther south, Ante- 
lope Island, a body of land twelve or fourteen miles in length by four miles 
in width, whose longer axis points northwest, seems by its material and posi- 
tion to be a southward continuation of the same Archzean mass. West of 
Ogden City, at the landing rocks northwest of the mouth of Weber River, 
there is also a slight development of westerly dipping Archzean schist. ‘This 
latter exposure is surrounded by the mud beds of the lower Quaternary 
desert formation, and is of very slight importance. The two above-men- 
tioned islands and the southern point of Promontory Range, taken together, 
represent a body chiefly composed of argillaceous, pyritiferous schists, mica 
schists, and granitoid gneisses, which, according to the accounts of Stans- 
bury and the slight notes of our own topographer, appears to dip west on 
Antelope and Frémont islands, with a general northwest strike; while on 
the point of the promontory it is much more disturbed, but has, however, 
a prevalent northeasterly dip, with a northwest strike. The trend of these 
masses, if continued southward, would carry the body under the western 
side of Jordan valley. It would seem as if Promontory Range, the two 
islands, and the Oquirrh represent a range in a measure comparable to the 
Wahsatch, formed of an Archzean core and an overlying folded Palaeozoic 
series. 

Rart River Mountarins.—North of Bovine Station, where the Central 
Pacific Railroad skirts the northern edge of Salt Lake Desert, rises the 
southern group of Raft River Mountains, a range which trends north- 
ward and extends beyond the limits of Map III. In the middle of the 


ridge, at Citadel Peak, and extending thence along the eastern side of the 


ARCHASAN EXPOSURES. 55 


range for ten or twelve miles, is a triangular exposure of granite, the west 
and south sides wrapped around and overlaid by limestones, which have 
been referred to the horizon of the Lower Coal Measures. Quaternary 
beds skirt the eastern base of the granite, which here forms the foot-hills of 
the range. The topography is a series of irregular parallel ravines, eroded 
from west to east. Citadel Peak, the highest summit, reaches 2,500 feet 
above the level of the desert. The Quaternary of Clear Creek valley pen- 
etrates the range, isolating a northern mass of granite from the main body, 
as will be readily seen upon the map. The rock is nearly structureless, the 
few jointing-planes showing no indications of a parallelism which would sug- 
gest a gneissoid structure. It has a uniform and medium texture and a pearl- 
gray color, and is composed of quartz, orthoclase, and mica. The granite 
malady has taken hold of the surface very generally, and it is covered with 
crumbling débris. The main spurs and ridges present everywhere smooth, 
round outlines, with many small, fanciful forms of erosion. 

Desert Granite Rance.—About 25 miles west of the Cedar Moun- 
tains, and a few miles south of the southern limit of our Map IIL., is a nar- 
row ridge extending on a north-and-south trend eight or ten miles, and 
scarcely more than a mile or a mile and a half in width. From this con- 
tracted base it rises fully 3,000 feet above the level of the desert. The northern 
half, where examined, consists exclusively of a variety of granite having < 
decidedly metamorphic habit, although the bedding-planes were not dis- 
tinct enough to give a definite idea of the true orographical structure. In 
general, it is a fine-grained, nearly white mass, sometimes changing into a 
coarse variety in which the mica plates reach an inch in diameter. The 
central heights are intersected by veins of a dark-green hornblendie granite, 
which under the microscope is seen to contain very little unaltered horn- 
blende, but a dichroitic green chlorite-like mineral, besides considerable 
dark hexagonal mica, titanite, and apatite. Its quartz and feldspars are rich 
in fluid inclusions. <A gray variety, of medium-sized grains, contains both 
black and white mica. The fine-grained white varieties hold only white 
mica, quartz, and orthoclase, with a few scattered particles of the chlorite 
mineral, no biotite, titanite, and very little apatite and plagioclase. 

Goosr Creex Hitis.—In the northeast corner of Map IV., directly 


56 SYSTEMATIC GEOLOGY. 


west of the 114th meridian, is shown the southern termination of the Goose 
Creek Hills. Near the western foot-hills, at the head of the east fork of 
Passage Creek, is exposed a small body of granitic porphyry, occurring in 
some of the deeper ravines under limestones and quartzites which have been 
referred to the Carboniferous. In a fine-grained groundmass, consisting of 
hornblende, orthoclase, plagioclase, and quartz, are embedded large crystals 
of feldspar, which for the most part are altered into an opaque mass, showing 
under the microscope that they are mainly monoclinic, but in exceptional 
crystals displaying the traces of a former striation. In some of the earthy, 
decomposed feldspars are colorless acicular crystals referred to muscovite. 
Zirkel calls attention to the hornblende as noteworthy for presenting, as 
a product of decomposition, black, opaque, angular grains, which are doubt- 
less magnetite, but which do not occur in the fresh, undecomposed horn- 
blende. These porphyry outcrops are too limited to indicate anything about 
the structure of the mass. 

OmbBe Rance.—In Ombe Range, about half-way between Pilot Peak 
and Lucin Station, there is a gentle depression or pass traversing the range 
from east to west. The hills to the north are composed of Upper Coal 
Measure limestones, reposing conformably upon a heavy development of 
the Weber quartzite, the whole series resting unconformably upon a granite 
body which appears exposed to the pass. The high hills southward, to 
Pilot Peak and beyond, are altogether made up of Weber quartzite. The 
exposure of granite in the pass is only about four and a half miles from 
east to west and two and a half miles from north to south. On the west 
the granite sinks under Quaternary slopes of Salt Lake Desert. 

In so small a block, little can be learned of the structural relations 
of the granite, except that it is distinctly unconformable with the overlying 
sedimentary series. Since at least 3,000 feet of quartzite are in contact 
with the granite, and also a considerable thickness of overlying limestones, 
it would be evident that the topography of the original granite mass over 
which the sedimentary series was superposed possessed slopes of at least 
4,000 feet. The granite mass may be considered a part of an underlying 
range, which was crowded up when the Paleeozoic rocks were tilted, its rigid 


body perhaps determining the axis of the modern anticlinal. Irom so 


ARCHAAN EXPOSURES. 57 


limited an outcrop it is impossible to decide between a metamorphic and an 
eruptive origin, but there is an absence of all appearance which would lead 
to the belief that it is metamorphic. The granite itself is a medium-grained 
but somewhat friable rock, of a mottled gray and red color, made up of 
quartz, large masses of white orthoclase, and a reddish triclinic feldspar. 
Mica in thin brown flakes is present, not infrequently adhering to the thick 
broad faces of the orthoclase. It is, however, an unimportant constituent. 
A determination of the alkalies of one of the white orthoclases gave, soda 
.34, potash 12.58. 

Gostutr Raner.—In Toano Pass, about four miles south of Fairview 
Peak, occurs a small, obscure mass of granite. It has a friable, much de- 
composed surface, and betrays no distinct lines of bedding. Like the pre- 
viously described granite, it is composed of quartz, orthoclase, sparing 
plagioclase, and a little mica Its only geological interest is its accidental 
exposure in a deep pass. The region north of the old Overland Road, 
between Salt Lake Desert and the Humboldt Mountains, only shows its 
granites in inferior geological situations, as in passes, and it is usually 
evident that the exposed mass is the summit of a submerged range laid bare 
by erosion in the axial part of a fold, or brought to the modern surface by 
some extended fault. 

About fifteen miles south of Toano Pass the hills of Gosiute Range 
fall away into a broad open pass, but rise again southward toward Pine 
Mountain. The Quaternary of Tacoma and Gosiute valleys sweeps up 
from the east and west well into the pass, covering the lower slopes of a 
granite mass. As at Patterson Pass, this depression is occupied by a body 
of granite overlaid by quartzitic series referred to the Weber period. ‘The 
summit of the pass is about 500 feet above the Gosiute Valley and 1,500 
feet above that of Tacoma, the two valleys having about 1,000 feet dif- 
ference of level. The granite is rather coarse-grained, with loose, friable 
texture, and of a prevailing gray and yellowish-gray color. There are here 
again no appearances of a distinct bedding, nor do the constituent minerals 
show any gneissic parallelism of arrangement. The whole topography 
and lines of drainage show the rounded forms common to easily disinte- 


grated rocks. 


58 SYSTEMATIC GEOLOGY. 


Peoquop Ranee.—Fifteen miles southwest of Middle Pass, there is a 
similar depression in the Peoquop Mountains, in which a still narrower and 
more limited development of granite is exposed. The pass, which nowhere 
rises more than 500 or 600 feet above the level of the valleys on either 
side, is restricted to a width of about two miles, the Quaternary rising on 
either side against the granite slopes. As in Middle Pass, the granite is 
overlaid unconformably by Paleozoic strata, that to the north being of 
Weber quartzite, while to the south the limestones of the Upper Coal 
Measures appear. In structure, in mode of weathering, and in lithological 
character, the granite is similar to the limited areas just described. 

Taken together, the small granite exposures in these four passes possess 
interest solely on account of their position. As exposures of granite in a 
petrological way they are quite insignificant; but they are of the utmost 
importance as suggesting the topography of the underlying Archean forma- 
tion of this region, since they occur at points in the axial region of modern 
ranges and at points of deepest exposure. The significance of this will be 
shown in the concluding pages of this chapter. It is only necessary to 
say here that the position and character of these buried Archean ranges 
have given importance and direction to the subsequent orography. 

At Spruce Mountain there are some mica schists and slates which 
doubtless belong to the Archean series. ‘heir geological relations are 
quite obscure, and the exposure is so small as to be of comparatively little 
importance. Lithologically, they seem to be more nearly related to the 
schists of Humboldt Range than to those of any other locality. Indeed, 
they are only separated from the mass of Mount Bonpland by a single valley. 
The schists and slates are all distinctly bedded, are often finely laminated, 
and have always a ready cleavage. <A characteristie specimen represents a 
silvery-white rock, composed of minute granules of clear quartz and small 
flakes of mica—both biotite and muscovite, but no hornblende. Under the 
microscope, however, Zirkel detected an abundance of crystals of zircon, 
which, though plentiful in series of Archzean gneisses and schists, are usually 
observed in connection with hornblende. Moreover, the biotite plates con- 
tain exceedingly minute microscopical needles, which Zirkel also considers 


referable to zircon. Coarser and more loosely compacted schists are also 


ARCHAAN EXPOSURES. 59 


observed in the series. It is quite possible that further observation would 
confirm the presence of larger masses of Archzean than are now known 
along the foot-hills of this group. 

Tue Wacuoge Mountains. 
latitude about 40° 18’, rises an irregular group of mountains, whose main 


Between Gosiute and Steptoe valleys, in 


mass is composed of a granite nucleus, which is penetrated and surrounded 
by numerous modern outflows of Tertiary volcanic rocks. Granite gives 
shape to the northern mass of the range; the foot-hills to the south are 
made of a broad flow of rhyolite. Along the southern slope of the main mass 
is. a development of limestone, extending four or five miles ina northwest- 
and-southeast direction, which is referred by Mr. Emmons to the horizon of 
the Lower Coal Measures. The usual distinct nonconformity is observed 
between the sedimentary and the granite mass. The main body of granite 
extends eight or ten miles in a north-and-south direction, with about four miles 
of lateral exposure in an east-and-west line. On the west side it descends 
rather abruptly under the Quaternary plain; along the east more gradually, 
and here it is interrupted by outflows of porphyry, andesite, and rhyolite. 
The top of the highest granite peak is about 2,000 feet above the Gosiute 
desert. From the family of granites which appear in the low passes lately 
noted, this granite differs in many interesting ways. Although topograph- 
ically it gives rise to dome-like and gently rounding forms, there is not the 
same tendency to local disintegration which is observed to the north, and in 
consequence but very slight accumulations of granitic gravel upon the 
surface. ‘Transportation seems fully to equal disintegration, so that the 
slopes are pretty hard and bare. Aside from certain irregular jointing- 
planes, there appears to be no distinct bedding, nor even any noticeable 
parallelism in the jointing-planes. As a mass, it is far removed from those 
granites which have been treated as of metamorphic origin. The configu- 
ration of the mountain group and the character of the granitic slopes, as 
well as the interior arrangement of the mineral constituents, combine to 
impress a belief in the eruptive origin of the mass. The rock is of a dark- 
yellowish or reddish-gray color, passing into lighter shades on the northeast 
spurs and foot-hills, owing to a diminished proportion of mica and horn- 


blende. Quartz, orthoclase, plagioclase, and mica are the essential ingredi- 


60 SYSTEMATIC GEOLOGY. 


ents. In addition, there is a variable though large proportion of hornblende, 
and also afew dark granules which have been referred to specular iron. An 
appearance of cloudy impurity in the feldspars is seen microscopically to 
be due to the liberal inclusion of specular-iron grains and shattered frag- 
ments of hornblende and mica. A certain opaque dullness characterizes the 
general aspect of the feldspars. A few of the larger orthoclases have a bril- 
liant vitreous lustre. The mica appears for the most part in smooth, well 
preserved plates of dark biotite. There are also flakes of a bronze color, 
which are referable to phlogopite. Under the microscope Zirkel detects 
titanite and apatite, the latter in short, thick prisms, which are rich in fluid 
inclusions whose mode of arrangement is perpendicular to the main crystal- 
line axis. Salt cubes are also observed in the fluid inclusions of the quartz. 
Isolated from all our other granite areas geographically, it also stands alone 
as regards its chemical composition. Aside from the high proportion of 
titanite and apatite, and the inclusions of specular iron in the feldspar, it is 
closely related to the granites of the Sierra Nevada and of the Wahsatch. 
But by the extremely high proportion of mica and hornblende, the chemical 
analysis runs down to 55 per cent. in silica, a point lower by from 12 to 20 
per cent. than in any of the other granites of the Fortieth Parallel. From 
their extremely earthy appearance it would seem that the feldspars also 
may fall below their normal equivalents of silica. This must always remain 
one of the most interesting granite localities of the Cordilleran system. Its 
only described parallel in Europe is the granite of Adara, in Donegal, Ireland. 

Newr the north base of the northern hills, the granite is cut by an 
irregular dike of a fine-grained dioritic porphyry having a purplish-gray 
color. It is a dense, compact rock, angular in its fracture, with a highly 
crystalline groundmass, in which are embedded both orthoclase and plagio- 
clase; the latter, assumed to predominate, occurring as brilliant acicular 
needles. Fine fibrous green crystals of hornblende are pretty uniformly 
distributed through the whole mass. 

Kiystey Distrrict.—Southeast of the Wachoe Mountains, nearly in 
the middle of Gosiute Valley, is a north-and-south ridge connected by a 
low depression with the range to the west. It is composed of granite, 


eranitic porphyries, and Archean limestone, overlaid upon the west by 


ARCHAAN EXPOSURES. 61 


limestones of the Lower Coal Measure horizon, which dip to the south and 
west. Southward the Archzean and Carboniferous are bounded by rhyolite 
hills. The Archean series is made up, besides a limited boss of granite, of 
interbedded white crystalline dolomites and broad tabular masses of granitic 
porphyry. The conformably dipping series strike north and incline to 
the east about 25°. This interesting intercalation is well shown at 
Marble Hill, where no less than six different beds of the porphyry were 
observed between dolomitic limestones. The marble of all these beds is 
a remarkably pure, white, fine-grained, crystalline rock, approximately a 
dolomite, which upon analysis yields, carbonate of lime 56.54, carbonate 
of magnesia 41.12. Under the microscope the marbles are a ecrystalline- 
granular mass, the crystals of calcite having distinct striation, and carrying 
fluid inclusions. In appearance and in chemical nature they are closely 
allied to the dolomitic limestones of the Humboldt Range Archzean series. 
The intercalated granite porphyries consist of a rather homogeneous and com- 
pact groundmass approaching felsite in composition, in which are many 
grains of limpid quartz. The feldspars are very much altered, representing 
every grade of decomposition, from purely kaolinized bodies to quite unal- 
tered crystals, some of which possess distinct triclinic striation, while others 
are clearly orthoclase. Hornblende occurs both porphyritically enclosed 
and as minute fibres in the groundmass. Large plates of deep-black mica 
are present, and are frequently pierced by microscopic apatite. In those 
varieties of which the groundmass is coarse-grained, microscopical titanite 
and well crystallized magnetite have been observed. Under the micro- 
scope the quarizes are seen to contain ragged inclusions of the ground- 
mass. There are also many empty cavities and fluid inclusions, among 
which are some with liquid carbonic acid. There are, however, no glassy 
particles. A small body in the northern part of the ridge, colored as gran- 
ite, is a microgranitic matrix, which contains brown mica, well defined 
needles of hornblende, rounded quartzes, and partially decomposed feld- 
spars. 

There is room for considerable difference of opinion as to the nature of 
these granitoid porphyries. Their direct interstratification with the marbles 
confirms the probability of their being metamorphic. When we compare this 


62 SYSTEMATIC GEOLOGY. 


locality with the marble region at the top of Mount Bonpland in Humboldt 
Range, the limestones there are seen to be separated by beds of quartzite, 
and of rather porphyritical gneiss, which are not far removed from the 
interbedded porphyries of the Kinsley District I feel no hesitation, there- 
fore, in assuming that these almost typical rocks are only a more highly 
developed gneiss-porphyry, and are equivalents, in petrographic make-up 
as well as in age, of the Mount Bonpland intercalations. 

Franxuin Burres.—In longitude 115°, directly west of the northern 
end of Egan Range, are three isolated buttes rising out of the Quater- 
nary plain. The extreme eastern foot-hills of the easternmost elevation are 
formed of limestones of the Lower Coal Measure period. Otherwise, with 
the exception of a small diabase dike in the middle butte, the three masses 
are composed of granite and granitoid rocks, which are chiefly of porphy- 
ritical habit, the latter closely resembling the porphyries of the Kinsley 
District. In the middle and western butte are true syenitic granites, con- 
sisting of quartz, the two feldspars (the predominating orthoclase flesh- 
colored, and the plagioclase greenish-white), bright, well crystallized horn- 
blende, and titanite, which is often visible to the naked eye. There is no 
mica. For microscopical details the reader is referred to Zirkel’s interest- 
ing memoir. 

Houmpotpr Raner.—In the middle of Map IV. appears the most promi- 
nent mountain mass in eastern Nevada. It is called Humboldt Range 
from its northern extremity as far south as Hastings’s Pass, a distance 
of about 85 miles, and beyond that point receives the name of White 
Pine Mountain. The average trend is about north 18° east. Between 
Frémont’s and Hastings’s passes the main mass of the ridge is made up 
of easterly dipping Paleozoic rocks from the Ogden Devonian group 
up to the Lower Coal Measure limestones. North of Frémont’s Pass 
it is essentially an Archzean body, flanked in a few localities by the rem- 
nants of upturned Paleozoic beds, which rest unconformably upon the cen- 
tral core of the range. With the exception of a small body of granite 
extending from Frémont’s Pass a little north of Lake Marian, the whole 
Archzean series is made up of a body of conformable and westerly dipping 
gneisses, gneissoid schists, hornblendic and in some instances dioritoid 


ARCHAAN EXPOSURES. 63 


schists, dolomitic limestones, and quartzites. Throughout its eastern side 
the range is bordered by a Quaternary valley, in which are three promi- 
nent depressions, occupied by Eagle, Franklin, and Ruby lakes. The 
entire western base of the range is overlaid by the horizontal beds of the 
Humboldt Pliocene series, which were deposited in a long northeast-and- 
southwest lake, occupying the whole of Huntington and Upper Humboldt 
valleys. The range is, therefore, detached from all other rocks earlier 
than the Pliocene, and its geological connections with the neighboring 
ranges can only be established inferentially. The fragments of Palzeozoic 
rocks which skirt its western base at two or three points north of Frémont’s 
Pass dip westwardly, while the large series of Paleeozoic limestones and 
quartzites dip eastwardly. Both sets of Paleozoic strata rest unconform- 
ably upon the Archean. The northernmost extension of the easterly dip- 
ping limestones curves from a gentle dip of from 16° to 20° east up to the 
vertical, near the base of White Cloud Peak. While no easterly dipping 
Archean strata are exposed in the whole range, yet the anticlinal position 
of the two limestone series shows that a fold has taken place diagonally to 
the range, and the rapid increase of angle of the easterly dipping limestones 
indicates that the displacement along this axis was increasingly great toward 
the north. It is also observed that the eastern face of the Archean part of 
the range north of White Cloud Peak is very abrupt, displaying either 
extremely metamorphic granitoid forms, or the edges of westerly dipping 
Archean crystalline schists. By the entire absence of easterly dipping 
Archean and of easterly dipping Palzozoic rocks north of White Cloud 
Peak, it becomes evident that a fault similar to that of the Wahsatch has 
cut down the core of the range from north to south, and that the eastern 
half north of Frémont’s Pass is depressed below the level of the Quater- 
nary plain. Unfortunately, the projection of Archzean directly east of 
Eagle Lake was not visited; and it remains uncertain whether this may 
not be a fragment of the eastern half. The writer has only examined the 
granites of the Frémont’s Pass region, northward to the region of White 
Cloud Peak, where it is impossible to determine whether they are conform- 
able or unconformable with the overlying westerly dipping crystalline 
schists. By the entire absence of any distinct and persistent planes of bed- 


64 SYSTEMATIC GEOLOGY. 


ding, this granite bears an evident resemblance to the eruptive type. But 
there is a series of obscure planes, which strike with the range and dip 
west, dividing the mass into tabular layers which vary from 40 to 80 feet in 
thickness. This broad parallel formation only becomes apparent to the 
eye in the field. Hand specimens fail to show any characteristic differ- 
ences between successive beds. A greater or less proportion of mica gov- 
erns the appearance of these tabular masses; and the distinction is rather 
based upon the degree of whiteness which they show. The rock itself 
is composed of two types of quartz—a pellucid, white variety, and an 
equal amount of a smoky kind. There is orthoclase and _ plagioclase, 
the former decidedly predominating, while the microscope reveals apa- 
tite, whose prisms occur very plentifully, traced lengthwise, parallel with 
the direction of the micas. These are sometimes conspicuously flattened, 
and again they are broken into disconnected sections. Hornblende is 
entirely wanting, but zircon is abundant under the microscope. It cannot 
be said that the micas are parallel; that is to say, the flat plates are not 
arranged with parallel edges, but the longer axes of almost all the mica 
particles are in one direction, which gives the rock an indistinct but unmis- 
takable appearance of parallel arrangement. The same obscure linear 
arrangement is observed in the feldspars and quartzes, yet this is not suffi- 
ciently distinct to give the rock at all the appearance of a gneiss. The 
triclinic feldspars are fresh, creamy-white albites, and resemble some of 
those found in Californian granites. This is one of the few occurrences 
we have of zircon in a rock entirely without hornblende. 

From 1,000 to 1,500 feet below the summit, down the west side of 
White Cloud Peak, a decided change takes place in the rock, and the granite 
passes under the true gneissic series. Southward along this granite there 
is a decided change, and in the region of Frémont’s Pass it is coarser and 
more truly structureless, yet the composition is the same, even to the zircon; 
and owing, first to the broad bedding above described, and secondly te the 
obscure parallel arrangement of the mineral constituents, I am inclined to 
throw this into the metamorphic type of granite. It bears a singular re- 
semblance to some of the Huronian granitoid rocks of Canada, also con- 
ceived to be metamorphic. Northward, between Overland Ranch and 


‘ 
. 
ta 
sk 
4 
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ri 
—— 
- 
“9 
’ 
_ 
’ 
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= Fi 
! 
od ce 
> - - 


ARCHAAN EXPOSURES. 65 


Sacred Pass, the eastern front of the mountain is an abrupt mural face, and 
is made up of varying masses of granitoid rock possessing always more or 
less traces of gneissic structure. With local exceptions in what seemed to 
be northward prolongations of the Frémont’s Pass granite, making up in 
dome-like masses into the crystalline schists, the whole Archean body of 
the range is distinctly a bedded series. In Sacred Pass, upper members of 
the Lower Coal Measures are seen to rest directly and unconformably upon 
the schists, while to the south, east of Camp Halleck, towers above them a 
group of high schist peaks. The sudden and commanding lift of these 
Archean peaks, above the point of contact with the limestone, and the rapid 
overlap of the uppermost Paleozoic strata concealing lower members of the 
series, clearly indicate high primitive Archean peaks around which the 
limestones were deposited. 

Plate II. shows Lake Marian, a glacial bowl northwest from Overland 
Ranch in the heart of a group of granite crags, at an altitude of above 
10,000 feet. Plate IV. is a look into one of the 2,000-foot glacial troughs 
wrought out of the rocks of the same region, but on the west slope, back of 
Camp Halleck. 

South of Sacred Pass, among the schists, hornblendic varieties and 
quartzitic schists bearing mica predominate upon the outer flanks of the 
mountain. In the lowest horizons, as exposed in the deep glacial canons, 
granitoid gneisses, gradually approaching the structureless form, are ob- 
served. They vary in their westerly dip from 20° to 40°. The gran- 
ites before described appear to underlie conformably, and may, upon 
future study, prove to be only the lowest lying and most extremely meta- 
morphosed of the series. At the head.waters of the South Fork of the 
Humboldt, a bold mountain promontory makes out from the range, extend- 
ing westwardly twelve miles from the summit, and displaying about its 
base a margin of Devonian and Lower Coal Measure limestones, which are . 
wrapped around the Archean convexity in the shape of a horseshoe. The 
mass of the promontory itself is of heavy Archean quartzitic schists, inter- 
stratified with micaceous and hornblendic beds, hornblende predominating. 

Both the east wall of the northern part of the mountains, and the deep 
cafions which are carved down from Mount Bonpland to the western foot of 


5K 


66 SYSTEMATIC GEOLOGY. 


the range, offer the best exposure of Archzean rocks. At its base the series 
is seen to be formed of mica gneisses of a bright-gray color and very great 
variety of texture and habit, made up of an association of quartz, black and 
brown micas, and a very variable quantity of orthoclase and plagioclase. 
Of the whole 8,000 or 10,000 feet, perhaps the lower 5,000 feet are predom- 
inantly micaceous, a few narrow zones of quartzite lying within the gneiss, 
but the upper members, while containing a few sheets of typical mica gneiss, 
are chiefly of hornblendic and dioritic schists, which are interesting on 
account of the number of minerals they contain. Plagioclase prevails over 
these hornblendic beds, but both feldspars are always present. Mica, too, 
frequently occurs, but it is of a dark earthy brown. The predominant 
hornblende is a dark-greenish black or a pure black. Apatite and titanic 
iron are very frequent constituents, but are only observable under the 
microscope. Enclosed between some of the upper beds of gneiss, which are 
rich in orthoclase and poor in mica, are some sheets of pure amphibole, 
which are noticeable as containing no other minerals whatever, not even 
microscopic quartz or feldspar. 

A very interesting form of gneiss is found on the west slope of the 
‘ange, just below Clover Peak. It is a fine-grained, brilliantly gray rock, 
in which the white particles of quartz and the black micas have a granitoid 
arrangement; but the rock at large has a distinctly fissile structure, and 
cleaves easily in sheets of an inch or more in thickness. Besides the hex- 
agonal biotite, there are frequent plates of a brilliant coppery-bronze ortho- 
rhombic mica, and the rock is further distinguished under the microscope by 
containing a great deal of very fine zircon. It is also variably clouded and 
stained yellow and brown by infiltrated oxyd of iron. The planes which 
produce the fissile structure are developed by a parallel arrangement of 
bronzy micas, whereas the solid uncleavable sheets themselves contain 
biotite and phlogopite, but arranged without any attempt at parallelism. 
Mica sheets which define the cleavage-planes show a gently undulating 
surface and many marks of attrition, as if the rock had been subjected to a 
severe strain and had given way everywhere in a slight interior movement. 
Throughout the whole formation, with the exception of dioritic gneisses, 


quartz predominates over the feldspars in quantity. In general there is 


af 


VMS 


it 


op AG 


# 


ARCHAMAN EXPOSURES. 67 


more orthoclase than plagioclase when associated in the rock with mica, 
but in the presence of much hornblende plagioclase takes precedence of 
orthoclase. These gneisses are particularly instructive as to an interior 
change, probably due to pressure, which broke up the parallel structure of 
micas and hornblendes, resulting in a gradual approximation toward the 
granite form. As a general rule, the more the parallelism of the micas and 
hornblendes is broken up, the larger individual feldspars, particularly pla- 
gioclases, are developed. This whole change seems to have been brought 
about by longitudinal compression of the beds. At present the rock 
cannot be distinguished, in hand specimens, from a granite, except that 
there is even yet an indistinct cloudy parallelism of its dark constituents. 
Between this stage and the true schistose gneiss, in which all micas are 
strictly parallel and no crystals of quartz or feldspar break through the 
mica layers, there is every possible transition. The first symptoms of 
change are observed in a wavy arrangement of the micas. When carried 
a little farther, these wavy lines are broken and distorted. Feldspar crys- 
tals and grains of quartz are thrust in, breaking the continuity of the mica 
lines. Signs of compression are then visible in the squeezing of interstitial 
quartz and feldspar into a confused mass wholly devoid of parallel arrange- 
ment. In this condition also it is observable that all the crystalline particles 
of the rock, notably the micas, are broken into much finer flakes and frag- 
ments than in the original schisty stage. These changes are often local, and 
may or may not continue over any considerable longitudinal extent. Such 
is the variation of the material of the original beds, that while this breaking 
up of parallelism may occur throughout one bed, the enclosing strata may 
experience much less interior disturbance. The argillaceous and the more 
purely quartzitic beds suffer far less of this species of alteration than micé 
or hornblende beds. The observer is never at a loss to trace the planes of 
original bedding through these regions of molecular change. 

One of the most interesting places for observing this phenomenon is on 
the great gneiss precipices forming the eastern front of the range under 
Mount Bonpland. As the probable result of a great fault, and partly also 
from the abrupt carvings of the glacial névés, fine precipices, 1,500 to 1,800 


feet in height, are here exposed. As the gneiss beds dip to the west at an 


68 SYSTEMATIC GEOLOGY. 


angle of 15° to 25°, the whole wall is formed of their abruptly cut edges, 
which are traced in nearly horizontal lines, striping the front of the preci- 
pice. So well defined are the original beds by the predominance of mica 
or hornblende, or by the more purely quartzitic nature of some zones, 
that there is never any difficulty in following a given horizon over long 
distances. At the same time, the whole series is seen to be clouded in 
peculiar irregular shadings across the stratification, like an irregular map 
in different shades of gray. These clouded portions are found to owe their 
peculiar shade to the greater or less interior disturbance in the mineral 
particles of the strata. Following the nearly level edges of the series for 
several miles, they are observed to form gentle up-and-down curves, and 
always within the concave side of a curve, as would be readily inferred, 
there is a maximum of interior disturbance of the minerals of a given bed. 
Simple uniform parallelism was unmistakably the original attitude of all 
micas. ‘The hornblendes and feldspars lie with their longer prismatic axes 
in the plane of bedding, and the breaking up of this stage by local longi- 
tudinal compression has resulted in more or less comminution of individual 
crystals, besides crowding the fragments into utter disorder. 

Parallel, vertical, longitudinal fissures, trending with this part of the 
range, are developed along the summit near Clover Peak and Mount Bon- 
pland, apparently a series subordinate to and parallel with the great fault 
which has produced the eastern wall by dropping the eastern half of the 
range out of view. Erosion has taken advantage of these clefts and fissures 
in the rock, to produce a remarkable series of pinnacles 50 or 60 feet high, 
upon some of which are large, rounded, mushroom-like tops formed of beds 
which have successfully resisted the weathering. 

Near the summit within the gneiss series, and at one or two horizons 
far below, the microscope reveals, as an occasional constituent of the rock, 
crystals of calcite; in some instances there are enough of these to cause 
it to effervesce under acids. There is usually associated with the calcite 
a predominating quantity of triclinic feldspar, also rich in lime. At the 
extreme summit of the gneiss there are several beds of thin, brittle, saccha- 
roidal quartzite, among which are intercalated apparently very similar 
beds of highly compact dolomitic limestone of microcrystalline texture. 


ARCHASAN EXPOSURES. 69 


The entire limestone series is here not over 50 or 60 feet in thickness, and 
the individual beds vary from half an inch to six feet. Intercalated with 
the dolomites. are gneiss porphyries nearly identical with similarly asso- 
ciated rocksin Kinsley District. The upper beds pass through transition- 
beds into the pure quartzite which always contains in its lowest members a 
little microscopical calcite. 

The quartzite series, probably about 2,000 feet thick, appears chiefly 
along the middle and lower altitudes of the western side of the range, and 
also overlies the gray gneisses of Clover Canon. It is very well developed 
along the upper waters of Boulder Creek. 

The Clover Caton quartzites are probably direct equivalents of 
the great quartzite formation of the western slope, but show some slight 
characteristic differences, not enough, however, to render a correlation 
improbable. They are either white or stained a light yellow-brown by 
infiltrated oxyd of iron. Quartz, which is both milky and translucent, 
forms the mass. Under the microscope it shows no trace of the original 
grains of quartz sediment, but is a confused crystalline aggregate. Gar- 
nets, from the size of a pea down to fine microscopical grains, occur in the 
lower sheets of the Clover Canon quartzite, together with numerous flakes 
of white muscovite, which in general are disposed parallel to the bedding 
of the quartzite. The microscope also reveals fine black plates of horn- 
blende and minute prisms of actinolite, more or less dislocated The 
Clover quartzites are distinctly fissile, and split with very smooth faces, 
upon which are seen a multitude of striations indicating longitudinal motion. 
The surface of these divisional planes is more or less discolored with iron 
oxyd and spangled with plates of muscovite. Occasionally, rare and minute 

_erystals of feldspar rest on these smooth brown bed-faces. This appear- 
ance of striation is in no way due to the parallel arrangement of the mica, 
but is evidently the result of a true friction owing to longitudinal motion ; 
for the strize are traced on the strata surfaces in a variety of directions, indi- 
cating uneven, irregular, and evidently successive creeping motions. Al- 
though developed at intervals throughout the whole quartzitic series, these 
longitudinal movements have been very irregular, and there are consider- 


able areas which present no evidence of their existence. Observing these 


70 SYSTEMATIC GEOLOGY. 


marks of motion within the quartzites and gneisses, one is irresistibly led to 
believe that they are contemporaneous and the result of the same forces ; 
that the effect upon the quartzite is great compression and interior shearing 
parallel to bedding, while in the gneisses the result is a crumpling within 
the limits of certain beds, breaking the continuity of the sheets of mica 
plates, comminution of crystals, and the production of a granitoid rock. 

Along the western base of the range, in the vicinity of Thompson’s 
Ranch, the quartzites are duller than those of Clover Canon and grayer in 
hue, and though they are still characterized by the presence of muscovite, 
they carry also a little brilliantly black biotite. Evidence of motion is again 
observed upon the cleavage-surfaces, and here the mica itself is conspicu- 
ously striated. Plate III. shows a ridge of the quartzites east of Thomp- 
son’s and near the range summit. Higher on the ridge, above Thompson’s, 
there is an interesting case of diagonal cleavage, due to the restricted dis- 
turbance of a local fold in the quartzite. Here the muscovites are all diag- 
onal to the induced cleavage, but parallel to the original bedding, the brittle 
character of the material preventing a rearrangement of micas parallel to 
the newly produced cleavage-planes. ‘Toward the base of the quartzite 
series the mica is in some instances replaced by chlorite; and where, as is 
often the case, this mineral reaches a considerable importance in the rock, it 
may be properly called a chloritie quartzite. A few straggling garnets are 
observed in the low members of the quartzite, near the horizon of the dolo- 
mitic limestones. 

In the rocks here described the reader will have observed a certain 
general family likeness to those in the main mass of the Wahsatch, in the 
Farmington region. The association of various mica gneisses and horn- 
blendic, even dioritic schists, succeeded conformably by quartzites, marks 
an approximate identity of conditions with the Wahsatch and with Medicine 
Bow Range. The essential minerals of the range are quartz, orthoclase and 
plagioclase, biotite, muscovite, chlorite, calcite, dolomite, and hornblende, 
while the accessory minerals are garnet, zircon, actinolite, phlogopite, titanic 
iron, and apatite. 

Cortez Rance.—Among the many isolated mountain blocks which 
corrugate the surface of Nevada, few have greater geological interest than 


of 


ARCHASAN EXPOSURES. 7A 


Cortez Range. At Granite Canon, directly northwest of Cortez Peak, one of 
the higher summits of the ridge, a little north of the parallel 40° 15’, appears 
on the western flanks of the range a solitary mass of granite, surrounded 
by Tertiary voleanic rocks, which on the north are immense outpourings of 
buff rhyolite, and on the south high hills of quartz-propylite, culminating 
in Cortez Peak. Southwest it comes in contact, for a limited distance, with 
the upturned quartzites which have been referred to the Weber group of the 
Carboniferous, and on the extreme west its spurs are overlaid by an out- 
burst of diorite, which comes up in a synclinal of Carboniferous rocks. ‘The 
longer axis of the granite exposure is with the trend of the range, northeast, 
and is about five miles long, with an extent of three miles in the opposite 
direction, making a rude parallelogram, with a sharp point invading the 
rhyolites. The main mass is a single high spur boldly rising from the 
Quaternary of Crescent Valley in abrupt slopes of about 4,000 feet. It is 
a rude pyramid lying between two sharp lateral cations of the range. This 
granite possesses singularly few divisional lines. It is a remarkably solid 
mass of a pale cream-color, with shadings of gray and a faint pink. No- 
where else along the Fortieth Parallel is there an example of such extreme 
solidity with the absence of all planes of bedding or traces of conoidal 
structure. It is evidently of eruptive origin, and although no clew to its 
age beyond the unconformable superposition of the Carboniferous con- 
glomerates was observed, for reasons to be educed later in the chapter, it is 
conceived to be Archean. It is composed of salmon-colored orthoclase, 
frequently in broad crystals, slender white prisms of triclinic feldspar, appar- 
ently albite, quartz which appears both translucent and of a milky white- 
ness, long slim prisms of dark-green hornblende, and considerable biotite. 
Passages of granite which do not seem to be actual veins develop a coarse 
pegmatite in which the orthoclases reach two inches in length and the 
masses of quartz an inch. The pegmatite passages are of quite frequent 
occurrence, but they bear no apparent structural relations to one another. 
They cloud through the rock in various directions, and shade by perceptible 
eradations into the ordinary fine-grained variety. Hornblendes here eather 
in confused aggregations of needles. Besides the biotite, there also occurs 


an orthorhombic mica, doubtless muscovite. Under the microscope the 


72 SYSTEMATIC GEOLOGY. 


quartz is seen to contain many fluid inclusions. The rock also shows 
under the microscope a little magnetic iron and some apatite. 

South of this body, and obscurely occurring within the diorites of 
Agate Camon, is an insignificant outcrop closely resembling the granite of 
the Sierra Nevada, and composed of quartz, orthoclase, plagioclase, biotite, 
a brilliant black hornblende, which is peculiarly cleavable, and macro- 
scopical titanite. Owing to a considerable alteration in the feldspars, 
although both are clearly present, it is difficult to decide as to the predomi- 
nance of plagioclase or orthoclase. Of this decay of feldspar Zirkel says: 
‘The product of this decomposition is rather curious. It consists of broader 
or narrower prismatic, colorless rays, which, either orderless or confused, 
cross each other like a felt or are heaped together in forms of stars and 
bunches, presenting beautiful aggregate polarization.” This little mass is 
entirely surrounded by diorites, and may be a granite dike subsequent to 
the dioritic outflow. Although classed by Zirkel as a granite, it seems to 
me quite possible to consider it as an unusually quartzose passage of dio- 
rite, since nearly all the diorites of the Fortieth Parallel contain, besides 
the prevalent hornblende and plagioclase, a little quartz, occasional mica, 
and a small proportion of orthoclase. It is only necessary to increase these 
to a very slight extent to reach the composition of a granite rich in plagio- 
clase and hornblende and poor in quartz and orthoclase. Frequently in 
the great granite fields of the Sierra Nevada are observed passages which 
are unquestionably mere dependencies, in which plagioclase and hornblende 
predominate over orthoclase and mica. In such instances the quartz is apt 
to run low, and the rock, although a true granite, possesses the mineral 
nature of the abnormally quartziferous and orthoclastic diorite. It seems 
quite proper, when this same combination is found closely related to a dio- 
ritic outburst, to consider it rather as a diorite than as a granite, and such 
the Agate Pass body may well be. But since it has passed under Zirkel’s 
microscope as granite it is here included with those bodies. 

South of Cluro Station, on the Central Pacific Railroad, is a group of hills 
standing out in Crescent Valley and separated from Cortez Range by a broad, 
shallow, pass. They are composed of a central body of granite invaded by 
syenites and overlaid on the west by a quartzite, which is referred, for the 


ARCHAAN EXPOSURES. 73 


sake of convenience, to the Weber. The granite body is about five miles 
long by a mile broad, with a second outcrop near the western end of the 
hills, where a little dome rises through the horizontal Pliocene strata. ‘The 
granite is essentially the same as that of Granite Canon, in Cortez Range, 
lately described. 

Near the southwestern terminus of Cortez Range stands a very high, 
bold peak, called by the Indians Tenabo, which signifies “lookout,” a point 
commanding a very extensive view of middle Nevada. The main body of 
the range here is composed of a mass of granite which rises from the Quater- 
nary plain of Crescent Valley, and extends to within 800 or 1,000 feet of 
the summit, where it is overlaid by a capping of somewhat crystalline lime- 
stone, which has been referred by Mr. Hague to the Upper Coal Measure 
series. The overlying lime strata which rest unconformably upon the 
granite extend down the southern slope of the peak for three or four miles, 
making an irregular oval body entirely surrounded by granite. It is one 
of those interesting relics left by erosicn which give a clew to the rela- 
tive topography of the modern and Archean uplifts, for to that age the 
Tenabo granite is referred. The pass between Crescent and Grass valleys, 
which at Shoshone Wells has only an elevation of 1,000 feet above the plain, 
is also formed of the granite, which in passing westward is seen to be overlaid 
by the rhyolites of the Railroad Peak group. At its northern limit the granite 
is again overlaid by the limestones of the north flank of the range, also sup- 
posed to belong to the Upper Carboniferous. Mill Creek and the lesser 
streams on the north flank of Mount Tenabo flow through ravines of con- 
siderable depth, which offer excellent exposures of the granite, here seen to 
be a very tough rock, difficult of fracture, and with little tendency to dis- 
integration. It varies very much in texture, from fine to medium grained, 
and from light to dark gray tones, the latter being due to the variability of 
the proportion of feldspar and mica. It is composed of rather small trans- 
lucent grains of quartz, both orthoclase and plagioclase, with dark, partially 
decomposed biotites. The rock near the western end of the exposure, in 
the vicinity of the Shoshone Wells, is of a rather lighter color than the 
main body of Mount Tenabo, but otherwise shows little difference. 
Between the forks of Upper Mill Creek, under the western slope of Tenabo, 


74 SYSTEMATIC GEOLOGY. 


a mass which comes to the surface as an intrusive body through the granite 
bears a close resemblance to the dioritoid granite of Agate Pass, already 
described. It is compact and fine-grained, breaking with difficulty under 
the hammer, and showing along its fracture a rough, uneven, angular sur- 
face, and has an almost eryptocrystalline groundmass, composed chiefly of 
quartz, plagioclase, and fibrous hornblende. Like the Agate Pass rock, 
however, it contains a considerable proportion of orthoclase and quartz 
and a little biotite. Titanite, which occurs in the Agate Pass rock, was 
not observed here. It seems rather to represent an intermediate link 
between the granite and the diorite, and, like some of the bodies already 
mentioned in the great granite fields of the Sierra Nevada, may be con- 
sidered a dioritoid dependence of granite, or simply a granite in which 
triclinic feldspar and hornblende are present in abnormal quantity; the 
diagnostic point in such bodies being their association. 

Wan-wean Movuntains.—Directly south of Cortez Range, and only 
separated from the foot-hills of Mount Tenabo by the low pass of Gor- 
don Cut, which connects Grass and Gordon valleys, is a narrow mountain 
group called the Wah-weah, of which only the northern eight or ten miles 
lie within our map. On the west side of this group, in latitude 40°, is 
exposed a small body of granite underlying quartzite. The granite extends 
about three miles in a north-and-south direction. 

SeeroyA Ranee.—North of Humboldt River, in longitude 116°, is an 
irregular range extending from six miles north of Carlin Station to the north- 
ern limits of the map, a distance of about 45 miles. At Nannie’s Peak, the 
summit of the range, near the head waters of Susan Creek, is a granite out- 
crop coming to the surface through limestones of the Lower Coal Measures 
and brought in contact with a body of peculiar rhyolite. The mass is made 
up of a series of rude beds, having a strike from north to northwest and a 
dip of 65° westward, in conformity with the overlying limestone beds, 
which upon the west and south flanks of the body are wrapped closely around 
the granite. The bedding-planes of the granite are distinct. The higher 
peaks of the range are formed of very thick projecting strata of a granite 
which has all the interior lithological character of the eruptive type. It is 
composed of quartz containing numerous fluid inclusions, some of which 


ARCHAAN EXPOSURES. 75 


bear salt cubes, distinctly striated plagioclase, which is quite undecomposed, 
rare apatites, and orthoclase, which slightly predominates over the other 
feldspar and is not infrequently quite decomposed, showing here and there 
a distinct zonal structure, resembling sanidins in the trachytic family. 
Parts of the rock consist of a fine-grained accumulation of small crystal- 
line particles of quartz and feldspar like the groundmass of a felsite por- 
phyry. One variety contains little particles of hornblende, which seem to 
have been formed at the expense of the mica. Both of these granites are 
entirely free from titanite. That on the eastern slope of the range has a 
tendency to split into thin slabs, probably from contact with a curious rhyo- 
lite which once overflowed it and is now found farther down on the spurs. 
At the southern end of the high peak, in contact with the granite, appears 
a small body of true granitic porphyry. Farther south, at Maggie Peak, a 
long, narrow mass of granite porphyry protrudes through the overlying 
rhyolite, extending six miles in a north-and-south direction, being two 
miles broad at Maggie Peak. It seems to be an original Archzean summit, 
lifted above the limits of the rhyolite overflow. The groundmass consists 
of a fine mixture of quartz and feldspar, in which the crystallization is un- 
usually good. It contains infrequent clear granules of quartz, which Zirkel 
found, under the microscope, to be full of liquid inclusions, some of which 
contain salt cubes, both orthoclase and plagioclase, and an abundance of 
mica crystals. Apatite, very rare in corresponding German rocks, attains 
here a remarkable sharpness of crystallization. Green hornblende is occa- 
sionally found as an accessory mineral. At Maggie Peak itself is a light- 
gray variety, consisting very largely of a compact, homogeneous ground- 
mass, containing a very few large feldspar crystals. It is a rock which 
macroscopically bears a close resemblance to rhyolite, but under the micro- 
scope the felsitic groundmass has the same structure as the other porphyries, 
and its quartzes are full of fluid inclusions. 

ToyaBe Rance.—In latitude 39° 30’, longitude 117°, in the neighbor- 
hood of the town of Austin, near the western base of Toyabe Range, is a 
limited body of granite, upon which rest limestones and slates referred to the 
Carboniferous period, and which is partly environed by flows of rhyolite that 


evidently at one time entirely submerged the granite, but was eroded off at 


c 


76 SYSTEMATIC GEOLOGY. 


a later period, leaving traces of its former presence in a peculiar reddened 
and decomposed condition of the granite surfaces. This decayed condition 
of the surface is well shown on the divide above Austin. The undecom- 
posed, normal granite is an even-grained gray variety, consisting of quartz, 
slightly flesh-colored monoclinic feldspars, and pale-greenish plagioclase in 
about equal proportion, both very well crystallized, dark-green brilliant 
hornblende, black biotite in sharply defined hexagonal plates, the last two 
minerals in about equal proportion, and a plentiful development of titanite, 
the crystals of which are sometimes one eighth of an inch long. The mass 
presents no evidence of bedding; on the contrary, it is altogether structure- 
less, with the exception of innumerable faulting-planes, accompanied by 
veins of metaliferous quartz and granite dikes. The divide above Austin 
approaches more nearly to the source of the rhyolitic overflow, and is here 
penetrated by innumerable fissure-planes. Chemical decomposition has 
gone on to a great extent, resulting in the complete kaolinization of the feld- 
spars, which, however, still retain their crystalline outlines. Hornblende, 
mica, and titanite have disappeared, leaving amorphous earthy spots. The 
quartz alone seems to have resisted decomposition. It remains unchanged, 
except by the development of innumerable cracks and the occasional infil- 
tration of cloudy kaolinic matter. 

Rare as caustic contact phenomena are, the commonest examples in 
western America are where granite has been overflowed by volcanic rocks, 
and the characteristic features in such cases are the development of innumer- 
able vertical fissures and general infiltration of hydrous sesquioxyds of iron 
and manganese. In the Fortieth Parallel area there are no such extensive 
exhibitions as may be seen on the upper Stanislaus River in California. 

Directly east of Austin, in the Park Mountains, occurs a similar 
granite, in which the two feldspars are distinctly marked. Hornblende 
decidedly predominates over the mica, titanite being absent. Here, also, 
to a certain extent, decomposition has taken place. Passages are exposed 
in which the feldspars can be no longer distinguished, and the hornblendes 
appear in light-green, partly decomposed fibres, the mica having almost 
entirely disappeared. While the interior decomposition of the granite is 
evidently due to deep-seated causes, such as the penetration of acid vapors 


ARCHASAN EXPOSURES. V7 


and waters through the innumerable cracks and fissures, the peculiar super- 
ficial crumbling and peroxidation of the iron minerals is doubtless due to the 
effect of suddenly overpoured molten rhyolites. 

Suosnone Ranex.—The meridian of 116° 45’ passes through an 
exposure of granite lying about six miles east of Shoshone Peak. It 
is a rudely oval body, with the longer axis extended about four miles 
in the direction of the meridian, and with an east-and-west extent of 
about three miles. Along the south it is overflowed by a great body 
of rhyolites which skirts the east base of Shoshone Range for many 
miles. Otherwise it is surrounded by upturned quartzitic strata, which 
have been referred to the Weber group of the Coal Measures. The 
relation with the uptilted strata is somewhat obscure; indeed, it seems 
to be one of the most difficult geological problems afforded by this region, 
to decide, in a locality where confusedly tilted strata come in contact with 
eruptive granites, whether the latter have protruded through the strata 
in a plastic state, or have been thrust up as an underlying solid point. The 
configuration of the granite topography of the Archzan surface prior to 
the deposition of the Paleozoic series, was that of an area of mountain 
ranges, possessing some very abrupt precipitous walls, sharp, lofty peaks, 
and broad, low domes. Where these came to be uptilted together with 
superjacent strata, and afterward exhumed by erosion, which brought to 
light granite peaks piercing through highly inclined beds, it often becomes 
absolutely impossible to determine the relation of the two. In the absence 
of any granitic dikes penetrating the stratified series, or of peculiar local 
metamorphism, or of general evidence of intrusion, the bodies are 
usually referred to the old Archzean topography. Only in cases where the 
granite is actually seen to penetrate either fissures or warped openings in 
the strata, is it safe to refer it to a later origin than the sedimentary series. 
This question, as applied to the majority of the granite exposures of Nevada, 
will be more thoroughly discussed later in the chapter. 

Structurally the Shoshone granite develops in interesting perfection 
the broad conoidal bedding after the type of the Sierra Nevada domes. 
The rock is composed of predominant quartz; orthoclase and plagio- 
clase in almost equal proportion, biotite, a great deal of easily cleav- 


78 SYSTEMATIC GEOLOGY. 


able black hornblende, and a little microscopic apatite. For uniformly 
mixed granite there is an unusual discrepancy in the size of the quartz and 
orthoclase particles. Quartz masses from half to three fourths of an inch 
in diameter are observed, carrying many enclosed plates of biotite and 
fluid inclusions. Excellent hexagonal biotite crystals were observed, whose 
faces are covered with an interesting iridescent tarnish. The color of the 
plagioclase is a clear white, and it appears in stout crystals resembling 
albite. The orthoclase shades from white to rusty yellow, owing to micro- 
scopic infiltrations of iron oxyd. 

The cation of Reese River severs Shoshone Range into two well 
marked divisions. The southern portion is a single broad flood of rhyolite, 
from which, at a few localities, rise isolated outcrops of older rocks. At 
Ravenswood Peak, certain of the Carboniferous beds, an intrusion of diorite, 
and small exposures of granite and granite porphyry occur. For eight miles 
south of that point, the summit is formed of one of these outcropping 
islands of older rock lifted above the slopes of the rhyolite. It is a 
narrow meridional mass of granite, about eight miles long and from one to 
three miles wide, flanked upon either side by narrow zones of steeply dipping 
schists. This stratified series dips east and west away from the central 
granite mass, which has rather the appearance of an intrusive core. From 
their likeness to other known Archean rocks, and for the want of reasons 
to the contrary, these schists, together with the granite, are referred to the 
Archean. Parallel divisional planes standing at a very high angle occur 
with considerable regularity in the granite, giving it almost an appearance 
of stratification. As the identical granite penetrates the schists in the form 
of a dike, there seems no doubt that the whole mass is of eruptive origin. 


It consists of quartz, orthoclase, a few scattered grains which appear to be 


minute crystals of plagioclase, and white orthorhombic mica—probably 
muscovite; but there is no hornblende, black mica, or titanite, and very 
little apatite. The dike which invades the schists is made up of a similar 
but coarser-grained material, in which there are clearly two feldspars (the 
predominating one a white or pale salmon-colored, smoothly cleaving ortho- 
clase) and a few minute prisms of triclinie feldspar, large accumulations of 


grains of smoky quartz, and irregular bunches of muscovite. 


ARCHASAN EXPOSURES. 79 


There is something unusual and suggestive in the superior coarseness 
of the mineral components of the dike. Ordinarily, over the area of this 
Exploration, dike minerals have far greater fineness than those in the parent 
irruptive mass, due not unfrequently to friction and comminution during 
intrusion. Perhaps the state of things here is explained by supposing that 
within the walled and protected dike there was less opportunity for the 
intercrystalline attrition due to orographical movement than in the larger 
and more exposed body. 

The accompanying schists are of two types. One is a very fine-grained 
compact rock, whose broken faces display a very steely crystalline shim- 
mer, as from extremely small facets. Yet even the loupe does not discover 
any crystalline ingredients, the general appearance being that of a fine- 
grained anamesite; the microscope, however, develops an aggregation of 
very minute particles of quartz and two micas, biotite and muscovite. 
Besides these, on the western flank are found series of fine mica schists 
having the same composition as the more compact rock, except that the 
constituent particles are larger, and that parallel sheets of minute mica 
plates produce a bright, irregular reflection of light from the whole sur- 
face. They may be called spotted mica schists, and are not unlike those 
described in the neighborhood of the Irish granites by Haughton. ‘These 
spots, which the microscope made out to be densely compacted grains of 
mica, are not thick enough to give it the name of ‘“Mnotenschiefer.” It 
seems probable that the spots represent the features of local metamorphism 
after the manner described by J. Clifton Ward in his article on the granitic, 
granitoid, and associated metamorphic rocks of the lake district.* These 
spotted schists are closely allied to the rocks of the Wright's Canon mass 
in West Humboldt Range, the main difference being that here the con- 
stituent particles are finer, and there are interesting bronze passages of 
schist whose color is derived from infiltrated oxyd of iron. 

Aveusta Mountaiys.—On the eastern side of the Augusta Mountains, 
near the northern end of Edward’s Creek Valley, is exposed a small body 


of granite about two miles in extent, overflowed and surrounded on the 
north and west by rhyolite, which here forms the dominant rock of the 


* Part III., Quarterly Journal of the Geological Society, Vol. XXXII, page 1. 


80 SYSTEMATIC GEOLOGY. 


range, and separated from the Quaternary of the valley by a belt of sedi- 
mentary rocks of Alpine Trias age. Save that the Trias reposes uncon- 
formably upon it, there is no clew to the age of this granite. Lithologically 
it belongs with the older eruptive granites, and is composed of grains of 
varying size of pellucid or slightly smoky quartz, a very large amount of 
somewhat earthy orthoclase, considerable biotite, a small but varying propor- 
tion of hornblende, and a very little apatite. Some specimens show the 
orthoclase of a pale olive-green color, and peculiar strings of crumpled, 
decomposed mica. The biotite shows an unusual facility for decomposition, 
so that the exposed and weathered faces of the rock exhibit numerous hex- 
agonal pits, out of which the products of decomposition have been washed. 

Fiso Creek Mountains.—Fish Creek Mountains, the northern exten- 
sion of the Augusta group, are almost entirely formed of rhyolite. - Along 
the western slope of the northern extremity of the range are a few limited 
basaltic outflows, and the extreme western base, to the west of Mount 
Moses, shows a narrow band of granite extending along the foot-hills for 
about four miles north-and-south, by less than a mile in width. It is overlaid 
unconformably by Triassic strata. It is a dense, compact rock, composed 
of quartz, orthoclase, and biotite, with a little plagioclase, and is destitute of 
structural indications of a metamorphic origin. It is doubtless to be classed 
with granites in the regions lying to the northwest, which represent a 
general Archean highland over which the Triassic beds are laid down. 
Together with the limited exposure at Granite Point, where it is again over- 
laid by Triassic strata, these granitic foot-hills near Mount Moses represent 
a portion of an Archzean body which may be largely developed immedi- 
ately beneath the immense flood of rhyolite now covering the surface of this 
early range. 

Havautian Rancr.—A little north of latitude 40° 30’ Havallah Range, 
in passing northward, bifurcates like a rude letter Y, the most eastern arm 
trending off about 25 miles in a northeasterly direction, and sinking below 
the Quaternary plains in the region of Stone House Station. The upper 
fifteen miles of this arm are composed of a lofty mass of granite, which 
rises abruptly to its culminating points nearly 4,000 feet above the plain. 
On its southern edge, at Summit Springs Pass, the granite is overlaid by 


ARCHAAN EXPOSURES. 81 


Alpine Trias strata. The plain of Ragan’s Valley on the west has an alti- 
tude of 4,500 feet, the highest summit of the granite body reaching 8,150. 
The topography is decidedly rugged, and it is more minutely varied than the 
usual exposures of Archeean rocks in Nevada. It is all but certain that 
even during the deposition of the Trias and the conformable Jura, parts of 
this range were lifted above the limits of deposition and suffered erosion 
from a very early period. The broken and serrated outline which char- 
acterizes the summit of this group renders it essentially different from the 
neighboring granites. Although not possessed of any distinct planes of bed- 
ding, this occurrence, in many of its physical aspects, recalls the metamorphic 
granite bodies described in Colorado Range. It is coarse-grained, ill-com- 
pacted, and readily disintegrates, leaving irregular-shaped fragments. There 
seems to be far less uniformity of texture than is usually the case in eruptive 
granites. The prevailing color is a dull gray. The essential constituents are 
quartz, orthoclase, plagioclase in brilliant but small crystals, bearing wonder- 
fully fresh striae, small dark plates of biotite, more or less decomposed, and 
a little hornblende in small, dark-green crystals. The orthoclase occurs in 
crystals of various sizes, some of them reaching three inches in length and 
having broad tabular faces with brilliant lustre. They are usually a bluish, 
smoky gray, near the ordinary hue of labradorite. Infiltrations of oxyd of 
iron have penetrated the rock in every direction, leaving a thin ocherous 
coating on many of the broad faces of the feldspars. Under the microscope 
Zirkel discovers many points of interest in this rock. Apatite, magnetic iron, 
and muscovite seem to be accessory minerals. The reader is especially re- 
ferred to Zirkel’s memoir for a description of the inclusions of the feldspar. 
He describes the quartz granules as containing three forms of liquid inclu- 
sions. simple water-bubbles, liquid carbonic acid, and compound bubbles 
containing both water and carbonic acid. 

On the east side of the range, a little north of Summit Springs, the 
main body of granite is penetrated by a narrow dike which has clearly the 
properties of an intrusive body and bears a close resemblance to the granites 
of the Sierra Nevada type. The association of intrusive granite bodies 
with the older forms of Archzean granite is decidedly exceptional over the 
area of the TFortieth Parallel. In Colorado Range there are indeed some 

6 Kk 


82 SYSTEMATIC GEOLOGY. 


instances of bold intrusive masses penetrating the essentially metamorphic 
granites, and in the case of Mount Clayton and the Little Cottonwood mass, 
in Wahsatch Range, there is probably a repetition of this association; but 
it is extremely rare in the country west of the Wahsatch. The granite dike 
north and east of Summit Springs is a comparatively fine-grained rock, 
breaking with difficulty under the hammer, and leaving an uneven, angular 
surface. The constituent minerals have a fresh, unaltered appearance, and 
in color the rock is of a brilliant gray, of which the irruptive Californian rock 
may be considered a type. It is composed of quartz, orthoclase, brilliant, 
pearly plagioclase, biotite, and hornblende, and the microscope detects a 
very minute proportion of hair-brown titanite. Hornblende and plagioclase 
rise to considerable importance as principal constituents, almost to the point 
of shading the rock into those questionable bodies which appear to lie be- 
tween granite and diorite. Indeed, we have only to increase these constit- 
uents a little to produce the dioritoid rock of Cortez Range. Biotite is in 
the form of brilliant, symmetrical, black hexagons. The hornblende is very 
dark green, and has an extremely fibrous structure, suggestive of the horn- 
blende belonging to the propylite family. The quartz contains a few salt- 
bearing fluid inclusions. 

Dikes of fine-grained diorite, composed of dark-green hornblende and 
triclinic feldspars, oceur within a few miles of Summit Springs. 

On the northwest side of Ragan’s Valley, opposite the above-described 
granite body, is another exposure of the same sort. It is only about ten 
miles from north to south and four miles east-and-west. As the map indicates, 
it is partly overlaid by strata of the Alpine Trias period, the east base 
being wholly bordered by the Quaternary plain of Ragan’s Valley. On the 
west it is about equally bounded by Quaternary of Rocky Creek, rhyolites 
which extend southward from Golconda Station, and Alpine Trias of the 


main Havallah R 


ange. Though of much lower and less conspicuous topo- 
graphical configuration than the body to the south, this second mass is, by 
its petrological nature, closely related to the Summit Springs body, and 
may be considered as the northern extension of it, merely separated from 
the main mass by a shallow covering of Quaternary. It is, perhaps, a little 


less loosely compacted, and is distinguished from the other body by distinet 


ARCHASAN EXPOSURES. 83 


bedding-planes, which have a rather gentle dip toward the west. Near its 
southern extremity, directly north of Cold Run Creek, the granite is pene- 
trated by a dike between 20 and 30 feet in width, which stands nearly 
vertical, striking with the trend of the Havallah. It is a dense, dark-gray 
rock of high specific gravity, with a fine microcrystalline groundmass, in 
which crystals of hornblende and occasional segregated groups of mica 
plates are porphyritically inclosed. Essentially made up of quartz and horn- 
blende, it is probably another of those singular dioritoid dependencies of 
granite which are often seen connected with large bodies of that rock. 

A third granite locality within Havallah Range is exposed upon its 
west base, between the mouths of Clear Creek Canon and Bardmass’ Pass. 
Here a strip of granite, nowhere over a mile wide, extends along the extreme 
foot-hills of the range, sloping under the Quaternary of Grass Valley and 
flanked upon the east by beds of the Alpine Trias series. Topographically 
it consists of the points of three main spurs of the range, weathered into 
rounded and conical hills. As usual, where forms are at all pointed, the 
granite is of a hard, compact texture and resists weathering most deter- 
minedly. It is of a dark, warm gray tint, and consists of quartz, orthoclase, 
brilliant striated plagioclase, a little dark-green hornblende, and a very little 
mica. In general, it may be characterized as of eruptive habit. 

Pan-Ute Rance—Pah-Ute Range traverses Map V. from north to 
south with a remarkably sinuous trend, consisting mainly of a broad con- 
vex curve thrown to the east, with minor convexities at each end turned 
westward. It consists essentially of Archzean rocks, granites, and granitoid 
gneisses, overlaid by the immense conformable series of Trias, Alpine Trias, 
and Jura; and these in turn are overlaid and deluged at different points by 
Tertiary volcanic rocks. The granitoid masses in the neighborhood of 
Tarogqua Peak, in the southern part of the range, have been but little 
studied. The mass of Granite Mountain is in every way the most im- 
portant Archean body of our part of the range, and in consequence has 
received much closer study than the other. 

Granite Mountain mass is an oval body, touched by the parallel of 40° 
15’, having its longer axis of about twelve miles extended in an east-and- 


west direction, with a shorter diameter of about eight miles. This expo- 


84 SYSTEMATIC GEOLOGY. 


sure is wholly composed of granitoid rocks having a distinct east-and-west 


strike and standing at very high angles—indeed, approaching the vertical. 


It is interesting to observe that, while these Archean strikes are altogether 
in a direction approximating to the east-and-west line, the later sedimentary 
rocks of the range are all nearly in a north-and-south position. This 
Archean strike makes itself particularly felt in the lesser topographical 
structure of the body. As may be seen by a glance at the map, the 
leading streams near the contact of the granite body with the quartzites to 
the north have nearly easterly directions. The granitoid rocks which con- 
stitute this exposure are made up of quartz, orthoclase, and plagioclase, 
with minute, unimportant additions of mica and hornblende. In short, it 
is essentially the same aplitic compound as that already described in Colo- 
rado Range. They are distinctly bedded, but without any observed paral- 
lelism in the arrangement of the individual minerals. The rock is a light, 
flesh-colored mass, generally medium grained, and is more or less clouded 
with stains of infiltrated iron oxyd. Decomposition has gone on to a cer- 
tain extent in the orthoclase and mica, but the triclinic feldspars, which 
are probably oligoclase, have retained their original freshness and brilliance. 
The dark biotite is gathered into minute segregations of broken flakes, and 
it seems to be far more prevalent in some east-and-west zones than in 
others. Under the microscope, Zirkel detected liquid carbonie acid in 
the quartz. Black tourmaline occurs in veins of granite east of the geodetic 
station on the summit of Granite Mountain; also brown iron garnets asso- 
ciated with light mica. On the ridge east of the summit of Granite Moun- 
tain is a narrow band of feldspar porphyry, having an east-and-west strike 
and lying conformably with the granite zones. It consists of a microgra- 
nitic groundmass of a brilliant grayish-white, stained here and there by oxyd 
of iron, and carrying brilliant crystals of feldspar and irregular granules of 
pellucid quartz. It seems to be referable to the same origin as the granite 
itself, and is to be classed with the granitoid porphyries of Kinsley Dis- 
trict and Franklin Buttes. It is an exceptionally fine-grained zone of met- 
amorphie granite, not an intrusive dike. 

About fifteen miles to the north, along the east side of the range, is 
another important exposure of granite. At Granite Mountain the Triassic 


ARCHAAN EXPOSURES. 85 


beds are flexed around the eastern end of the granite mass, but here they 
bend around the western side, the whole line thus describing a sort of 
sigmoid curve about the two granite centres. The topography of the 
Spaulding’s Pass mass is that of lofty conical hills and high rugged spurs, 
the slopes of which descend to the level of Grass Valley. It is a hard, 
compact, medium-grained, light-red granite, without the evidences of bed- 
ding or the variability of zones seen at Granite Mountain. It is probably 
an eruptive rock, related to the small body at the western base of Havallah 
Range, directly across Grass Valley. 

West Humsoipt Rance.—On the west side of West Humboldt 
Range, about six miles north of Sacramento Canon, is exposed in the 
body of the range a mass of granite and accompanying crystalline schists. 
They are well seen in Wright’s Canon and in the two canons next north. 
The whole exposure is in the form of a broad oval, about four miles in its 
longer direction of northwest-and-southeast. The southern two thirds are 
of true eruptive granite, the remainder a variety of crystalline schists. This 
body is evidently an old Archzean summit, over which the quartzites, argil- 
lites, and limestone beds of the Alpine Trias were deposited. At the post- 
Jurassic period of folding of this range the Archean mass was somewhat 
driven through the strata and slightly shoved to the west, throwing the strata. 
into sharp curves, the Alpine Trias limestones and quartzites wrapping 
completely around the north and west sides of the body. In the region 
of Wright’s Cafion the granite is more or less intersected by jointing- 
planes, which strike mainly northeast or northwest, standing nearly vertical. 
At the top of the canon are developed certain broad conoidal bodies, not 
unlike those of Shoshone Knob, by no means comparable with the Sierra 
Nevada domes, but still suggesting the true conoidal habit. These two 
localities and the so-called City of Rocks in Southeast Idaho offer ex- 
amples of fairly regular cones, which on the whole seem to be the result 
of a kind of weathering due to a soft and rather decayed exterior. There 
are none of the characteristic conoidal shells which are developed in so 
symmetrical a mode throughout the domes of, for instance, the Merced 
region in the Sierra Nevada. The rock is composed of a very coarse- 
grained association of colorless and dusky quartz, yellowish and white 


86 SYSTEMATIC GEOLOGY. 


orthoclase, either very little plagioclase or none at all, and two species of 
mica—a white muscovite chiefly included within the quartz masses, but now 
and then seattered in minute white spangles through the orthoclase, and a 
normal proportion of biotite, which is at times a good deal decomposed into 
a brownish-ereen fibrous condition, suggestive of the transition into chlorite. 
Black hornblende occurs, but it is segregated into bunches not well dis- 
seminated through the rock. Neither titanite nor apatite was observed. The 
contact of the granite with the associated family of schists is very inter- 
esting; it shows in horizontal plan an irregular, angular intrusion of 
granite into the schist, with outlying insular masses of schist wholly enclosed 
within the granite, or promontory-like masses jutting from the schist into 
the granite. One of these points extends 400 or 500 feet into the gran- 
itic mass. On the edges of these included bodies of schist, and indeed 
along the whole contact between granite and schist, there is no tendency 
toward a passage by gneissoid gradations between the two rocks; the line 
of demarkation is always sharp and clearly observable. In the vicinity 
of the schist the granite is penetrated by a great number of structural 
planes, having a strike partly with the bedding of the schists, as if the part- 
ings of that rock had somewhat controlled the lines of fissure. There is 
also another set of joints, with a direction of north 36° west, or approxi- 
mately at right angles to the schist. A few dikes of granulitic material, 
containing rare crystals of feldspar and a few raspberry-colored garnets, in- 
vade the schists. As a whole, the schists strike about north 50° east, and 
are either vertical or dip at a high angle to the northwest. 

The lower members of the altered sedimentary rocks are excessively 
fine-grained mica slates, carrying coarse limpid granules of quartz. It is 
a Knotenschiefer in which the nodules are aggregated heaps of mica flakes 
or nuclei of large grains of pellucid quartz, around which the flexible, 
matted mica scales are bent. The mica appears to be chiefly muscovite, 
although small flakes of a black variety, probably biotite, are present. 
An interesting peculiarity of this rock is the minute corrugation of the 
sheets of mica, which are flexed between the mica and quartz nodules. 
The whole surface of one of these sheets of felted mica is corrugated in 


the most minute wrinkles, of which fifty or sixty can be traced in an inch. 


ARCHASAN EXPOSURES. 87 


An irregular decomposition has taken place between the laminz of the 
rock, resulting in a bright, almost orange-colored oxyd of iron. The lower 
mica schists are dark silver-gray. Above these occurs a zone of creamy- 
white or yellow-stained mica schists, made up almost wholly of minute 
quartz grains and excessively small plates of muscovite, embedded in which, 
as in the last described lower series, are large grains of limpid quartz, 
sometimes one fourth of an inch in diameter, and disposed like pebbles in a 
conglomerate, the mica bending over and enclosing them. In this also the 
same minute, interesting corrugation bears witness to an internal compres- 
sion of the whole series. An association of excessively fine muscovite with 
such large angular fragments of quartz is not found elsewhere in the Forti- 
eth Parallel area. Passing up in the series, the muscovite gradually gives 
place to minute quartz grains, but it still contains a few of the large pellu- 
cid quartz fragments. Here again the internal corrugation is seen upon 
every fracture-surface, and the rock becomes a quartz schist. These quartz 
individuals are somewhat difficult to account for. At first glance they 
might be explained as the small pebbles of a conglomerate whose argilla- 
ceous matter had passed by metamorphism into muscovite. Such unaltered 
conglomerates are not unknown in the Rocky Mountain Cretaceous—rocks 
in which small pebbles are thickly interspersed without the ordinary ar- 
rangement parallel to the stratification. Another, and doubtless a sounder 
hypothesis, is the aggregation during metamorphosis of like particles with 
like, as is seen in the Archzean gneisses of Humboldt Range, where groups 
of orthoclase form in the midst of a felt of rusty biotite. 

Montezuma Rance.—In the Montezuma Hills, Archean rocks play : 
very important role. The range is topographically divided into several 
groups, separated from each other by considerable depressions and distin- 
guished by great geological variety. A prominent depression in the region 
of latitude 40° 30’ severs the range and permits the beds of the Miocene 
Tertiary to stretch through from valley to valley. North of this pass the 
range rises to a high granitic summit in Antelope Peak, and dipping away 
from either flank of this are great masses of rocks which have been referred 
to the Jurassic period. On the extreme northern and eastern edge it is in 
contact with the Quaternary beds of the Humboldt plain, and also with a 


88 SYSTEMATIC GEOLOGY. 


limited outflow of basalt which skirts its base. The body lying to the east 
of Antelope Peak is of rather less extent, though similar in position, being 
flanked on the west by the slates of the Jurassic series and on the east by 
the basalt and the Quaternary plain. About its southern point are wrapped 
the disturbed strata of the Truckee Miocene. 

South of the pass the range again rises to a lofty ridge characterized 
by quite complicated topographical forms. It is made up of a middle band of 
granite, accompanied upon either side by flanking belts of Archean schists. 
This composite body has an extent of twenty miles in the direction of its 
trend, by about twelve miles in extreme breadth. The isolated knob of 
granite rising out of the Humboldt plain west of Lovelock’s Station, called 
Lovelock’s Knob, may be regarded as a dependence of the main Montezuma 
granite. So also the several granite outcrops from which erosion has removed 
the general covering of basalt in the spur west of Granite Point are sub- 
ordinate parts of the larger block. For a distance of fifty miles, therefore, 
granite is a frequently recurring feature; and, together with the crystalline 
schists in the region of Trinity Cafion, it may be said to constitute the core 
of the range. South of Valley Canon the whole range consists, with but 
unimportant exceptions, of volcanic outflows which have overwhelmed and 
submerged all the older rocks. The slight exposures in the vicinity of 
Lovelock’s Knob and Granite Point are chiefly of a coarse, crumbling 
granite, very rich in orthoclase, and in rather large, irregular grains of 
pellucid quartz, together with a sparing quantity of more or less decom- 
posed biotite 

The most important Archean exposure is that which culminates in 
Trinity Peak. Here the granite belt, from twelve to fifteen miles long by 
four miles broad, occupies the higher portion of the range. It is deeply 
sculptured by erosion, and the sharp canons lay bare a depth of from 1,200 
to 1,500 feet of granite slopes. The general surface shows a great deal of 
the results of easy disintegration, in the form of granitic gravel which often 
masks the more solid portions of the rock. At the northern extremity of 
this body, west of Rye Patch Station, the rock is a uniform fine-grained 
mass composed of quartz, orthoclase, a little oligoclase, and plentiful mica 


and hornblende, the latter of a dark-green color and decidedly fibrous crys- 


ARCHASAN EXPOSURES. 89 


tallization. Biotite is present in well developed hexagonal plates, which 
are usually more or less decomposed and stained an earthy brown. 

Directly south of this body, and four or five miles northwest of Oreana, 
in the midst of a broad field of rhyolite, is an isolated hill of granite, which 
is of interest as forming the country-rock of the Montezuma Mine. Like 
the granite west of Rye Patch, it consists of quartz, both feldspars, horn- 
blende, and mica, but, if anything, it is rather more decomposed. It 
belongs to the decidedly basic granites, and although more siliceous than 
that of the Wachoe Mountains, approaches it in composition. This whole 
Trinity body of granite is undoubtedly of eruptive origin, as may be 
determined from its general habitus and from its penetrating the Archzean 
schists in well defined dikes. 

From this granite core the two bodies of Archzean schists dip in con- 
trary directions, forming a steep anticlinal. The eastern body, well shown 
in Trinity Canon, has a dip of 60° to the east; that on the west side 
of the range, directly west of Trinity Peak, dips from 50° to 60° to the 
west, with a well defined strike of about north 45° east. In these schist 
bodies there are 4,000 or 5,000 feet of conformable beds of a remarkably 
uniform appearance. Their color ranges from dark steel-gray to black, 
with a fine but brilliant lustre on the freshly fractured and cleaved faces. 
The naked eye is only able to detect a fine microcrystalline mass, but the 
microscope resolves the body into a compact admixture of quartz, biotite, 
muscovite, and magnetite. In all the specimens we obtained there is a 
total absence of both feldspars. Throughout the upper part of Trinity 
Canon the schists are penetrated in different directions by small granite 
dikes, petrologically allied to and doubtless depending upon the main, mid- 
dle mass of granite. 

The second large body of granite already indicated as lying east of 
Antelope Peak in that portion of the range north of Indian Pass, so far as 
our slight geological observations go, appears to be a petrological repeti- 
tion of the larger body. The two are of medium texture and of a variable 
light color, being made up of quartz, orthoclase, and large amounts of well 
developed brilliant hexagonal plates of biotite. It would seem, therefore, 
that the central body, which is associated with the Archaean schists, differs 


90 SYSTEMATIC GEOLOGY. 


from the other granites of the range in its considerable proportion of horn- 
blende, while that of Lovelock’s Knob and that of Granite Point seem to 
be more nearly uniform with the two northern bodies in the low percentage 
of hornblende and the presence of well developed hexagonal biotite. These 
bodies are referred to the Archean age simply on petrological evidence. 
This mode of correlation is dangerous, but a general study of the whole 
region has strengthened the belief that in the Paleozoic series as a 
whole there are none of those results of extreme metamorphism which in 
the Appalachian system are described by some geologists as closely approxi- 
mating to Archean forms. 

Pan-tson Mountarns.—From the Quaternary plain west of Indian Pass 
rises an isolated body of mountains extended about twenty miles a few degrees 
east of north, and having an extreme width of about eight miles in the middle 
of the body, near Pahkeah Peak, the highest point of the range. This summit 
rises about 3,300 or 3,400 feet above the desert plains at its base. The group 
consists essentially of a small mass of granite and Archzan schists, extend- 
ing from near the northern limits of the hills southward for ten miles along 
the west side of the range, rising toward the centre, and occupying the 
summit in the region of Pahkeah Peak. Eastward, the entire Archsean 
series is surrounded by outflows of Tertiary volcanic rocks, chiefly rhyolite 
and basalt. The Archzean nucleus itself consists of three distinct members: 
crystalline schists closely resembling those already described in Trinity 
Canon on Montezuma Range; a limited amount of granites; and a subse- 
quent granite which has broken through the older granite and schists, over- 
flowing them ina broad field to the north. All the crystalline schists occupy 
a region from the mouth of Crusoe Canon to the mouth of Frost Canon, 
with a breadth of about three miles, culminating in Pahkeah Peak. To the 
unaided eye they closely resemble the fine granular-crystalline condition of 
the Trinity Canon schists, but under the microscope Zirkel found them to 
be composed of quartz, biotite, and muscovite, with, in one instance, thin 
laminze of a third mica, having an oil-green color. As in the Montezuma 
schists, there is no trace of either feldspar, and no tendency either to a 
minute schistose arrangement of the beds or to interior parallelism between 


the constituent minerals. There is, however, a distinct broad bedding, 


ARCHAAN EXPOSURES. 91 


which defines a very high dip and a north-and-south strike. Associated 
with these is a further development of a fine-grained homogeneous rock, 
which, though possessing little outward resemblance to the quartz and mica 
rock, is nevertheless nearly related to it. It occurs near the head of Crusoe 
Canon, the high ridge southwest of Pahkeah Peak, and has the aspect and 
fracture of a quartzite, but the microscope shows it to consist of minute 
crystals of delicate green hornblende and quartz. Feldspars are again 
totally wanting. The rock appears to be exactly like the other schists, with 
the substitution of hornblende for mica. In contact with the schist body 
is a limited exposure of granite, whose original northward extension is 
wholly unknown, since it is overlaid by a more modern granite, to be 
described later. Near the head of Crusoe Canon this older granite appears 
with a surface characterized by great decomposition, resulting in rusty 
earthy débris, and even the more solid parts of the rock have an extremely 
friable texture. Quartz, orthoclase, and muscovite form the chief con- 
stituents. 

Both this granite and the accompanying schists are more or less inter- 
sected by dikes, likewise supposed to be of Archean age. One in particular 
is observed in Crusoe Canon, a very fine-grained, pearly-gray granite, in 
which are coarse passages of pegmatite, carrying the quartz both in broad 
irregular masses and fine-grained passages; orthoclase crystals, not infre- 
quently four inches long, and having the lustrous appearance of pure, unde- 
composed feldspar; muscovite, lepidolite in thin lamine, brilliant black 
erystals of tourmaline, and garnet intimately associated with colorless 
muscovite. Neither biotite nor hornblende is present. Other dikes trav- 
ersing the schists in the same region possess a very fine-grained association 
of the same minerals, the tourmaline especially rising to so high a percent- 
age as to carry the rock into the schérl granites. Whatever may have been 
the origin of this dike, whether distinctly eruptive, or, as seems to the 
writer far more probable, the result of hydrothermal secretion, it is an 
interesting fact that in its body are included noticeable masses of the crys- 
talline schists, which have either fallen in during the process of forma- 
tion or in some manner been involved while the rock was in a plastic con- 
dition. 


92 SYSTEMATIC GEOLOGY. 


‘Lying to the north of Pahkeah Peak is a stretch of granite extending 
for four or five miles, which apparently overlies and masks the older granites 
already described. It is a very fresh, clear, bright-grained stone, with none 
of the evidences of decomposition and ferric infiltration which characterize 
the underlying variety. Quartz, orthoclase, a high percentage of plagio- 
clase, mica and hornblende in variable quantities, and titanite enter into 
its composition. Under the microscope considerable apatite, specular iron, 
and occasional bodies of magnetic iron are seen. In the petrographical 
scale it comes near the basic limits of granite, having of silica 64.02, while 
there is twice as much soda as potash, which indicates either a predominance 
of plagioclase or that the orthoclase belongs to that group in which the pro- 
portion of soda rises to unusual prominence. 

North of the Pah-tson Mountains, and lying in the gap between Grass 
Canon and the Kamma group, are three isolated outcrops of granite coming 
to the surface through the Miocene beds. They are of no interest, except 
as indicating the northward continuance of the Pah-tson granite, which in 
the region of Grass Canon is undoubtedly buried beneath the Tertiary 
voleanic rocks. Finally, it may be said that the entire habitus of both 
species of granite is distinctly that of an eruptive product bearing no 
resemblance whatever to those we have classed as metamorphic. 

Paun-supp Mountarns.—West of the Pah-tson group, and entirely sur- 
rounded by broad fields of Quaternary, is a very irregularly shaped group, 
which has been called the Pah-supp Mountains. It consists of a prominent, 
bold ridge, extending in a well defined line along the eastern margin of 
the body, and a long, irregular slope to the west, invaded on the north 
and south by bay-like regions of Quaternary. The main sharp ridge, 
which has a trend of 15° or 16° east of north, attains an altitude of a little 
over 3,000 feet above the desert, and is flanked on the eastern foot-hills of 
its north and south extremities by narrow bands of highly inclined slates 
and ealeareous shales which have been referred to the Jurassic age. The 
main body of the range is of a uniform granite, not to be distinguished in its 
mode of occurrence and general features from the more recent of the granites 
of the Pah-tson. It consists of quartz, orthoclase, plagioclase, hornblende, 


and mica, and only differs from the other in the absence here of macro- 


ARCHAAN EXPOSURES. 93 


scopic titanite. Under the microscope Zirkel observed in the quartz a 
great number of fluid inclusions. The granite is frequently traversed by 
fine narrow seams of quartz and thin veins of fine-grained, massive feld- 
spar, varied by a few scattered grains of quartz. ‘Toward the north end of 
the group, opposite the Kamma Mountains, the granites are more compact 
and rather lighter colored, owing to the diminished proportion of mica and 
hornblende. The quartz, too, occurs in rather larger transparent grains. 
An isolated body of granite lies to the south of this group and establishes 
a geological connection between it and the Sahwave Mountains. The 
single specimen brought in from this knob distinctly identifies it with 
the Pah-supp hornblende-plagioclase-bearing granites. Like the Pah-tson 
body, and indeed like the neighboring granites of Truckee and Granite 
ranges, this mass is unmistakably structureless. 

Granite Raner.—The region in the northwest corner of Map V., 
representing the limit of our labors in that direction, is occupied by an 
extensive table-land of basalt known as the Madelin Mesa. Its eastern 
boundary abuts against a sharp, high ridge of granite which enters the area 
of the Fortieth Parallel Exploration from the north, and extends south- 
ward twenty-five miles to the region of Mud Springs and Granite Creek 
Station. It is a from eight to twelve miles wide, rising at its culminating 
points to 6,000 feet above the level of the desert Excepting the volcanic 
rocks which skirt its base upon the east and west, it is wholly com- 
posed of a single mass of granite, of decidedly uniform texture, and 
producing, both in the spurs and in the dominating peaks, only rounded 
and dome-like forms. On the extreme heights northwest from Granite 
Peak Station, imperfect conoidal structure is developed. From Truckee 
Range, whose extreme northern point almost comes in contact with the 
Granite Range body, it is separated by a strip of level desert. This is 
rather a topographical than a geological separation, because Truckee Range 
for many miles to the south is itself made up, as will be seen hereafter, of 
a precisely similar granite. So far as examined, Granite Range consists of 
a rock having all the features of the neighboring masses of the Truckee, 
Pah-tson, and Sahwave Mountains. The rock possesses an even, middle- 
grained texture, breaking quite readily under the hammer. In composition 


94. SYSTEMATIC GEOLOGY. 


it is a mixture of either white or translucent grains of quartz, orthoclase, 
plagioclase (probably albite), biotite, hornblende, and frequent hair-brown 
and golden-yellow titanite. Many of the plagioclases have extremely bril- 
liant surfaces, upon which are traced the characteristic twin striations. As 
usual in this family of granites, the hornblende and mica are most variable. 

TruckEE Rance—The Archean exposures of Truckee Range lie 
wholly to the north of Nache’s Pass. From that depression to its northern 
extremity in the region of Mud Lakes, the range is nearly a continuous 
body of granite, with a few limited outcrops of Archean schists and an 
unimportant mass of Triassic slates, together with a great development of 
Tertiary volcanic rocks in the region of Nache’s Pass. The Archzean body 
is composed of schists and of granites representing two periods of forma- 
tion. First in order will be described the limited occurrence of schists. 

In the region of Nache’s Peak, directly on the 40th parallel, at the 
east side of the range, and lying in immediate contact with the main granite 
body, is a development of Archzean schists which occupy the eastern foot- 
hills of the range for about nine miles. Among these, one from the 
summit of Nache’s Peak deserves special mention. To the naked eye it 
presents the appearance of a fine microcrystalline stone, in which no indi- 
vidual particles are determinable. Under the microscope it appears as a 
fine-grained mixture of plagioclase and hornblende with a little quartz. 
Although without much doubt a metamorphic rock, and essentially a mem- 
ber of a series of schists, it has exactly the composition of a slightly quartz- 
iferous diorite. It is indeed mineralogically the counterpart of those dio- 
ritic gneisses already described in Medicine Bow and Park ranges, as well 
as in the Wahsatch and Humboldt. But it has this distinction, that its par- 
ticles are relatively very much finer than those of any of the dioritie schists 
in the ranges far to the east. South of Nache’s Peak the series seems to 
be made up of dark mica schists having a decidedly fissile structure, and 
composed, like the dioritoid rock above mentioned, of exceedingly fine- 
grained particles. It is essentially made up of minute granules of quartz, 
with biotite and muscovite. Zones of fine, dark, steely-gray quartzitic 
schists are also interstratified with the other beds. In some of the banded 
quartzitic rocks, in which white and nearly black layers repeatedly alter- 


ARCHAZAN EXPOSURES. 95 


nate, the microscope discovers that calcite is present in numerous brilliant 
crystals. Two or three miles west of Luxor Peak, in the northern part 
of the range, is exposed a small body of Archzean schists; and again twelve 
miles to the north the granite is flanked by a narrow belt of schists, a mile 
and a half wide by six miles long, placed with the strike of the range. 
Both these unimportant northern exposures are accompanied by outflows of 
basalt, which mask their dip toward the plains of Mud Lake. Neither out- 
crop possesses any especial geological interest, except as indicating a con- 
siderable extension for the schists of the range. It would seem that in many 
of these western Nevada ranges the structure is that of a simple anticlinal, 
having a broad, massive granite core with crystalline Archean schists dip- 
ping away from either flank. Subsequent erosion has removed a great 
amount of the schists, and the horizontal Tertiary and Quaternary beds have 
so buried the flanks of the ranges that only small portions of the old schists 
are visible. Could the horizontal and overlying beds be all removed, there 
would doubtless be found a great amount of crystalline schists. The litho- 
logical resemblance is so intimate, and the area over which they are exposed 
is in reality so limited, that all these detached outcrops of schists may be 
thrown into one series, which formerly extended over the whole country. 
Their resemblance is more intimate when correlated by the mechanical con- 
dition than by their mineral composition. 

Southeast from Winnemucca Lake is a small body detached from the 
main granite mass of the range, flanked along the east by strata referred to 
the Trias, and on the north and south by outflows of rhyolite, the western 
slope plunging beneath the Quaternary plain. The rock bears the aspect of 
a readily crumbling metamorphic granite, and is composed chiefly of quartz, 
flesh-red orthoclase, and a few minute crystals of plagioclase. The only 
mica is muscovite, and that occurs in so small a percentage, and is so un- 
evenly disseminated through the rock, as to justify the term “‘aplitic granite.” 
A further specimen from the same body is made up of quartz, partially 
decomposed orthoclase and plagioclase—the former much the more abundant 
of the two—and a little regularly disseminated biotite. The muscovite-bear- 
ing granite of this body seems to be the older of the two. 

North of Nache’s Peak, the main range, as well as the accompanying 


96 SYSTEMATIC GEOLOGY. 


body of the Sahwave Mountains with which it is solidly connected, is com- 
posed, so far as known and wherever we have visited it, of a dioritoid 
species of granite. It is of a medium grain, varying from a yellowish-gray 
to a pure bright-gray, and is noteworthy from the rarity of its disconnected 
divisional planes. It is made up of quartz, orthoclase, plagioclase, biotite, 
hornblende, and titanite. The microscope, as usual, also shows a few small 
crystals of apatite. Here, as in the other bodies of this particular type, 
every mineral component of the rock seems to be nearly uniformly dissem- 
inated through the mass. As a whole it is a granite characterized by rela- 
tively very high percentages of hornblende, mica, and plagioclase. The 
minerals are comparatively fresh and undecomposed, and the plagioclase 
is more nearly related to albite than to oligoclase. 

Quartz veins and fine-grained granite dikes traverse the coarser mass of 
Truckee Range, in many places carrying more or less massive black horn- 
blende. Hot Springs Butte is a detached continuation of the range just 
beyond its northern extremity, near the borders of Mud Lake Desert. It 
is a single knob of granite, of the dioritoid type, rising 1,000 feet above 
the Quaternary plain. 

Lakk Raneu.—That portion of Lake Range which lies north of Pyra- 
mid Lake consists essentially of a central body of granite broken through 
and surrounded on the south by fields of basalt which slope to the shore 
of the lake. On its eastern exposure, from near the lake shore to a point 
four miles north of Pah-Rum Peak, it is overlaid by a series of dark 
shales, which have been referred to the Jurassic age. Northward, save for 
a few basaltic interruptions, the granitic mass extends between the two 
valleys of Mud Lake Desert until it is bounded on the north by a body of 
gneisses, which it penetrates like a tongue. The Archzean body is about 
twenty-four miles from north to south, with an extreme width, in the 
neighborhood of Pyramid Lake, of ten or twelve miles. The granite is of 
the hornblende-plagioclase type, and does not differ from that so fre- 
quently occurring in contiguous ranges. In gneisses at the northern end 
is. observed a singular mineralogical analogy to the associated granite. 
But they possess a distinctly gneissoid structure, and are distinguished 
from the near granite by the absence of titanite. They are composed of a 


ARCHASAN IXPOSURES. 97 


very fine-grained mixture of quartz, plagioclase, parallel-arranged mica 
(probably biotite), and considerable hornblende. The microscope reveals 
apatite, and also the fact that the quartz granules are very poor in liquid 
inclusions; two characteristics which would seem to establish a parallelism 
between the granite and the gneiss. It is, however, quite similar in compo- 
sition to many of the gneisses already described in the Wahsatch, Humboldt, 
and Rocky Mountain regions, except that it is very much finer-grained, as 
are all the metamorphic sedimentary rocks of the Archzean in western Ne- 
vada. It is essentially a dioritic gneiss, containing considerable quartz and 
mica. The mineral constituents have a remarkably fresh, brilliant appear- 
ance, common to nearly all the schists of the neighborhood. 

Peavine Mountaty.—In the southwest corner of Map VY. is an Archean 
body, lying a few miles north of Truckee River, and sweeping up from the 
valley of that stream in bold slopes to the dominant point of Peavine Moun- 
tain, which has an altitude of 8,217 feet. The body measures a dozen 
miles from east to west, by about seven miles from north to south. On 


the north it is entirely surrounded by granite, on the south the inclined 
strata of the Truckee group of Miocene rest against it, and the eastern end 
is overflowed by a mass of Tertiary andesite. The whole mountain is 
built of a series of conformable, highly altered beds, striking from north 
50° to 65° east, which consist for the most part of fine-grained quartzite 
strata, riven in every direction with minute fissures, which are filled with a 
ferruginous material. The less decomposed parts of the quartzite carry 
small grains of magnetite and occasionally a little yellowish-green epidote. 
It is obviously the decomposition of magnetite which produces the iron in- 
filtration, giving the prevalent yellow color to the body. ‘The felsitie beds 
contain similar iron seams, and are likewise much discolored by the products 
of decomposition. In the region of the Bevelhymer Ledge there is an ob- 
scure occurrence of rock which retains a fresh, undecomposed appearance, 
made up of dull, opaque orthoclase, some plagioclase, a little hornblende, 
and mica. It seems to be of eruptive origin and to indicate a sort of con- 
necting link between syenite and diorite. 

CauirorniA BorpEr.—F rom Peavine Mountain Pass to State Line Peak, 
and from the western boundary of the map as far east as Louis’ Valley, ex- 

7K 


98 SYSTEMATIC GEOLOGY. 


tends an irregular mass of granite which is topographically varied by wind- 
ing ridges, the whole being invaded by irregular valleys of Quaternary, 
which are, in truth, nothing more than the modern material disintegrated 
from the neighboring granite hills and washed down into basin-like depres- 
sions. The region has not received sufficient study to make it certain that 
all the granite is of one type; but as far as observed it seems to consist of 
quartz, orthoclase, plagioclase, biotite, and hornblende; and in all thin see- 
tions examined the microscope reveals a plenty of apatite crystals. There 
are no indications of a metamorphic origin of this general body; on the 
contrary, it possesses all the appearances of a granitic extrusion, and is no 
doubt intimately related to the granite mass of the Sierras. On the ridge 
opposite Spanish Springs Valley occurs an exceedingly fine-grained variety 
of granite porphyry, in which the individual minerals cannot be recognized 
by the naked eye. The microscope reveals quartz, orthoclase, beautifully 
striated plagioclase, biotite, and shattered, imperfect crystals of hornblende. 
It would seem to be a porphyritic condition of the neighboring granite, 
differing only by the minuteness of its particles. 


SiC wo Th. 
CORRELATION OF ARCOHZAN ROCKS. 


By referring to Analytical Geological Map L., at the end of this chapter, 
the reader will observe five Archzean districts where exposures are indicated 
in the characteristic map-color of that age, namely: the Rocky Mountains, 
including those portions of Colorado and Park ranges within the limits of 
this Exploration, as well as the whole Medicine Bow Range; Red Creek 
region, on the north flank of the eastern end of the Uinta Mountains; the 
Wahsatch core and neighboring Archean islands; middle Nevada District, 
comprising the Humboldt Range body, Kinsley District, and Franklin Buttes; 
and western Nevada District, embracing the schists of Montezuma and 
Truckee ranges and the quartzite of Peavine Mountain. All other expo- 
sures of Archzean age are colored as granites. The intention of this dis- 
tinction is to separate those formations which are of sedimentary origin 
from the class of eruptive rocks. 

Two causes prevent the drawing of such a line with entire precision: 
First, there is a frequent doubt as to the true nature of certain granitoid 
rocks which are allied on the one hand to eruptive granites by mineralogi- 
cal constitution as well as by a broad concentric structure, but related on 
the other hand to a series of gneisses whose bedding and passage into dem- 
onstrably sedimentary beds mark the granitoid member as only the ex- 
treme form of a series increasingly metamorphosed in depth. These ques- 
tionable rocks, where well shown, as in the case of the Laramie Hills, have 
almost invariably been considered by us to be of metamorphic nature and 
classed with the series of clastic origin. A second difficulty is encountered 
where limited bodies of granite are exposed under unaltered sedimentary 
beds, as throughout Nevada. Such masses, showing no trace of sedimentary 
origin, and quite disconnected with any crystalline schists or other Archean 
sedimentary rock, especially where the arrangement of their constituent 
minerals is after the granitic habit, have been called simply granite, with a 
general belief that they are of eruptive origin. The further erosion of over- 

99 


100 SYSTEMATIC GEOLOGY. 


lying rocks might in many cases reveal such relations with crystalline schists 
and gneisses as to compel the belief that the granites are metamorphic. 
Again, among those colored as granite a majority are instances of unmis- 
takably intrusive origin. The distinction indicated on the map is therefore 
only approximately true. 

It is not easy to analyze those subtle appearances which lead the ob- 
server to incline to one or the other of the two possible modes of origin of 
a granite outcrop. Parallelism of bedding, and even parallelism of the ar- 
rangement of minerals, are consistent with the theory of an eruptive origin. 
Certain passages of gneissoid granite appearing in the great eruptive granite 
body of the Sierra Nevada show quite as much parallelism of bedding 
and internal arrangement of minerals as the Rocky Mountain granites 
to which we have assigned a metamorphic origin; yet the Sierra field, 
as a whole, is clearly eruptive. But at the same time, in the intimate 
arrangement of the mineral particles, and in the mode of contact between 
the various mineral ingredients, there is a certain broad uniformity in all 
the eruptive granites which produces a characteristic impression upon the 
eye. On the contrary, the granites which we conceive to have been of 
metamorphic origin, no matter how simple the mineralogical composition, 
have always a peculiar variability of arrangement; and even in the ab- 
sence of any pronounced parallelism, they show the effect of interior 
compression and irregular mechanical influences. On the one hand, in the 
eruptive granites there seems to have been a steady expansive force, 
doubtless due to the heat and elastic fluids, which gave to all the particles 
a certain independent polarity, while in the metamorphic granites they 
seem to have been crowded into constantly conflicting positions. As the 
result of this, the crystalline particles of the metamorphic granites are 
much less apt to have completed their crystallization, or, if it was com- 
pleted, they have been crushed and torn asunder and their particles scat- 
tered, while in the case of the eruptive granites crystallization seems to 
have been more perfected. The result of this is to give to the eruptive 
granites something of the uniformity of texture of a volcanic rock, while all 
the metamorphic granitoid rocks, when once the gneissoid parallelism of min- 


erals is broken up, have a crushed, irregular, and confused mode of arrange- 


CORRELATION OF ARCHAIAN ROCKS. 101 


ment. Under the microscope especially, there is usually observed a con- 
siderable difference between the two types, in the amount of dislocation 
and of intererystalline movement or crushing, the structureless granites 
often containing perfect hexagons of biotite or completed hornblende, while 
in the gneissoid granites a defined crystal of one of the less coherent con- 
stituents rarely if ever appears. 

Meramorpnic Rocxs—In Colorado Range are two typical series 
which in all probability are unconformable. The lower, as already shown, 
consists of gray and pearl-colored aplitic granites with metamorphic facies, 
overlaid by a red granitoid member, having little parallelism of interior 
arrangement or evidence of stratification beyond a general tabular bedding, 
also decidedly aplitic, though carrying rather more mica than the gray 
variety. Over this lies a third member, very red, with an extremely 
variable but small amount of mica broadly but distinctly bedded. A simi- 
lar series is observed in the Black Hills and recurs in Park Range. A 
small granitoid body in Mill Canon, Wahsatch Range, is referred to this 
series. The whole group is essentially made of quartz, orthoclase, oligo- 
clase, very little biotite, rare muscovite and lepidomelane, and extremely 
little hornblende, with accessory masses made up of labradorite, diallage, 
ilmenite, graphite, and magnetite. Taken with the dependent development 
of gabbro, ilmenite, magnetite, and graphite, the resemblance to known 
Laurentian bodies is so strong that we have little hesitation in referring our 
series to that age. In this connection the assignment by Dawson of closely 
similar rocks in Manitoba and British Columbia should be remembered. 
If, as we suppose, these exposures represent all the metamorphic Lauren- 
tian within our area, it is a very noticeable fact that limestones, dolomites, 
quartzites, conglomerates, pyroxene rocks, and the various hydrated Lau- 
rentian forms are wanting, and that among the irruptive species gabbro 
and felsitie porphyries only occur. A little chlorite is the only representa- 
tive of the hydrated minerals. A rude estimate would place the thickness 
of the series at about 25,000 feet. 

A second and equally well characterized series of metamorphic rocks 
is found in the upper horizons of the Medicine Bow, and also in the higher 
members of Park Range, Red Creek in the Uinta, the Wahsatch and Salt 


102 SYSTEMATIO GEOLOGY. 


Lake islands, and the exposures in the Humboldt Mountains, Franklin 
Buttes, and Kinsley District. Probably to these localities should be added 
a portion of the gneiss, schist, and quartzite formation of Colorado Range, 
south of our map. 

This series consists of true gneisses, often decidedly granitoid, and 
made up of quartz, orthoclase, biotite, rare muscovite, and plagioclase, asso- 
ciated and repeatedly interstratified with mica schists, both of biotite and 
muscovite, the white mica beds sometimes carrying garnets; hornblendic 
schists, in places pure amphibolite, and again amphibole and quartz, with 
either orthoclase alone or plagioclase alone, or the two associated. Some- 
times the hornblende unites with plagioclase to form a true dioritic gneiss. 
In several of the hornblende rocks where mica is either absent or plays a. 
minor role, zircon is present in minute crystals, visible under the microscope 
only, but freely disseminated through the mass. The above described series 
is exposed certainly 12,000 or 14,000 feet thick in Wahsatch Range, about 
the same in Humboldt Range, and probably somewhat less in Park and 
Medicine Bow ranges; but in the Clear Creek region of Colorado Range it 
shows not less than 25,000 feet. 

Conformably overlying this group is a thick development of argillites, 
siliceous schists (carrying in places a hydrated chloritic mineral, and verging 
toward the nacreous schists of Canada), jaspery conglomerates with a fine 
siliceous matrix, iridescent hornblende schists, quartzites more or less rich in 
minute feldspar crystals and carrying also a variable amount of muscovite 
and chlorite, and finally white or gray dolomitic marbles. 

The upper part of the series seems to be variable in the sequence of its 
members and in thickness. The best exposures occur in the Medicine 
Bow, where there must be between 3,000 and 4,000 feet. 

The whole series—gneisses, amphibolites, dioritic gneiss, garnetiferous 
mica schist, and zirconiferous amphibolite schist, quartzite, and limestone— 
occurs in the Medicine Bow and Humboldt. The lower or gneiss and am- 
phibolite schist portion is represented in Park Range, in the Wahsatch, as 
also probably in the schist zones overlying the granitoid Laurentian part 
of Colorado Range. 

At Kinsley District and Frankiin Buttes are observed only the upper 


CORRELATION OF ARCHASAN ROCKS. 103 


limit of the gneiss (here porphyroidal), together with white dolomite; the 
same association and intercalation as at Mount Bonpland in the neighboring 
Humboldt Range. The Archeean islands of Salt Lake, which were not 
especially examined by us, evidently belong to the same series. 

Argillites are best developed in the Medicine Bow and Salt Lake islands. 
As a whole, this second series bears more than a superficial resemblance to 
the Huronian of Canada, and to that age, with some hesitation, it is pro- 
visionally referred. G. M. Dawson, finding essentially the same two series 
in the Rocky Mountains, near the 49th parallel, makes the same reference. 
With the Huronian is classed also the Red Creek exposure of quartzite, 
dioritic schists, and paragonite rocks, carrying garnet, staurolite, and cya- 
nite; so also, a limited area of intensely metamorphosed quartzite at Pea- 
vine Mountain, near the California boundary. 

Between the rocks thus referred to Laurentian and Huronian ages, 
there is a characteristic difference in the intensity of metamorphism and 
obliteration of original structure. The former are essentially granitoid in 
type, and show lithological changes only when examined over considerable 
areas, or up and down through a rather wide vertical range. Bedding is 
wanting, except in the upper members, and even there it is rather of the 
character of a tabular structure, made up of beds varying from a foot to 
five feet in breadth, than a true stratification. On the other hand, the sup- 
posed Huronian zone is always distinctly, often minutely, stratified; and, 
moreover, a conspicuous feature is the permanence of the mineral charac- 
ter of beds over considerable distance. 

Gradual changes are observed in the mechanical condition of single 
beds. They may be characterized in one place by fine-grained, minute 
crystallization, in another by the assemblage of very coarse, large particles. 
Ilere is seen a strict parallelism of the mica or amphibole particles; a little 
way off, owing to inequalities of pressure and consequent interior mechani- 
cal rearrangement, the constituent minerals may possess the mode of aggre- 
gation of a granite or porphyry. Observed over great distances, it is true 
that changes are detected in the chemical character of a given bed, but here 
the limit of change ends, and we fail entirely to observe any of those rapid 
mineralogical fluctuations so frequently noted by some other students of 


ay aye vey Pr 
Cordilleran geology. 


104 SYSTEMATIC GEOLOGY. 


As between the different contiguous beds of the series, there is indeed 
a constant variability shown. Every conceivable permutation possible to 
quartz, mica, hornblende, orthoclase, and plagioclase seems to be brought 
out and repeated again and again; but within the limits of a single bed the 
chemical and generally the mineralogical constitution are rigidly preserved. 
. Even in the single exception to this, where chloritic matter replaces by 
pseudomorphosis either garnet or mica, the alteration is strictly confined to 
the affected bed, never in a single instance clouding off into the bounding 
strata. 

Where the stratification is thin, and where irregularly crumpled regions 
have been eroded, there is often great difficulty in identifying or following 
2, given bed, existing surfaces often showing a very gentle bevel of the edges 
of the members of a series of strata. So in passing from one to another it 
is many times hard to determine the divisional plane, and hence probably 
the cause of such expressions as “this mica schist passes rapidly into a 
syenite,” or ‘this hornblendie schist in a few feet passes by imperceptible 
gradation into an orthoclase granite.” 

Whatever changes occur within a given stratum of the crystalline 
schists, even including the pseudomorphism of hydrated chloritic minerals 
after anhydrous silicates, are due to a mere mechanical or chemical re- 
arrangement of particles within the bed, and there is no tendency whatever 
to break up the chemical constitution of a given stratum, no disposition 
on the part of a stratum to scatter its minerals up or down into adjacent 
beds. Instances of this permanence of constitution are constantly seen in 
single zones of dioritic gneiss or of pure black amphibole rock, lying 
between white quartzites, without a trace of hornblende one inch from 
the main bed; or a garnetiferous muscovite gneiss enclosed in a biotite 
gneiss, never with the least tendency for the garnets to straggle up or down. 
In the heavy white quartzites of Humboldt Mountain there are garme- 
tiferous zones and muscovite-bearing zones, but they are rigidly confined to 
their own horizon. Whatever, therefore, may have been the cause which 
rendered the original sediments crystalline, it failed to impregnate one zone 
with the chemical elements of its neighbor. Evidences of metamorphic alter- 


ation, such as results in other Archean regions in the production of taleose 


CORRELATION OF ARCHASAN ROCKS. 105 


bodies, are almost altogether wanting. A protogenoid granite of limited 
extent indeed occurs on War Eagle Mountain, Owyhee District, Idaho, and 
also in immediate contact with mineral veins in Colorado Range; but 
these are obviously due to the action of very modern causes and are re- 
stricted so closely to fissured regions as rather to fall under the head of vein 
phenomena. 

The appearance, on a microscopic scale, of chlorite after garnet in 
the beds of the Wahsatch and Humboldt, is paralleled in a large way in 
Archean schists observed by the writer near the head of Santa Maria 
River in Arizona, where large garnets, equal in size to those described 
by Pumpelly on Lake Superior, are changed into a pale-green chloritic 
mineral. 

Slaty hematites are seen feebly represented in the schists of Ralston 
Creek, Colorado Range, under the quartzites. The specular-iron schists 
which occur in the region of Prescott, Arizona, are wanting in the Fortieth 
Parallel area. 

The mechanical disturbances that have taken place within given 
beds which are simple and comparatively unchanged as to their chemical 
nature, seem to be worthy of a second mention here. In treating of the 
Wahsatch and Humboldt, it was said that certain beds show a passage from 
a parallel arrangement of minerals to a granitoid mode of disposition of 
particles. In the varying dip, sinuous strike, and deep bellying down of 
certain folds, there is abundant evidence of irregular mechanical strain. 
The general shrinkage of beds by superincumbent weight is a phenomenon 
too well known to need description here, but besides this there is often 
ample evidence of longitudinal compression. The strata of dioritic eneiss, 
true gneiss, mica schist, and even so compressible a rock as quartzite, show 
an interior erumpling, already described in detail, which breaks up the par- 
allel schistose arrangement of particles and squeezes the minerals into a 
granitoid irregularity. It is evident that great longitudinal compression, 
due to the sagging down of a very thick series when brought to bear in a 
group of beds, does not meet so sharp a resistance as to produce a crushing, 
or even a very localized effect ; but the strain is relieved by a wide-spread 


readjustment of particles, after the manner of eranite. 


106 SYSTEMATIC GEOLOGY. 


In the Humboldt gneisses, and conspicuously in the dioritie gneisses 
at the mouth of Ogden Caron in the Wahsatch, this phenomenon may be 
most interestingly observed. It should be said that this effect has gone no 
further in our Huronian rocks than the destruction of parallelism within 
beds. This being true of rocks which have not been subjected to very 
intense and complex disturbance, it would seem only necessary to heighten 
and magnify the action to obliterate the parallel structure through great 
masses and produce out of bedded rocks, by mechanical means alone, 
many of those puzzling granitoid forms which by certain subtle, difficultly 
analyzed appearances, give to the field observer the impression of a meta- 
morphic origin. How else than by crushing of the constituent particles 
can we account for those grains of quartz which have upon their periphe- 
ries the open pits that could only have been formed as the walls of fluid 
inclusions? The above suggestions are not intended to have a positive 
application beyond the gentle action described in our supposed Huronian 
beds, but only to indicate that the precise limit of purely mechanical action 
on already crystallized schists is at present unknown, and that it may pos- 
sibly include the comminuted granitoid Laurentian rocks. 

It would be altogether unsafe to make from the character of the Ar- 
chean outcrops of the Fortieth Parallel a generalization as to the fundamental 
rocks of the whole United States Cordilleras. In the wide areas which are 
still unexamined geologically, there is ample room for a repetition of all the 
Appalachian phases. At the same time one cannot fail to notice the wide- 
spread simplicity of petrological forms, the prevalence of granites, granitoid 
eneisses, and dioritic metamorphic rocks, the paucity of argillites, quartzites, 
limestones, and zirconiferous and staurolite schists, the infrequence of large 
bodies of magnetic, specular, or spathic iron, and the complete absence of 
corundum, chrysolite, serpentine, steatite, pyroxene rocks, the true nacreous 
schists, and other minor forms observed in the Appalachian system. 

Without doubt, the most interesting laws which come out of the compari- 
son of these exposures are, that when considered in depth, from the upper- 
most limits of our so called Huronian to the lowest Laurentian exposure, 
there is, first, a regular, steady increase of the intensity of metamorphism, and 


secondly, a pretty regular increase in the thickness of individual members 


CORRELATION OF ARCHAZAN ROCKS. 107 


of the series. The lowest Laurentian aplitic granitoid bodies of the Laramie 
Hills are the heaviest beds and the most changed from their original sedi- 
mentary condition. The higher Huronian group of gneisses, quartzites, con- 
elomerates, dolomites, and argillites are at once the most thinly bedded and 
least metamorphosed. Individual beds remain as specialized as the day 
they were deposited. At the lower exposures of the whole Archean forma- 
tion well defined crystals are of great rarity; even microscopic apatite, the 
best presented species, is generally crushed and dislocated; micas are dis- 
torted, and all feldspars are more or less fragmentary. A marked con- 
trast is observable at the upper extreme. Here many micas, hornblendes, 
garnets, and even feldspars are nearly if not quite completed crystals. 
The exceptions to this are those places already described, where local 
compression has broken up the original arrangement of the crystalline 
ingredients. 

The western Nevada schists are exposed as a series, never over 4,000 or 
4,000 feet thick, of rocks whose constituent particles are in a fine state of 
subdivision. They are largely compounds of quartz, muscovite, and biotite, 
or quartz and hornblende. Feldspars are rare, and in most cases all the 
crystalline ingredients are only resolvable under the microscope. Appended 
to this section is a table of analyses of metamorphic rocks. 

Granrres.—Leaving out of consideration those forms which are 
deemed to be of metamorphic origin, the eruptive granites will be seen by 
reference to the map accompanying this chapter to be, so far as the belt 
of the Fortieth Parallel is concerned, situated west of longitude 111° 30’, 
or west of the east base of Wahsatch Range. Nearly every considera- 
ble mountain body between the Wahsatch and the California line shows in 
the lower horizons exposures of one or more bodies of granite. A petro- 
logical comparison of these exposures leads to a classification into four 
distinct groups. 

The first type consists of quartz, orthoclase, a few minute and unim- 
portant crystals of plagioclase, and muscovite, with a small but variable 
percentage of microscopical apatite. The granites of this type are all west 
of Reese River, longitude 117°, and in each case are associated with the 


western Nevada type of Archiean schists, consisting of a very fine micro- 


108 SYSTEMATIC GEOLOGY. 


crystalline combination of quartz, biotite, muscovite, and magnetite, or 
quartz, hornblende, and magnetite. Muscovite granite occurs at the Ravens- 
wood Hills in Shoshone Range, and in the Pah-tson Mountains, where it 
contains pegmatite passages made up of the same minerals as the granite, 
only on a far larger scale of crystallization. A third outcrop of musco- 
vite granite is in Truckee Range, in the body southeast of Winnemucca 
Lake. This last named locality has been but little studied, and is chiefly 
surrounded by outpourings of Tertiary volcanic rocks, and its relation with 
other members of the Archzean series is altogether unknown. As to the 
age of the granites of this type, we have practically no adequate data. At 
Ravenswood Peak the muscovite granite is intimately involved with the 
upturned crystalline beds, and is clearly overlaid unconformably by the 
rocks of the Carboniferous. There is little doubt of its Archaean age, but 
its reference to that period is only on general lithological grounds. 

The second type consists of quartz, orthoclase, little plagioclase or 
none at all, biotite, and microscopic apatite. It is essentially a granite, like 
type the first, with the substitution of biotite for muscovite. It has a 
rather wider range than the other, making its first appearance in Ombe 
Range, west of Salt Lake Desert, and reappearing westward to the Cali- 
fornia line. It is found in Ombe Range, at Nannie’s Peak in Seetoya 
Range, at Mount Tenabo in Cortez Range, in the neighboring Wah-weah 
Mountains, in the granite body of Montezuma Range lying east of Antelope 
Peak, and finally in the hills southeast of Winnemucca Lake, Truckee 
Range, where it is associated with the muscovite granite of the first type 
As in the first type, the microscope always reveals a small but varying pro- 
portion of minute apatite. 

The third type consists of quartz, orthoclase, little or no plagioclase, 
biotite, hornblende, and microscopic apatite. Its distribution is co-extensive 
with that of the second type. It makes its first appearance in the Goose 
Creek Mountains, a little east of the 114th meridian, and reappears at. 
intervals (often in close proximity to the granites of the second type) 
westward to the 120th meridian. It is developed at Goose Creek; at 
Granite Cation in Cortez Range; near the head of Susan Creek in Sectoya 


Range; at Shoshone Knob and the Wood Ranch Canon, both in Shoshone 


CORRELATION OF ARCHASAN ROCKS. 109 


Range ; at Granite Point, Augusta Mountains; in the Havallah; near Spauld- 
ing’s Pass, Pah-ute Range; at the Montezuma mine, and in Montezuma 
Range west of Rye Patch Station. It is distinguished from the second 
type by the presence of hornblende. 

The fourth type presents the most complex petrological features of any 
of these families of granite, and consists of quartz, orthoclase, plagioclase, 
which is often equal in quantity to the orthoclase, and sometimes exceeds 
it, usually a high percentage of biotite, with an equal proportion of horn- 
blende, titanite visible to the naked eye, and a high proportion of micro- 
scopic apatite. The rocks of this group display their minerals usually in a 
very fresh, undecomposed condition. In general, the rocks differ from 
those of the third type by the presence of macroscopic titanite, and by the 
high proportion of plagioclase and hornblende, which sometimes dominate 
over the orthoclase and biotite, and throw the affinities of the granite toward 
a diorite. Indeed, there is but little difference between those diorites 
that are unusually rich in orthoclase, mica, and quartz, and the granites 
of this type, which have an uncommonly high proportion of hornblende and 
plagioclase. The presence of titanite is not a distinguishing feature, for 
some of the diorites possess that mineral in the same proportion as the rocks 
of this group. So, too, microscopic apatite is common to both rocks. In 
the previous type the plagioclase always, or nearly always, approaches 
oligoclase ; in the present type it is often albite. While the granites of this 
group are perhaps the most prominent as regards geographical distribution 
of the truly eruptive varieties observed by the writer in the system of the 
Cordilleras, and while they possess a great uniformity of appearance from 
the Wahsatch to the Sierra Nevada, it is true that those dependences of 
diorite which mineralogically approach it are of extremely rare occurrence, 
and are always so related to dioritic masses as to be clearly recognized as a 
dioritic variety. There is therefore little danger of ever confounding the 
granitoid diorite with the extremely dioritic members of the fourth type. 

This classification, based upon field observations, is interestingly car- 
ried out by Zirkel, whose microscopic examinations in every way confirm 
the field arrangement. To his interesting chapter on granites the reader 


is referred for those minute yet important interior phenomena which char- 


110 SYSTEMATIC GEOLOGY. 


acterize the granites of all these families. The table of analyses of the 
eruptive granites accompanying this section gives a single instance of the 
second type, that of Nannie’s Peak ; two of the third type, from Shoshone 
Knob and Wright’s Cation; and the remainder of the table is devoted to 
the rocks of the fourth type. Of these latter it is seen that the range of 
silica embraces the extreme members of the series, that of Agate Pass 
reaching 75 per cent.; while in the Wachoe granite the silica is only 553 
per cent., representing with one exception the most basic granite of which 
there is any published analysis, and with the one referred to, that of Ar- 
dara, described in Haughton’s paper on the rocks of Donegal,* it is almost 
identical in composition, both chemically and mineralogically. In general 
the granites of the fourth type in Western Nevada are rather basic, the 
rock of El Capitan in Yosemite Valley furnishing about the normal chem- 
ical type. 

When seen in appositions which give a clew to the relative ages of the 
several types, it is found that they occur in the order given, the muscovite 
being the oldest, the dioritoid variety the youngest. Passing from muscovite 
to dioritoid species, the chemical acidity declines to a minimum in the 
Wachoe occurrence. 

In denominating these groups of granite as eruptive, it is only intended 
to indicate that in their relations to the contiguous Archzean schists they 
have the appearance of intrusive bodies, and that in their interior structure 
and general mode of occurrence there are none of those evidences of alli- 
ances to the crystalline schists which are observed in the granitoid gneisses 
of so many localities, especially in the Rocky Mountain region. In so- 
called eruptive granites there is neither parallelism of general bedding nor 
of interior arrangement of the minerals, and the most ordinary phenomenon 
of structure is the development of conoidal shapes formed of concentric lay- 
ers varying in thickness from a few inches to 100 feet. This structure, so far 
as observed, is strictly confined to the hornblende-bearing granites, and 
never makes its appearance in those of the first and second types. 

While among the rocks of the Fortieth Parallel this phenomenon of 


conoids is only obscurely shown, in the great hornblende-plagioclase body 


* Transactions of the Royal Irish Academy (1859), Vol. XXIIL., p. 608. 


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TABLLEL, 


Number of 
analysis. 


~ 
+ 


2S) 


16 


U7 


18 


19 


20 


21 


22 


Locality. |Remarks. 


23 


Wachoe Mountains ~ Jaring liquid inclusions, orthoclase 
Il. unaltered plagioclase, large indi- 
ide and biotite, microscopic apatite, 
black microlites. 


Granite Peak, East R sions, orthoclase, much p!agioclase, 


Mountains ite, and frequent macroscopic titan- 
apatite. 


Hills west of Granite Cr in inclusions than granite given 
Nevada ne same mineral composition. 


Shoshone Knob, Shosho).... little plagioclase, hornblende, 


broscopic apatite. 


Wosemites Valleys HIsCatcusions: orttociasesaibite biotite 


, apatite. 


Canon north of Wrigh)nausions, orthoclase, rare plagio- 
West Humboldt opic apatite, zircon!! 


Egan Cajon, Egan Ranhsiderable plagioclase, biotite, spar- 


Nannie’s Peak - - - hlusions, carrying salt cubes, ortho- 
\ttle biotite, microscopic apatite. 


Cottonwood Canon, Wahiclusions, orthoclase, much plagio- 


e, biotite, titanite, apatite. 


Agate Pass Canon, Cortedich plagioclase, hornblende, rare 


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CORRELATION OF ARCHASAN ROCKS. ila 


of the Sierra Nevada, which is both geographically and mineralogically the 
characteristic occurrence of this type of granite, the dome forms assume a 
most imposing scale and become some of the most prominent topographical 
features in the granite area. So far as these concentric conoidal shells 
throw light upon the outbreak of the granite, they seem actually to indicate 
something like the original form due to violent extrusion of the plastic 
though not fluid bodies. 

Although instances of each granitic type are found unconformably 
underlying the low members of the Paleozoic series, this is not the case 
with each outerop; many granitic masses are found unconformably under- 
lying Mesozoic or even Tertiary yoleanic rocks. But there is absolutely 
no evidence whatever in favor of the belief of granitic extrusions later than 
the Archean age. With so many mountain ranges deeply fissured and 
faulted, broken and thrown into all conceivable positions, there would seem 
to be abundant exposures to find intrusions of granite into the crevices and 
fault-fissures of the post-Archzean formations, if such existed. None have 
been discovered in the Fortieth Parallel area. 

Great simplicity is given to the relation of the two series by the unal- 
tered and conformable conditions of the whole Paleozoic strata. Intrusions 
of granite into sedimentary strata other than Archzean crystalline schists, 
such invasions as are brought io light by Whitney in the Sierra Nevada, 
where granite invades the highly altered ‘Triassic and Jurassic strata, are 
wanting. 

As an instance of how dangerous any attempt to correlate age by 
petrological features alone really is, may be cited the Jurassic granite of 
California and the granite of the Cottonwood region on the Wahbsatch, 
which is unmistakably Archzean. They are positively identical down to the 
minutest microscopical peculiarity. 

Very many of the exposures laid down on the map are known to be 
Archean by position. In the remaining cases there is no proof that they 
are not Archean. The absence of evidence of disturbance throughout the 
Paleozoic, or of granitic intrusion anywhere in the post-Archzean forma- 
tions, strengthens the belief that all the granites and crystalline schists are 


pre-Cambrian. 


SHC TrON: ke 


GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 


After so much detail, it would seem only appropriate to convey the 
impressions I have gained as to the comparative genesis of the crystalline 
schists and allied granites. Considering as a whole the later series which 
I have referred to the Huronian, there can be no doubt that they were 
formed by the development of their various crystalline minerals out of 
preéxisting sediments, in such a mode that the chemistry of the original 
individual beds was unchanged. The same conclusion is doubtless true of 
the older series which are here assumed to be the equivalents of the Lau- 
rentian. 

Purely siliceous beds, either those composed of fine material or siliceous 
conglomerates, have retained their chemical simplicity even where highly 
basic beds, as of hornblendie gneiss, are interstratified with them. Had 
there been the slightest tendency toward chemical reaction between the ma- 
terials of adjoining beds, the highly basic layers would inevitably have com- 
bined with the contiguous quartz strata and developed minerals of resultant 
composition. On the other hand, the original forms of the clastic particles 
of which the beds were sedimented are entirely lost; the interstitial space 
which must necessarily have separated the irregular-shaped particles of 
detritus is totally obliterated, and the sole figure of the original sediment- 
ary particles is now shown in the pebbles of the conglomerates. 

In zones of simple material, like carbonate of lime or quartz, metamor- 
phism has been confined to an obliteration of interstitial space and crys- 
tallization. In beds originally of mixed mineral character, chemical affinity 
has resulted in the production of various new minerals, identical ultimate 
composition often failing to produce identical results; as, for instance, in 
the Huronian schists we find a bed in one place composed of quartz, ortho- 
clase, and biotite, while in another, the ultimate constitution remaining the 


same, are developed quartz, orthoclase, iron garnet, and muscovite. Fur- 
le 


GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 113 


ther, all metasomatic changes observed by us in the Huronian series are 
in like manner confined to individual heds. 

The presence of water, carbonic acid, and saturated solutions of salts 
at the time of crystallization is evidenced by the minute presence of these 
bodies as inclusions in several of the component minerals of the schists. 

It would seem, therefore, that we are authorized in assuming an approxi- 
mately complete knowledge of the chemical materials and their stratified con- 
dition at the time of crystallization. Pressure and heat being the only known 
exterior causes which could have codperated to induce the observed compres- 
sion, chemical combination, and crystallization, the vital question is as to their 
mode of action. Evidence of excessive heat seems to be wanting, at least of 
such temperature as could produce the slightest even local liquefaction, for the 
phenomena of groundmasses and bases which have in variably resulted from 
crystallization out of liquefied magmas, and which are thoroughly charac- 
teristic of known eruptive rocks, are altogether wanting among the schists ; 
so, too, the entire absence of glass inclusions in the component minerals is 
in a measure conclusive of the absence of molten or glassy passages during 
crystallization. The behavior and effect of great heat, however, are, as 
is well known, disturbed and rendered altogether abnormal by the presence 
of high pressure, as may be seen in the voleanic rocks, where the relative 
points of fusibility of various minerals, as determined at the earth’s sur- 
face, are not strictly held to in depth. One of the most common features 
in many of the rocks known to be eruptive is the envelopment by minerals 
of high fusibility of those of lower fusibility, and vice versa. 

If other forces can thus upset so apparently rigid a physical property 
as the temperature of fusibility, it is perhaps unsafe to argue from the 
absence of the products of fusion that a degree of heat adequate for lique- 
faction was absent while the crystalline schists were in process of formation. 
On the other hand, if post-Archean geology offers any analogy, it is, that in 
periods of metamorphism and the development of crystalline rocks, the crust 
has been subjected to the most severe pressure, and it would seem that press- 
ure, whether exerted downward by the building up of a superincumbent mass 
on terrestrial radii, or as developed in the tangential strains due to the earth’s 
shrinkage, has been at least the invariable accompaniment of diagenesis. 

8K 


114 SYSTEMATIC GEOLOGY. 


While thus theoretically, in the present stage of knowledge, it is impos- 
sible to assert that a temperature sufficient to liquefy was absent, it is quite 
safe to assume that either the temperature was below the degree necessary 
to melt any single ingredient, or else its effect was annulled by pressure, 
the fact being that in the formation of the schists there never was fusion, 
and that many minerals are present in a molecular condition which they 
are known never to retain if subjected to high temperature; Sheerer, in 
this connection, having shown the presence in granite of what he terms 
pyrognomic mineral species, namely, those which under high heat undergo 
a permanent molecular alteration, but which in granites and schists are in 
the unaltered state. Thus for all intents and purposes pressure becomes 
the dominant power in bringing about the condition necessary for the de- 
veloping of such chemical affinities as will produce the resultant minerals. 
A considerable degree of heat, with the presence of moisture and alkaline 
solution, was doubtless essential to the excitation of chemical affinity. 

In the development of the schists, what was the predominant pressure, 
and what the mode of action? For reasons which have been expressed 
before, I am undisturbed in the belief that the crystalline schists are sedi- 
ments spread out in the bed of the early Archzean ocean, for the most part 
mechanical, perhaps in some exceptional instances, such as the magnesian 
silicates, chemical precipitates as contended for by Hunt, or, as seems 
to me more probable, the results of mechanical separation by washing. I 
assume that they were the detritus of then existing land masses swept into 
the oceans and arranged in precisely the manner of subsequent aqueous 
formations. 

As beds of heterogeneous sediment, the heat to which they were sub- 
jected by conduction from the floor on which they were laid down could 
not have been sufficient, since it permitted the existence of oceans, to induce 
the chemically inert particles to break up their then existing combinations 
and begin a new chemical activity. It is only when subjected to enormous 
pressure from above or increased heat from below that the particles would 
be forced into new mineral combination. 

A simple inspection of the prominent crystalline schist and gneiss areas 


of western America shows, first, that as a whole they are among the thickest 


GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 115 


known bodies of conformable sediments. The geognostic behavior of subse- 
quent great bodies of conformable sediments may be profitably compared, and 
their dynamic laws applied to the ancient sediments of the Archean series. 

Post-Archzean sediments of detrital origin are well known to be 
thickest nearest the source of supply and to thin out over the more remote 
portions of the oceans. A section normal to a great sedimented coast region, 
as in the case of the Appalachian Paleeozoic series or the corresponding 
series in the Cordilleras of the Fortieth Parallel, shows a great accumulation 
near the ancient shores and a rapid thinning out toward the middle of the 
seas. It is difficult to suppose the conditions of deposition to have been 
otherwise for all detrital materials during Archzean time. 

A further law in the great conformable sediment of later time has been, 
that heavily loaded regions sink into the subjacent crust. This subsidence, 
as is evident from an inspection of sections, is a direct displacement of a 
part of the underlying floor and a gradual pressing downward of the accu- 
mulating sediments, by the weight of the continually piling up series. 

In the case of the conformable Paleozoic series, as exposed in the 
Wahsatch, where a section of 30,000 feet is displayed, it is evident that 
before disturbance, and while yet in the horizontal attitude of deposition, 
the lower Cambrian beds were under the pressure of a column of 30,000 feet 
of rock, that as marine sediments they were imbued with saline water, and 
that from mechanical compression and consequent loss of volume there 
must have been a considerable raising of temperature. 

A further increment of heat must have been caused by the inevitable 
rising of the earth’s concentric surfaces of temperature into the mass as it 
displaced crust and sank into the hotter depths of the earth. Yet with all 
this there is in the lowest Cambrian beds only the very slightest tendency to 
the production of crystalline schists. We have no reason to suppose that the 
thickness of Archzean conformable groups was enough greater than the 
series just cited to create a downward pressure so superior as by weight 
alone to bring about the totally dissimilar result of true schist crystallization. 

Between the two sets of conditions there was one radical difference, 
namely, the secular cooling of the earth and consequent secular recession 


of isothermal surfaces. 


116 SYSTEMATIC GEOLOGY. 


Supposing sedimentation, consequent subsidence of a series of beds, and 
the accompanying displacement of subjacent crust to take place in the same 
direct ratio of quantity now and in the earlier stages of the earth’s refriger- 
ation, given beds arriving at the same depth would in Archwan time find 
themselves raised to a temperature greater than at the same depth to-day, 
by the actual amount of secular recession of temperature through the whole 
vast interval of time. The Archean beds might easily find themselves, 
when pressed into the crust even to a moderate depth, in presence of those 
conditions essential for the processes of diagenesis. 

From all the well known synthetic studies of chemical combination 
under pressure, moderate heat, and alkaline solutions, it would seem that 
with a considerably hotter condition of the superficial crust of the globe the 
amount of subsidences known in post-Archean time might be sufficient to 
‘arry strata down into a region where chemical activity should begin. 

If this view of the probable history is correct, fair deductions are, first, 
that somewhere below the surface, varying with the thermal state of the 
earth, there will be a horizon with the necessary heat condition and re- 
quired superincumbent weight to urge the material present into chemical 
activity; secondly, that with the refrigeration of the globe this horizon will 
recede deeper and deeper toward the centre of the earth; thirdly, that so long 
as this horizon is within the depth to which bodies of sediment are brought by 
displacement of crust and subsidence, so long will crystalline schists continue 
to be made; fourthly, that when by secular. cooling the. required horizon 
passes below the possible levels to which strata may be sunk by displace- 
ment of crust due to accumulation of sediment, then forever afterward 
there will be no formation of the schists. Supposing no objection to be 
made to this hypothesis when applied to the gncisses, true schists, quartz- 
ites, marbles, dolomites, and chrysolites, there still remain to be accounted 
for the rocks characterized by the presence of hydrated protoxyd minerals 
and hydrous magnesian silicates. 

The view of Hunt that they were originally hydrous magnesian  sili- 
eates, of which an example is furnished by the sepiolite of the Paris Basin, 
is no longer tenable as regards most serpentines and chloritie rocks. Modern 


microscopic research has proved that these are direct pseudomorphs after 


GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. Gl 


anhydrous silicates, such as garnet and chrysolite, every stage of the whole 
process of pseudomorphism being shown beyond all doubt. Their origin is 
therefore relegated to the common origin of the anhydrous schists. The 
discovery in Appalachian schists of great bodies of chrysolitic formation, 
making an integral part of the crystalline schists, is sufficient answer to 
the question, Whence came the anhydrous magnesian silicate out of which 
to make the pseudomorphous serpentine ? 

Without attempting to examine the validity of Hunt’s claim that the 
early magnesian silicates are chemical precipitates from the acid ocean of 
their period, I see no reason to seek for a different origin for the magnesian 
silicates from that of the commoner aluminous minerals. Olivine-bearing 
rocks are among the oldest irruptive bodies ; why may not olivine sands, like 
those now seen on the shores of the Hawaiian Islands, have been then as now 
accumulated by the mechanical separation of sea currents and subsequently 
buried by rushes of feldspathic and quartz sands? Be that as it may, the 
whole tendency of microscopic research is to prove that the hydrous 
magnesian silicates are plainly pseudomorphic after anhydrous forms, and 
the problem of genesis, as Hunt very justly remarks in this connection, is, 
Whence the anhydrous ones? There is little present necessity, it seems to 
me, for the invocation of aqueous precipitates, when the sea bottom and 
shores of to-day offer such varied chemical materials which are so obviously 
detrital. 

From these considerations, so far as the gneisses and crystalline schists 
are concerned, I am led to give ina complete adhesion to the hypothesis of 
diagenesis for the anhydrous silicates and of subsequent pseudomorphism for 
the hydrous magnesian rocks. My views approximate closely to those of 
Dana, and, if I rightly comprehend him, of Gumbel, rejecting on the one 
hand the plutonic hypothesis of Naumann and his followers, and on the 
other the all but forgotten theory of direct crystallization from solution, as 
advanced by Delabeche. 


In the crystalline schists and gneisses are found identically the same 
anhydrous minerals which characterize the granites. The characteristic 
features of the schists are, the parallel-bedded arrangement, the strict reten- 


118 SYSTEMATIC GEOLOGY. 


tion of chemical materials in their original zones, and the interealation of 
beds made of simple materials like quartzites and limestones. Granite 
possesses the same minerals, and furthermore their microscopical structure 
and the character of their foreign inclusions are identical. The sole differ- 
ence seems to be, that granite is often demonstrably a plastic intrusion, and 
possesses no parallel arrangement of minerals, its various components lying 
more or less evenly distributed throughout the mass. In the granites and 
schists alike there is invariably a total absence of the phenomena of base, 
groundmass, and glass inclusions. The geognostic position of the schists is 
exactly like the other strata which were deposited horizontally and after- 
ward disturbed. On the other hand, granite, in an immense majority of 
cases, is found to be exposed either in the hearts of mountain ranges or in 
ridges which have been evidently subjected to immense orographical or 
tangential pressure. When the points of Archean mountain ranges pro- 
trude through gently inclined and subsequently unaltered strata, as is very 
often the case, the true orographical relations of the granite cannot be 
known. It is only when we can observe granite in direct connection with 
the strata into which it has intruded or out of which it has been made, that 
the true relations can be seen; and it is safe to say that wherever these 
intimate relations are observable, the granite occupies a region which has 
been subjected chiefly to horizontal or circumferential pressure. The fre- 
quent phenomena of the under-dip of the strata flanking a granite mass, as 
in the great granite body of the Sierra Nevada, are prominent instances of 
the intimate relation spoken of. If in such cases an unconformable over- 
lying and unaltered series were to cover all but the summits of the granite 
hills, the granite would appear simply as an unconformable underlying 
body, whose genetic relations are absolutely unknown. Into this category 
a vast number of granite exposures of the Cordilleras have to be placed. 

It is an invariable law, then, that where the genetic relations are clearly 
perceived, eruptive granite is always found in connection with very great 
horizontal pressure and consequent disturbance. Suppose, now, a deep- 
lying series of varied sedimentary beds, covered by sufficient superimposed 
mass to exert a pressure powerful enough to sink them to the necessary 


thermal horizon for the induction of crystallization in the material of the 


GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 119 


beds. As long as the attitude of these beds was undisturbed by horizontal 
compression, the result would be a series of crystalline schists and gneisses. 
But the moment horizontal or tangential pressure either overcame or disturbed 
the action of the downward pressure, the horizontal arrangement of these 
erystallizing materials would be broken up, and their resulting arrange- 
ment would depend upon the interaction of the two forces. In case the hori- 
zontal force were the slighter, the result would be simply those corrugated 
schists which are characteristic of certain regions. Butif the horizontal force 
suddenly or even gradually overcame the radial pressure of gravitation, the 
original arrangement of the strata would be broken up and their com- 
ponent beds crowded into a structureless mass. In that case the tougher 
and stronger minerals, and those whose crystalline forms were most compact, 
would suffer the least dislocation, while the long and slender bodies (or those 
whose crystalline nature developed easy cleavage or fracture) would be 
torn asunder, and the particles often widely distributed. Granite then would 
be made out of any sediments or rocky materials of the necessary chemical 
combination, carried down to the required thermal horizon, whenever tan- 
gential pressure overcame the effects of the downward thrust of a superin- 
cumbent mass. 

If this preéminently mechanical theory of granite be correct, we 
should find every gradation between the corrugated schists and gneisses 
and the uniform granites. Supposing the schist beds to be partially formed 
and in a more or less plastic condition, or even supposing them to be wholly 
crystalline when the horizontal pressure came to be exerted upon them, it is 
evident that if the breaking up of horizontal position which I have described 
took place, the beds would be ruptured and torn asunder, and that certain 
regions would be converted into a uniform granite, while others retained the 
traces of the original beds. Accordingly, we find in certain instances long 
tongue-like masses of crystalline schists mechanically entangled and em- 
bedded in structureless granite. The case already described in Wright’s 
Canon is a conspicuous example of this. A further stage of the obliteration 
of the original bedding would be found in the very great variations of a mass 
of granite where the materials had not been perfectly commingled, and 


accordingly in some great granite precipices the homogencous granite in- 


120 SYSTEMATIC GEOLOGY. 


cludes masses having the most extraordinarily irregular form, whose min- 
eralogical composition is totally different from that of the surrounding mass. 

There is not another such fine example of this in America as the wall 
of El Capitan, in the Yosemite Valley, which is a precipice 3,200 feet 
in height, the result of fracture, so smooth and so near the vertical 
plane that erosion has scarcely affected the fissure-surface. Upon the face, 
which in general is of a uniform gray granite, are seen irregular cloud-like 
masses and rudely lenticular bodies which seem to be made of segrega- 
tions of certain of the mineral components of the granite. The rock asa 
whole belongs to our fourth type, and is characterized by a high propor- 
tion of plagioclase, hornblende, and titanite. The irregular included bodies 
referred to are in some instances nearly black, and are made up of accumu- 
lations of brilliant black hornblende and quartz, absolutely without feldspar, 
and again with quartz in such low proportion that it may be said to be 
strictly a black amphibole rock, in which quartz is an accidental occurrence. 
Others of these segregations are of black mica and orthoclase, with a little 
quartz, to which the greatly predominating biotite gives a generally black 
appearance. Still others are of an aplitic type, being composed of ortho- 
clase and quartz. A study of this precipice would convince any observer 
that, whatever may have been the origin of the body as a whole, uniform 
commingling has failed to take place, and that the sharply defined inclu- 
sions are mechanical, not chemical, accidents. 

Suppose erosion to lay bare a horizontal face of this rock on which 
should be observed at intervals these various included bodies. A field ob- 
server, coming upon them and finding their boundaries very sharply de- 
fined by the enclosing granite, would naturally suppose them to be intrusive 
masses of different nature, and they would be mapped according to their 
wineralogical composition. Whereas in this magnificent Capitan section, 
which lets us into the nature of these deep-lying masses, it is seen that they 
are mere local dependences of the granite, and they may be regarded as 
enveloped bodies which for some reason or other have resisted the tendency 
to become merged in the main granite. 

Were the chief factor in the genesis of granite to be, as I suppose, 
tangential, or, as I like to denominate it, orographical pressure, there must 


GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. Pall 


of necessity be all the transitions from a uniform homogeneous granite down 
to those rocks in which radial or gravitation pressure has produced the 
ordinary bedded schists; and it would seem that such envelopments as 
are seen upon the front of El Capitan, and also in a less conspicuous 
way in many of the granites of the Fortieth Parallel, might be considered 
parts of the original beds, which the accidents of pressure have failed to 
commingle into a general mass of uniform granite. 

Finally, this distinction between the action of the forces of gravity and 
those of tangential compression, as accounting for the characteristic differ- 
ences between bedded schists and mineralogically identical but structureless 
granite, is offered, not as a rounded theory, but as an hypothesis which to 
the mind of the writer best accounts for the present known facts. 


SECTION LY. 
PRE-CAMBRIAN TOPOGRAPHY. 


After the consideration of the mode of occurrence of the Archzean 
bodies and their petrological correlations, there remains a further and still 
more interesting feature of the Archean age, namely, the configuration 
and general relief of the area of the Fortieth Parallel at the close of 
Archean time and prior to the deposition of the unconformably overly- 
ing Cambrian beds. I am aided in this interesting enquiry by the relations 
of the Palsozoic, which, as already repeatedly said, are observed to be 
conformable from the lowest members of the Cambrian to the top of the 
Upper Coal Measures. Over the whole distance from the Rocky Mountains 
to western Nevada, in almost every prominent range, the contact may be 
observed between the Archzean and the Palzeozoic series. At times Archzean 
summits are seen to rise above the level of the deposition of the Upper 
Carboniferous, and the contact is exposed at various points all the way 
from that horizon down to the lowest exposures of the Cambrian, an extreme 
range of over 30,000 feet. It is obvious, therefore, that in any single 
mountain range the exposure of a contact between the Archzean and the 
Palaeozoic, covering a given number of feet in thickness of Palzozoic strata, 
represents just that much actual topographical slope of Archean hills. 
Assuming the deposit-plane of the Upper Coal Measures to have represented 
a uniform level, this level, closing as it does the great conformable Palzeo- 
zoic series, forms a datum-surface from which the features of Archean 
topography may be worked out. 

Over the Rocky Mountain system as exposed from Rawlings’ Peak 
to the east base of Colorado Range, the entire Paleeozoic series, from 
the Cambrian to the Upper Coal Measures inclusive, is not over 1,000 
feet in total thickness. Passing westward from this region, a maximum 
thickness of 32,000 feet is reached in the Wahsatch. In other words, the 
Paleozoic has thickened from 1,U00 to 32,000 feet between the meridians 
of 105° and 112°. Now, if the plane of deposition of the uppermost mem- 


122 


PRE.CAMBRIAN TOPOGRAPHY. 123 


ber of the Palsozoic had represented throughout an actual level, the differ- 
ence of depths of the ocean in which the Paleozoic sediments were laid 
down would probably be equal to the increase in the thickness of the series. 
But from all that may be observed of the present mode of deposition in 
ocean basins, as well as the data obtained from the study of extended 
exposures of the earlier rocks, it is in no wise probable that a given geolog- 
ical horizon necessarily represents a level plane of deposition. On the con- 
trary, over an ocean of greatly varying bottom it would seem that there 
must of necessity be some tendency on the part of deposited beds to follow 
the larger depressions of the bottom. The proximity of shores and the 
force of currents must of necessity greatly vary this law; but it should be 
at the same time recognized that there is a constant tendency to approach 
a level. It is true that the Cambrian formation as displayed on the Fortieth 
Parallel has been very unevenly deposited, and has shown a general ten- 
dency to fill up the lowest depression with enormously thick accumulations 
of detrital material. I leave out of consideration the continued deepening 
of the Palzeozoic ocean bottom, because, although important im an orograph- 
ical sense, it does not bear upon the question of detailed topography of the 
ocean bed, the only enquiry here pursued. Rising in the Paleozoic series, 
a horizon of deposition would represent constantly a nearer approximation 
to the level; so that at the close of the series it is not at all improbable 
that the Upper Coal Measures showed no very great deviations from a gen- 
eral plane. 

In assuming the top of the Paleozoic as a plane from which to work 
out the forms of the Archean bottom, it is true that we arrive at mimimum 
results of the depth of the ocean; we simply obtain the depth of deposit 
below a fixed surface. The Palzeozoic series represents the material accu- 
mulated in the bottom of the pre-Triassic ocean, and gives no clew to the 
real ocean surface of the period. In consequence, the Archaan topography 
represents only that which was buried under the bottom of the Paleozoic 
ocean, and leaves us entirely in the dark as to the heights to which the con- 
tinental and insular bodies rose either above the plane of deposition or above 
the actual surface of the ocean. When, therefore, I assign to the Archean 
mountain peaks a height of 30,000 feet, it is obvious that there is to be 


124 SYSTEMATIC GEOLOGY. 


added to this a certain unknown quantity which will give them a still more 
imposing height. 

Some vague ideas of the additional altitude of the land masses of the 
Archean above the plane of deposition may be obtained in the Rocky 
Mountains and in the country west of Reese River. It is clear that in the 
case of Park Range there are at present 5,000 feet lifted above the horizon 
of the Carboniferous contact. This is demonstrated by the overlap of the 
Trias and Jura, which are shown along the flanks of the range. To this 
5,000 feet must be added the elevation which has been removed by 
erosion—an element that cannot have been unimportant. So, too, west 
of Battle Mountain, in western Nevada, Archzean land rose above the limits 
of deposition of the Carboniferous and formed a broad area extending 
westward into California, over which no Carboniferous has been deposited. 
Within Nevada there is no evidence that this was in general more than a 
land mass of moderately rolling topography; and, as will be seen in a later 
chapter, its area and extent must remain entirely problematical. A few 
known points were lifted fully 6,000 feet above the lower regions. 

From the westernmost exposures of the Palaeozoic, it is evident that 
the series has lost none of its thickness in passing westward from the Wah- 
satch. On the contrary, those members whose limits are clearly defined in 
western Nevada are even thicker than in the Wahsatch. It is natural that 
there against the shore of the continent of Pacifis, the area directly deliver- 
ing its detrital material to the ocean which covered America, all sediments 
should be at their maximum; but that they should retain a thickness of 82,000 
feet as far east as the Wahsatch, 300 miles from the continent which mainly 
furnished them, is most surprising. The special configuration of this broad 
ocean bottom was diversified by enormous mountain ranges, far exceeding 
in height the elevations of modern chains. The greatest single mountain 
slopes now exposed in the Fortieth Parallel territory are those in Colorado 
Range, where the extreme peaks are lifted 9,000 feet above the Great Plains. 
The highest known slope of the old Archean peaks is shown in the Cotton- 
wood Cafions of the Wahsatch, where a single, highly inclined, almost 
precipitous face of 30,000 feet was presented to the west—a mountain 
wall far exceeding that of any known modern example. At Red Creek, on 


PRE-CAMBRIAN TOPOGRAPHY. 125 


the north base of the Uinta Mountains, the contact between the Uinta sand- 
stones and the old quartzitic Archeean mountain shows a nearly vertical 
precipice of not less than 10,000 feet, with some actually overhanging 
cliffs. Besides these observable and measurable slopes there must have been 
a considerable amount removed from high summits by erosion, and we have 
no means of knowing whether the lowest exposure of the Cambrian really 
represents the base of the series, or whether there may be a still further 
addition to reach what was the true base of the great Archaean peaks. In 
the northern part of the Wahsatch the topography was that of broad dome- 
like peaks with more gently inclined sides; yet their average elevation 
must have been very great, since they touch the Silurian and Devonian 
level, and we know the Cambrian to have been at least 15,000 feet thick. 
The height of this range above its base must therefore have been from 
17,000+ feet to 30,000+ feet. In a later chapter will be discussed the 
influence of these immense underlying ranges upon subsequent mountain 
folds, and it is expected to show that they have entirely controlled the 
subsequent topographical features. 

At the bottom of the map of the Archean exposures, at the close of this 
chapter, is drawn a section representing the various members of the Paleo- 
zoic series, starting in the region of the Rocky Mountains at the west base 
of Park Range, where the whole Palaozoic does not exceed 1,000 feet, 
and thickening westward to the region of the Wahsatch, where it reaches 
nearly its greatest expansion. It will be seen that Park Range is given an 
elevation of 5,000 or 6,000 feet above the level of the Carboniferous, that 
being its present proven height above the point of Carboniferous contact. 
In the region of Red Creek is shown the great Archean peak, whose out- 
crop appears upon the map on the north base of the Uinta. Unfortunately 
the precipitous face of 10,000 feet is turned toward the south, so that it 
cannot be shown in an east-and-west section. In this region the outlines 
given in the section are entirely hypothetical, and are based upon the indi- 
cations of the east-and-west slope as given at the points of contact between 
the Archean and the Weber quartzite. Between Park Range and Red Creek 
there is no Archzean exposure, and the configuration of the bottom is there- 


fore not known. So too between Red Creek and the Wahsatch it is quite 


126 SYSTEMATIC GEOLOGY. 


unknown. At the Wahsatch is given the immense mass, having its culmi- 
nation in Clayton’s Peak, which rises nearly to the top of the Weber quartz- 
ite and sweeps downward to the west beneath the 15,000 feet of conform- 
able Cambrian. Westward the Archzean masses of Wachoe, Humboldt, and 
Cortez ranges are seen rising to their proper elevations, as shown by the 
local sections observed in the field; while between these different mountains 
are (leep valleys whose bottom strata are afterward upheaved into interme- 
diate ranges, as for example in Pinon Range, between the Cortez and Hum- 
boldt Archzean bodies; and finally to the west of Battle Mountain is shown 
the sweeping up of Archzean land above the level of the Paleozoic series, 
forming a barrier in that direction. West of the Pinon the lower Cambrian 
is entirely unobserved, no section penetrating deeply enough in the moun- 
tain cores to expose it. There is no evidence, however, that it may not 
exist, under the exposed strata of the Pinon, or anywhere between the 
Wahsatch and the western limits of the Paleozoic, as thick or even thicker 
than the Wahsatch development. 

While, therefore, there is much in this section that is hypothetical, there 
are still many fixed quantities, such as the great slope at Red Creek, the 
enormous precipice at the Wahsatch, the towering peaks of the Cortez as 
lifted above the lower strata of the Pinon, and the depth of Cambrian as 
shown in the ranges of the desert west of Salt Lake. We are amply war- 
ranted in assuming the heights thus given for the Archaan mountain bodies, 
and it is further evident that while much of their elevation is due to origi- 
nally eroded surfaces, the great mountain wall in the Wahsatch, and also 
that at Red Creek, can only be the result of faults. It is impossible to 
suppose a precipice of Archzean schists like that exposed at Red Creek to 
be the result of other than absolute fracture. Therefore upon the Archzean 
bottom of the ocean in which the Paleozoic strata were deposited, there 
were mountain ranges of magnificent proportions, whose flexed beds and 
faulted precipices show all the orographical phenomena known to modern 
ranges. ‘Their great importance consists not only in their being features of 


i 


the Archeean surface, but in the fact that in them is found the local cause 
of modern ranges, and that in their nature and origin, as well as in that 
of subsequent uplifts, is to be studied the deeper and primal cause of moun- 


tain building. 


AW 


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EmSOZOIC EXPOSURES 


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CHAPTER III. 
PALHOZOIC. 


SECTION L—PALZOZOIC EXPOSURES.—PROVINCE OF THE ROCKY MOUNTAINS—UINTA 
RANGE—WAHSATCH RANGE—PROVINCE OF GREAT BASIN—CAMBRIAN AND 
SILURIAN—OGDEN QUARTZITE—WAHSATCH LIMESTONE—WEBER QUARTZ- 
ITE—UPPER COAL MEASURES. 

SEcTION II.—RECAPITULATION OF PAL0ZOIC SERIES. 


Si CyL WO Nar: 
PALHOZOIC EXPOSURES. 


Province oF THE Rocky Movunrarins.—In Colorado Range, between 
Colorado Springs and latitude 41°, the lowest sedimentary rocks found in 
contact with the metamorphic Archzean series are sandstones of the Triassic 
age. The appearance of the Paleozoic series near Colorado Springs has 
been described by Hayden. Directly south of the 41st parallel, on the 
eastern foot-hills of the range, in the neighborhood of the head waters of 
Box Elder Creek, limestones of the Paleozoic begin to appear, and from 
there northward to the northern limits of our map they are found in contact 
with the Archzean series, save in a few places where horizontal strata of the 
Niobrara and Wyoming conglomerate Tertiaries advance eastward and cover 
the entire upturned sedimentary series. Conspicuous instances of this over- 
lap of the Tertiaries masking the Paleozoic are noticeable directly north of 
Granite Canon Station on the railway, at the head waters of the Chugwater, 
and again at Sybille and Bush creeks. With these exceptions there is a con- 
tinuous chain of Palzeozoic outcrops from the head waters of Box Elder 
Creek for seventy miles northward. As shown upon Map L., the strike of 


127 


128 SYSTEMATIC GEOLOGY. 


this exposure is exceedingly sinuous and follows the protrusions and reén- 
trant curves of the Archean. Tast-and-west it varies in width from a quarter 
of a mile.to four miles, and in dip from the low angle of 15° or 16°, at the 
head of Box Elder Creek, up to the vertical, and in some instances at the 
extreme north to a reverse dip. On the west side of the range the first ap- 
pearance of the Paleozoic coming out from beneath the overlap of the con- 
formable Trias may be seen directly north of Harney Station. Thence to 
the northernmost limit of the map it is a broad, continuous belt from six to 
ten miles wide, dipping gently to the west. The Paleozoic series upon 
the east side of the range dip invariably to the east. South of the Union 
Pacific Railroad on the west side of the range, and south of the head waters 
of Box Elder Creek on the east side of the range, red Triassic sandstones 
lie directly in contact with the Archean series. In consideration of the op- 
posing dips of the sedimentary rocks on both sides of the range, it is at once 
evident that the whole northern part of the range has been simply a broad 
anticlinal thrown into a steep dip on the eastern side, and that erosion has 
carried off nearly the entire sedimentary series, leaving only margins of 
upturned beds, all the axial portion having been removed. North of the 
41st parallel, undoubtedly the entire series, down to the Cambrian, ex- 
tended quite across. South of that latitude it is evident, from the over- 
lap of the Triassic, that the Paleozoic series were not deposited over the 
whole present area of the range In other words, the southern Archeean 
region was formerly, as now, much higher than the Laramie Hills, and while 
the Paleozoic was deposited conformably over the top of the Laramie Hills 
the southern edges of its members abutted against the elevated slopes of a 
lofty Archzean island. Even the Laramie Hills were undoubtedly a ridge 
prior to the deposition of the Paleozoic series; and it is therefore natural 
that over a submerged ridge having a plateau-summit the superficial cur- 
rents of the ocean should have made themselves felt, and the consequent 
deposition be slight. As a result, the entire Paleozoic series is limited to 
a total thickness of 859 feet. Upon Map I. of the Atlas, as well as 
upon Analytical Map IL, at the close of this chapter, it will be seen that 
the Paleeozoie series at this locality is designated by but one color, without 


the subdivisions which appear to the west, and that this color is the same 


PALMOZOIC EXPOSURES. 129 


as is elsewhere given to the Upper Coal Measures; the reason being that 
this horizon is the only one which has been definitely determined by pala- 
ontological evidence. Certainly the upper 700 of the 850 feet are found to 
contain fossils directly referable to the Upper Coal Measure series, and in 
the scanty exposure below that horizon, within the limits of our work, we 
have failed to detect any organic remains. The lower 150 feet consist of 
red limestones and a reddish sandstone of varying fineness. Farther north, 
in the Black Hills, Dr. Hayden, Prof. N. H. Winchell, and the late Mr. 
Newton obtained a large number of Primordial types from a zone cor- 
responding precisely with the red limestone and red sandstone which under- 
Jie our Coal Measure limestone. The equivalence of section is carried out 
by the constant finding in the Black Hills of Coal Measure fossils close 
above the Primordial zone. These two members of the Paleozoic series 
may be traced southward into the region of our map, and so far as strati- 
graphical and lithological proofs are worth anything they tend to show that 
the red siliceous zone underlying the limestones of the Laramie Hills is 
simply a continuation of the Primordial sandstone of the Black Hills. 
Although we have actually found no fossils in this horizon, we feel the 
greatest confidence in asserting that the whole Palwozoic series, from the 
Primordial to the Triassic, is here compressed within the 850 feet. The 
following local section from the base upward, from examinations at the 
table between Horse and Lodge Pole creeks, presents a characteristic aver- 
age result : 


Feet. 
1. Compact, fine, gray sandstone, almost a quartzite, with thin sheets 
On conelOMerate:— 5 tka Peat ors Sarees Se cir ees Sok 100 
Zehcadisn=wiite SANGStOnGss tra tase .c clcist Ae eut- Soe oe ec crcic ss 50 
Jorlved. aronaceouss lmmMOstOnen=.- eatin ccs 5.012 «scree ae cerns Soe 50 
4. Gray and blue arenaceous limestone, 
5. Thin bed of conglomerate, 
6. Binishlimestone, highly siliceous, bse wine ee eee = 650 
7. Pink and cream-colored limestone, alter- 
nating with thin sandy beds, 
Movil 2 pret cep al les ANE eS eg 2 len ce a eo 850 


130 SYSTEMATIC GEOLOGY. 


At Granite Cation, just north of the Union Pacific Railroad, the follow- 
ing section, also counted from the base upward, was obtained : 


1. Compact, reddish-gray sandstones with fine pebbles. 
2. Brilliant red arenaceous limestones. 

3. Massive blue limestones. 

4. Light-gray limestone, with arenaceous beds. 


East of Signal Peak, three or four miles south of the railroad, the sec- 
tion gave: 


Feet. 
1. Red sandstone, with considerable variety of texture, calcareous 
near the topis2% 2asicwa ne tne a eee 100 
2, ,bluish-pray limestone... a: sick te 2B ee oo ere eee 400 
3. Red arenaceous limestone, 
4, chinsbed of fine .conglomerate,\- sso ssh 2c. aes ome eee 300 
5. Blue limestone, J 
A Noy?) ee eee en Mee Dar cometary Seka y en tok 800 


Throughout the series there is a noticeable absence of slates, clays, 
marls, and mud rocks. The sandstones are all more or less calcareous, and 
throughout the limestone strata there are passages which are gritty, or 
more or less finely siliceous. Within the heavily bedded limestones are fre- 
quently intercalated narrow zones of pure sandstone, with or without the addi- 
tion of fine conglomerates. The lower and presumably Cambrian sandstones 
are subject to great local variations of color and texture. They are some- 
times so hard and compact as closely to approach quartzite, and again produce 
coarse and friable conglomerates made up of more or less rolled Archean 
pebbles and a fine, gritty, siliceous matrix. They are almost everywhere 
of a prevailing reddish color, and are always calcareous toward the top, 
passing by a variety of gradations—in some places abrupt, in others by 
gradual intercalation—into a red arenaceous limestone which itself presents 
a close superficial resemblance to certain red quartzites. In the finer sili- 
ceous material and in the red arenaceous limestones there is not infrequently 
a fine banding of color, indicating a variation of sediment; but the rock 
shows no disposition to split upon the color bands. The body of Paleozoic 


PALAOZOIC EXPOSURES. il 


limestone varies greatly, both in purity and in physical condition. Toward 
the bottom, and indeed through by far the greater part of its thickness, it is 
a dull, dark limestone, interrupted by coarsely arenaceous beds. The gen- 
eral colors are dark bluish-gray, with pink and white saccharoidal and 
granular beds near the upper limits of the series. Between given hori- 
zons, with their gentle westerly dip on the west side of the range, and in a 
nearly vertical position along the eastern foot-hills, there is the greatest 
physical difference, the nearly horizontal beds showing but little alteration, 
the more highly inclined being variably altered into hard, compact strata, 
the beds of exceptional pureness becoming a coarse white marble. The 
darker and lower beds of the series are largely dolomitic. A fragment from 
this locality, submitted to chemical analysis by Mr. B. E. Brewster, is 
recorded in the table of limestone analyses given in the general résumé of 
sedimentary geology. 

The very uppermost beds directly underlying the red Triassic sand- 
stone at Horse Creek are of very fine-grained limestone of a deep flesh-red 
color, with small sparkling crystals of calcite disseminated through it. It 
is in general characteristic of the whole upper zone of limestone, and under 
analysis proves to be nearly a pure dolomite, containing— 


Carbonaterofelimers at 928222220. ool oe. 60. 09 
Carbonate of magnesia.--..-....-.......2.. 2. 39. 20 
otal sane ese The 99. 29 


The impurities are small grains of silica. Under the microscope the 
fine red zone of limestone which serves to divide the Cambrian sandstones 
from the dark-gray limestone is seen to be a mixture of red, siliceous grains, 
which are usually quite sharply angular, and minute crystals of calcite. 
The only fossils obtained from this series are characteristic of the Coal 
Measures, namely : 

Productus semireticulatus. 
Productus cora. 
Productus prattenianus. 
Athyris subtilita. 


BY} SYSTEMATIC GEOLOGY. 


Mr. G. B. Grinnell* mentions the discovery of a Spirifera centronata 
in the Black Hill beds, but he does not say in what part of the limestone 
it occurred. Farther westward, in the belt of the Fortieth Parallel Explo- 
ration, this fossil is found to be characteristic of the Waverly group in 
what we have denominated the Wahsatch limestone, occurring in numerous 
localities in Wahsatch and Oquirrh ranges. If, as is probably the case, this 
fossil occurs in the lowermost beds in the Black Hills, it will be interesting 
as marking another of the horizons which have developed in great thick- 
ness to the west, but are here compressed into such narrow limits. It 
may be predicted that sooner or later the missing horizons between the 

Trias and the Cambrian are likely to be in large part discovered, for in 
“an ocean in which undisturbed deposition took place from the beginning 
of the Cambrian to the close of the Mesozoic age no great period of time 
would be likely to elapse without sedimentation, and it is to be predicted 
that one after another the now missing main horizons will be identified, 
even if reduced to extreme thinness. 

After this general statement, a few local details will serve to fix the 
main phenomena of the Paleeozoic occurrence in this region. South of the 
head of Richaud Creek, on the east side of the range, the limestones of the 
Paleozoic series strike about north-and-south, dipping 70° to 75° to the east. 
North of Richaud Creek their strike is north 40° east, with a dip of about 
60° to the southeast. In other words, the upturned edge of the Paleozoic 
exposure follows the topography of the massive Archean spurs. This is 
especially noticeable near the head of the Chugwater, where the Paleozoic 
and with it the conformable Mesozoic series, from the supposed Cambrian to 
the top of the Colorado group of the Cretaceous, wraps around a southwardly 
projecting Archzean spur and sweeps northward, following the curve of a 
recntrant angle, and then strikes south again along the flanks of Iron Moun- 
tain, describing between the head of Richaud Creek and the head of the 
south fork of the Chugwater a complete letter §. As a result of this 
extreme sinuosity of strike, the limestones are considerably altered, and on 
the tops of the ridges frequently develop a fair variety of white marble. 
From a short distance south of Iron Mountain a sheet of Pliocene con- 


* Black Hills of Dakota, Ludlow, 1874. 


PALAOZOIC EXPOSURES. 133 


glomerates overlaps the whole upturned stratified series, and abuts against 
the Archean; but south of Shelter Bluffs the bold limestones of the Palexo- 
zoic again come to the surface, and thence southward to the south fork of 
Crow Creek they form the dominant feature of the foot-hills. From the 
north fork of Horse Creek to Wahlbach Springs the Paleozoic limestones rise 
above the top of the overlying Triassic beds to a height of 500 or 600 feet, 
exposing sheer cliffs of Carboniferous limestones standing at an angle of 
70°. This ridge is intersected by three streams, which divide it into sharp, 
wave-like blocks trending a little west of north. The limestone here con- 
tains numerous fossils, of which Productus semireticulatus was the only 
determinable species. Just north of Wahlbach Springs the Paleozoic 
declines to an easterly dip of 15° or 20°. South of that point, between 
the Cheyenne Pass road and the north branch of Crow Creek, it extends 
out from the main Archean range some distance eastward, and falls off to 
the east in a nearly perpendicular, precipitous front of 700 or 800 feet. 
It is also abrupt to the west, where it is separated from the main Ar- 
chxean region by a sharp canon. ‘The Paleozoic series here forms a nearly 
horizontal table. From its position it seems to suggest a connection with 
the gently dipping limestones of the west side of the range. It is, indeed, 
evident that over the entire plateau-like summit of this region the western 
dipping members of the anticlinal once extended in a nearly horizontal 
position. In that view it would be more correct to describe the orographi- 
cal structure as a sharp monoclinal break with a scarcely perceptible dip 
to the west and a very deep plunge to the east. The rocks of this Table 
Mountain are really in the position of a shallow synclinal, the western 
edge dipping slightly to the east and the eastern edge slightly to the west. 
It is interesting as the sole instance where any but Archean rocks appear 
between the two foot-hill belts of Paleozoic rocks. West of Wahlbach 
Springs the Palwozoic has an exceedingly gentle dip, approaching the hori- 
zontal position which once obtained over the whole plateau-summit of the 
ridge. Sharp, wave-like ridges recur just south of the north branch of Crow 
Creek, and form interesting outlines, showing the grayish-white limestone, 
which is nearly always the upper member of the Paleeozoic series here. On 


the north side of the south branch of Crow Creek a nearly vertical position 
) 


134 SYSTEMATIC GEOLOGY. 


is maintained by the Paleozoic series, which is here quite thin. The lower 
members are probably entirely wanting; the upper ones overlap into uncon- 
formable contact with the Archean, the lowest exposed beds consisting of a 
compact conglomerate, not unlike one which is interstratified far up in the 
limestone, as seen at various points on the western slope. Directly north of 
the Union Pacific Railroad the Carboniferous again forms an outlying ridge 
composed in its upper members of the gray limestones underlaid by the 
characteristic red sandstone. The whole strike is a few degrees west of 
north, with an eastward dip of from 30° to 35°. The basal red sandstone, 
capped by red arenaceous limestone, is very well developed, and is overlaid 
by massive blue limestones, which are again succeeded by the lighter and 
more fossiliferous series. South of the railway line the Paleozoic declines 
to a dip of only 30° to the east, and in the very middle of the belt are 
obtained abundant Productus cora and Athyris subtilita. Still farther south- 
ward the rocks decline to 8° and 10° easterly dip, and continue in an un- 
broken outcrop as far as the old Denver and Laramie stage-road. It will 
thus be seen that an extremely high general dip, only locally varied by 
shallow angles, and great sinuosities of strike, dominated by the rigid spurs 
and reéntrant curves of the Archzean, are the characteristics of the chain 
of Paleozoic outcrops on the east side of Colorado Range. 

Along the west flank, as already mentioned, the series makes a continu- 
ous outcrop from the northern limit of the map to a point two miles north 
of the Pacific Railroad, where it is overlapped by the conformable red 
Trias. Throughout this distance the Paleozoic series rests unconformably 
upon the Archean and maintains a comparatively uniform position, free 
from all noticeable local flexures, varying in dip from 5° to 6° west, and 
reaching an extreme inclination of 12°. Always next to the Archean 
series occur the red sandstones, which we correlate with the Black Hills 
Primordial, presenting toward the east a rather abrupt, but low, mural 
outcrop. Lithologically, the Primordial coincides with that already de- 
scribed upon the east side, appearing chiefly as a coarse red sandstone, 
more or less compact, made up of a matrix of fine quartz-grains containing 
angular pebbles, and in places passing into an indurated conglomerate. 


None of the beds display the quartzitie tendency seen in the steeply dip- 


PALAHOZOIC EXPOSURES. foo 


ping basal beds of the east flank of the range. So, too, the marbleized 
passages of limestone are wanting in this gently dipping western series. 
The lower sandstones pass up into granular, variably arenaceous, reddish- 
yellow limestones. Hither from originally greater thickness, or from less 
compression, the series here is developed about 1,200 feet thick. On the 
western side no fossils were obtained from the uppermost members, but 
distinct Coal Measure types were obtained within 200 feet of the base. 
Where the road which traverses the range from the Sybille descends the west 
flank and crosses the zone of Palseozoic, which here dips from 5° to 7° to 
the west, the bluish-gray limestones, forming a zone of 250 or 300 feet, 
and reaching down to within 200 feet of the base of the series, yield the fol- 
lowing determinable species : 


Productus prattenianus. 
Productus costatus. 
Athyris subtilita. 


Near the top of Cheyenne Pass, also, in a very similar limestone, doubt- 
less indicating the same horizon, were found— 


Productus semireticulatus. 
Productus cora. 

Athyris subtilita. 
Bellerophon, sp.? 
Orthoceras, sp.? 


Northwest of Sherman are seen excellent exposures of the base of the 
series. Here the lower red sandstone is characteristically, though thinly, 
developed, and is seen to be succeeded above by a grayish limestone with a 
red tinge, the whole striking north 20° east, and dipping 7° to 9° west. 
Near the base of the limestone, and but slightly removed from the so-called 
Cambrian sandstone, were obtained — 

Productus prattenianus. 


Productus cora. 


In Medicine Bow Range a locally exposed fragment of the Palo- 
zoic makes its appearance where Laramie River leaves the mountains. 


136 SYSTEMATIC GEOLOGY. 


Directly resting upon the Archean is a body of light-blue Carboniferous 
limestone standing nearly vertical, and covered to the north and south by 
the overlapping sandstones of the Trias. Nine or ten miles to the north, 
into the Cretaceous basin, projects a powerful promontory of Archsean 
rocks, culminating in Bellevue Peak. Around the northern end of this 
promontory, about 1,000 feet above the plain, is wrapped a semicircular 
outerop of Paleozoic rocks, dipping from 20° to 25° to the north. Although 
predominantly of limestone, the exposure is saccharoidal in texture and 
highly arenaceous throughout. 

On the west side of Medicine Bow Range, and immediately north of 
the 40th parallel, in North Park, the Triassic sandstones, which generally 
form the lowest exposed member of the stratified series, resting directly 
and unconformably upon the Archean, are eroded off, uncovering a local 
exposure of Carboniferous limestones, for the most part bluish-gray, locally 
varied by arenaceous zones. They yielded no fossils, but clearly belong 
to the upper portion of the Coal Measure series. 

At Elk Mountain, the extreme northwest point of Medicine Bow Range, 
the conditions described at Bellevue Peak and at the head of the Chug- 
water are repeated. Around a bold Archzean boss, which rises above the 
Tertiary and Cretaceous of the plains, is wrapped a belt of the Palaeozoic 
limestones, which extend up to within 1,200 or 1,500 feet of the summit of 
the peak. As usual where the lower sedimentary series is bent around an 
Archean body, the overlying conformable rocks, up as far as the Colorado 
group, partake of the flexure. Here the limestones possess a coarsely 
crystalline texture, and many of the beds are highly arenaceous. At the 
same time they are not so characteristically bedded as the limestones of the 
same horizon on the Laramie Hills. At Sheep Butte, where the beds dip 
80°, the arenaceous condition of the limestone may be clearly seen, and 
among the beds are pure bluish-gray sandstones. 

At Rawlings Peak a mass of Archean has been thrust up, carrying 
with it a full section of the Palzeozoic and Mesozoic series, and erosion has 
cut into the heart of this local dome, displaying admirable sections from the 
Laramie group of the Cretaceous down through the whole series to the 


Archeean. Immediately overlying the gneisses appeared the siliceous strata 


PALHOZOIC EXPOSURES. 137 


already noted as underlying the Carboniferous limestones. The greatest 
thickness exposed cannot be less than 700 feet of gray and white quartzites 
and sandstones, which have something of a reddish tinge upon their 
weathered surfaces, the individual beds usually not exceeding one or two 
feet in thickness. At the bottom is a fine-grained conglomerate about seventy 
feet thick, consisting of small white quartz pebbles in a finely siliceous 
matrix. The uppermost bed is a ferruginous sandstone fifteen feet thick. 
No fossils were obtained, except indistinct fucoidal remains. Conformably 
over this series is a deposit of almost chemically normal red hematite. 
Where seen, it is about twenty feet thick. It is already of considerable 
commercial value, having been mined as a paint and flux. Directly over- 
lying the ferruginous zone is a bed of limestone about fifty feet thick, so 
compact and fine-grained as to resemble some of the lithographic limestones 
of our Jurassic series. South of the railroad at Rawlings Gap, the same 
lithographic limestone is seen, overlaid by darker, heavier limestone beds, 
the whole dipping 10° southward. Farther north, about two miles from 
the railroad, the best sections are obtained. Ilere, however, a thickness of 
only about 150 feet of quartzitic series is exposed in the valley. This is di- 
rectly overlaid by the ferruginous sandstones, and above that the fifty feet. 
of drab lithographic limestones, darker toward the base, followed above by 
about thirty feet of white siliceous limestone, and this by beds of varying 
thickness of dark-blue earthy limestone, from which were obtained Pleuro- 
phorus oblongus and some fragments of a strongly curved Productus. Above 
the blue fossiliferous limestone is a dark earthy bluish limestone, sometimes 
shaded with red, followed by forty feet more of grayish granular limestone, 
making thus far 200 feet of lime series, which are here succeeded by fifty 
feet of arenaceous shales, beyond which is a gap of 500 feet, through whose 
earthy surface outcrop occasional edges of thin arenaceous shales. From 
the character of the soil, this gap is assumed to be largely made up of unseen 
calcareous and argillaceous beds. Above this is another gap, without out- 
crop, of 400 feet, limited above by the distinct and characteristic Triassic 
beds Directly under the latter is a fine-grained, semicrystalline drab 
limestone, in which was found Natica lelia, a new species occurring also 
along the East Fork of the Du Chesne, on the south side of the Uinta 


138 SYSTEMATIC GEOLOGY. 


Mountains, where it is associated with distinctly Permo-Carboniferous fos- 
sils, and, as here, its horizon is directly succeeded by the lower members 
of the Trias. In view of the occurrences in the Wahsatch and Uinta, the 
evidence that this Natica bed represents the top of the Permian is consid- 
ered clear. Therefore the upper portion of the 1,150 feet of beds included 
between the Primordial quartzites and the Triassic sandstone is colored and 
considered as Permo-Carboniferous. 

From a reference to Analytical Map IL., exhibiting the Paleeozoic ex- 
posures, it will be seen that in the country already treated in this chapter— 
namely, the region of the Rocky Mountains proper, shown inMap I. of the 
Atlas 


ical history of the region, form but an insignificant portion of the total 


the Paleozoic exposures, though an important link in the geolog- 


area. They are altogether confined to immediate contact with the Archzean 
masses, and in all cases dip directly from them. The maximum thick- 
ness of the whole Palaeozoic series, as exposed along Colorado Range, is 
1,200 feet. At the Rawlings uplift the series is expanded both at the top 
and bottom—upward, by the appearance of Permo-Carboniferous strata 
between the Upper Coal Measure horizon and the Trias sandstones, down- 
ward by the expansion of the Primordial or Cambrian member of the series, 
which here reaches 700 feet in thickness. The only fossils obtained belong 
to the horizon of the Coal Measures, with the exception of the single Natica 
which marks the Permo-Carboniferous. Although they are barren of fos- 
sils, from the downward sequence of beds, we have no doubt whatever 
that the red sandstones, conglomerates, and quartzites underlying the Car- 
boniferous limestones belong, as we have correlated them, with the Primor- 
dial of the Black Hills and Colorado Range. On the east side of Laramie 
Hills the Paleozoic series reaches its greatest compression, namely, to 800 
feet in thickness. There is absolutely no unconformity from the base to 
the summit. Therefore in this thin deposit is represented all the time from 
the Cambrian to the Trias, and yet organic life is only represented by types 
of the Coal Measure epoch and the Permian. This is perhaps natural, as 
fully three fifths of the whole series carries these fossils, for here, as farther 
to the west, the Coal Measure age furnished by far the greater amount of 
sediment. Yet it is not a little peculiar that representatives of the sub- 


PALMOZOIC EXPOSURES. 139 


Carboniferous, Devonian, Silurian, and Cambrian ages should not be even 
hinted at. The stratigraphical correlation with fossiliferous horizons a few 
miles north of our area is so evidently natural that our assignment of hori- 
zon may, I think, be safely relied on. 

Uinta Rancr.—In leaving the Rocky Mountains and passing into the 
basin of Green River, the Palseozoic series manifest themselves in much 
ereater thickness and far greater individualization of horizons. Another 
characteristic difference is to be noted between the region already described 
and that of the Uinta. In the former, the Paleozoic outcrops are simply 
bands of upturned strata edges bordering massive ranges of Archean rock. 
In the region of the Uinta they are absolute folded uplifts of Paleozoic 
material, laid bare by the removal of the entire Mesozoic series which were 
upheaved with and formerly overarched them. In the Rocky Mountains 
the thin Palzeozoic was deposited around Archean islands and over Ar- 
cheean plateaus. When the two came to be uplifted together, erosion easily 
removed parts of the Paleozoic covering, laying bare the older series. 
In the Uinta region the vast scale of Paleozoic deposits, with propor- 
tionally great conformable Mesozoic beds, makes the later folds of such 
great thickness that erosion has been powerless to remove material farther 
down than the Middle Carboniferous. There is only a single instance 
where the Archzean is reached, and that is the case of a great isolated schist 
peak around which the Upper Carboniferous was deposited. 

Uinta Range is a broad, plateau-like anticlinal, whose summit re- 
gion has scarcely a perceptible dip, while the flanks, both by curvature 
and dislocation, are thrown into every variety of contorted and highly 
inclined position. The other Palzeozoic exposures of this region are two 
isolated masses of Carboniferous which form really the eastern extension 
of the Uinta and represent the dying out of the mountain building action 
in that direction. Aside from these, which belong to the system of the 
Uinta, there is a considerable exposure of Upper Coal Measure limestones 
bordering Bear River near the northern extremity of Map III. of the geo- 
logical series, and this is essentially a part of the Wahsatch system. The 
Palzeozoic exposures of the Green River Basin, considered as a province, 


or in comparison with those of the Rocky Mountain region, would never 


140 SYSTEMATIC GEOLOGY. 


have been altogether intelligible or clearly correlated with those to the west 
but for the key-section which unravels the relations of the whole series, a 
section exposed and repeated upon three lines in Wahsatch Range; and 
since, in these middle longitudes of our work, the series as a whole has 
reached such a great thickness and such remarkable stratigraphical indi- 
vidualization, hereafter it will be best later to treat the various divisions of 
the Palzeozoic, both stratigraphic and historic, by themselves. 

The Uinta system forms one of the exceedingly limited number of 
exceptions in the parts of the Cordillera system to a general northerly 
trend, the average strike of topographical axes being within 30° or 40° of 
the meridian. There is a considerable number of ranges having an accu- 
rately meridional trend; others north 40° east; others north 50° west; 
but of ranges following a parallel of latitude there are very few. The 
Siskiyou, near the northern boundary of California, the eruptive out- 
bursts of Arizona and western New Mexico, and the system of the Uinta, 
form the chief examples of direct east-and-west lines of upheaval. The 
range is formed of an anticlinal having a broad plateau-summit often 
twenty miles from north to south, the strata of this upland region resting 
in a nearly horizontal position. At the north and south, along two dis- 
tinctly marked lines of sudden flexure, the rocks dip away from this central 
plateau of level strata. The region of abrupt change from the approxi- 
mately horizontal position to the steep northern and southern dips, is marked 
by tremendous local faults and every variety of lateral and longitudinal 
compression. The Paleozoic rocks of the range consist prominently of 
three members : 

1. An immense body of quartzites and indurated sandstones interca- 
lated with groups of sheets of argillaceous shale, the whole forming the 
lowest of the Uinta Palaeozoic series, and referred by us (not, however, 
without some questioning) to the Weber quartzite or middle member of the 
Coal Measures. The general thickness is 12,000 feet. 

2. Directly overlying this throughout the whole range is observed 
a series of sandstones and limestones, more or less variable, and having a 
thickness of 2,000 to 2,500 feet. From the base to the summit of this 
series Coal Measure fossils are obtained. 


PALHOZOIC EXPOSURES. 141 


3. Overlying the uppermost member of the Coal Measure limestones, 
but exposed at only a few localities, is a body of calcareous and argilla- 
ceous shales and mud rocks, bearing typical Permo-Carboniferous fossils. 

These features obtain throughout the length of the Uinta as far east as 
the meridian of 109° 20’. I will now note certain characteristic exposures 
of the Upper Coal Measures. 

Overlying the quartzites of O-wi-yu-kuts plateau, east of the head of 
Willow Creek, were found hills of drab Upper Coal Measure limestone, 
which dip about 50° to the north. We are unable to detect any noncon- 
formity between this series and the quartzites below at this point. South- 
east of Diamond Mountain extends a sharp ridge, forming the eastern edge 
of O-wi-yu-kuts, in which is exposed the whole series of the Upper Coal 
Measure sandstones and limestones, having a strike of 17° north of west 
and a dip of 31° to the northeast. Between the Coal Measure limestone 
and the underlying sandstones was again observed a true conformity. 

East of that the simple structure is complicated by a series of broad 
crumplings on the south-and-east terminus of the range, where evidence of 
a north-and-south folding is observed, and the two outlying masses of Palaeo- 
zoic which rise above the Tertiary are local quaquaversal uplifts, having 
their longer axis drawn north-and-south. These two outlying bodies, Yaim- 
pa Peak and Junction Peak, are each chiefly made up of the mixed arena- 
ceous limestones and calcareous sand rocks, which, taken together, form the 
group of Upper Coal Measure strata; and in the summits of both masses, 
owing chiefly to faults, a portion of the underlying quartzite is brought to 
light. The local structure of these outlying bodies will be found fully de- 
scribed in Volume II. 

The outcrops of the Upper Coal Measure limestones along the north- 
ern flank of the Uinta trace an irregular line, as may be seen by Map II. 
of the Atlas, or by Analytical Map II. at the end of this chapter. They 
produce a series of wave-like ridges, either continuous or separated by 
the narrow canons of streams, forming a distinct noticeable ridge traced 
parallel to the strike of the range. As is the case with all these outlying 
Coal Measure limestone ridges, both here and along the Rocky Mountains, 
they present an escarped face toward the range, while the backs of the 


142 SYSTEMATIO*GEOLOGY. 


strata dip outwardly toward the valleys. At the head of Black’s Fork, 
beneath the red Trias, are good exposures of the soft Permo-Carboniferous 
and Upper Coal Measure beds. In the region of Gilbert's Meadows the 
Tertiaries overlap the Upper Coal Measure series and come directly in con- 
tact with the lower quartzitic mass. Farther west, however, at Lime Pass, 
the Tertiary beds are eroded away, exposing the limestones of the Coal 
Measures, which dip 45° to the northeast and strike 15° north of east. The 
strata best exposed are gray and blue limestones, which rise in bold, wave- 
like ridges, the overlying clayey beds having been largely worn away in 
low saddles and ravines or covered up by débris. Still farther to the 
west, opposite Lime Pass, the softer Permian beds are seen to consist of 
mud rocks and slates closely corresponding to the similar series of rocks 
between the Upper Coal Measure and Trias sandstones in Weber Canon of 
the Wahsatch. From the Carboniferous limestones here were obtained a few 
fossils, Productus prattenianus being the chief recognizable form. The upper 
member of the Coal Measure series here consists of conglomerates which are 
very coarse west of Lime Pass. To the east, however, the lowest member 
seems to be a coarse-grained gray sandstone, a gritty siliceous matrix con- 
taining grains of limpid quartz, somewhat tinged with iron oxyd. At the 
head of Burnt Fork the characteristic steep wave-ridges, geologically below 
the red Triassic sandstones, are of the limestones of the Coal Measures, still 
preserving a strike of about 15° south of east and a dip of from 35° to 45° 
to the north. 

This series again outcrops in Vermilion Creek Cajon, a cut 1,500 feet 
deep, yielding an excellent section of the Upper Coal Measure series, dip- 
ping 27° to the northeast. Beginning at the top of this section, from 100 
to 150 feet of variable cherty limestone are exposed, from which were 
obtained — 

Fusilina sp.? 

Nucula parva. 

Nucula sp.? (minute forms in limestone). 
Pleurotomaria (casts in limestone). 
Bellerophon carbonaria (very abundant). 


PALAOZOIC EXPOSURES. 143 


Beneath these is a thickness of about 900 feet of light buff and gray 
sandstones, thinly bedded and variably calcareous. Farther west this 
sandstone member becomes altogether calcareous, and, indeed, through- 
out the region of the Uinta it may be considered either a calcifer- 
ous sandstone or a siliceous limestone, according to its local variations. 
More essentially limy toward the base, it finally gives way to a soft 
series of mixed buff and gray sandstones intercalated with limestones. 
Below the buff intercalated sandstones and limestones, which may possibly 
be 1,100 feet in thickness, is a bed about 100 feet thick of very noticeable 
pinkish sandstone, and below this 500 to 600 feet of mixed drab sand- 
stones and limestones. In the upper mixed sandstones and limestones are 
several noticeable cherty seams, none, however, to be compared with the 
thick cherty limestone which caps the series; and in the intercalated zone 
below the upper cherty limestone are also seen several black seams three 
or four inches thick, highly ferruginous. One of the fine-grained cherts 
of the lower group, subjected to analysis, yielded — 


DUNC Ge as age oe a a Nee I eM 8 96.5 
Carnonaterom limoe- 26. ee kis sec lace eee es 2.0 
Carbonatevof magnesia ...-2....-225..22-42------ 0.7 
iirongandralumingd W882 oa ot nee ce oats eta eae 0.6 
VNIcLLO tee eee eens sea Steeda are es Siavere ee eee rae) owes 0.4 


The prominent capping cherty limestone is quite constant wherever in the 
Uinta a good section of the whole Coal Measure series is obtained, and it 
is to be considered as the dividing line between this group and the Permo- 
Carboniferous. It is curious to observe that where the Upper Carbonif- 
erous series is exposed in a canon section like this, the siliceous members 
seem to predominate. If, on the other hand, the section is exposed upon a 
ridge, calcareous members predominate in the outcrop and in the débris. 
This is evidently due to the greater brittleness and easy fracture of the 
sandstones. But careful sections of this series display remarkable varia- 
tions over very small geographical areas. 

Directly and conformably above the cherty Bellerophon-bearing beds at 
Vermilion Creek there is a series of several hundred feet of greenish clays 


144 SYSTEMATIC GEOLOGY. 


and mud rocks, giving evidence of moderately shallow water deposit, and 
clearly representing the Permo-Carboniferous 

Overlying the heavy red sandstones of the Weber series, as displayed 
upon the summit of the Escalante Hills, isa great development of the Upper 
Carboniferous rocks, extending southward until it passes under the Mesozoic 
beds which form the divide between Yampa and White rivers. Here is an 
extent of country about sixteen miles from north to south by thirty-five miles 
from east to west—with the slight exception of overlying masses of Triassic, 
mere fragments left in the general erosion—composed of intercalated sand- 
stones and limestones of the Upper Coal Measure series. The interesting 
orographic phenomena of this region will be found detailed in their proper 
chapter. Yampa Canon itself is cut through the members of this series, the 
abrupt walls of the gorge showing a fine section of the mixed sandstones and 
limestones which belong directly under the cherty Bellerophon limestones and 
extend down into the drab limestones and sandstones that overlie the red 
Weber sandstones. Toward the western limits of Yampa Plateau several 
interesting sections are displayed. That of Section Ridge presents a sharp 
anticlinal, with axis northeast-and-southwest, sinking abruptly to the south- 
west. The ridge is capped by limestones which belong to the horizon of 
the cherty Bellerophon series, though the strata here are less siliceous than 
at Vermilion Creek. They dip 20° to the northwest, approximately with 
the slope of the hill, forming an abrupt escarpment to the southeast. The 
upper members contain — 


Nuculana bellistriata. 
Schicodus curtus. 
Orthis carbonaria. 
Orthoceras crebrosum. 
Naiadites. 


Fossils representing the upper part of the drab limestone and sandstone 
group which constitutes the lower members of the Upper Carboniferous 
series are found about twelve miles southeast of Zenobia Peak: 

Spirifer lineatus. 

Spirifer opimus. 


. 


“sy 


Vi 


4 


PALZOZOIC EXPOSURES. 145 


A considerable number of undeterminable forms are also found. These 
fossils seem to correspond with the horizon in the region of the pink sand- 
stones of Vermilion Creek. The exposures of Yampa Canon show very 
heavily bedded rocks, as indeed do almost all exposures of horizontal rocks in 
vertical canons. The lower part of the canon section shows a prevailing red 
color not unlike the deep-pink beds of Vermilion Creek Canon. 

West of the great canon of Lodore the Upper Coal Measure series ex- 
poses a line of bluffs which form the southern wall of Summit Valley, cul- 
minating in Ute Peak. Here the upper beds of the Weber sandstones are 
coarse-grained red rocks of glistening surface and loose texture, broken by 
frosts into large massive blocks with rounded edges. Conformably overly- 
ing this sandstone is a bed of reddish, decomposed limestone, containing 
many partially decomposed calc-spar forms, some of which are circular, as 
if they had been the casts of corals. The limestone is exceedingly siliceous, 
containing 28 per cent. of quartz sand and 70 per cent. of carbonate of lime. 
Above this are about fifty feet of coarse white sandstone, over which lie 
limestone shales and a dense, compact, heavily bedded blue limestone, 
with conchoidal fracture, rich in fossils. The following forms were 
identified : 

Spiriferina Kentuckensis. 
Athyris subtilita. 
Meekella striocostata. 


These are the lowest forms obtained from the Upper Coal Measure sys- 
tem in the Uinta, and are collected within sixty feet of heavy beds of the 
Weber. The beds at this point dip about 15° a little west of south. To the 
west of Ute Peak, in limestones occupying a higher position and inter- 
calated in sandy shales, were found fragments of Syringopora. 

Geode Canon offers in its deep, picturesque gorge a section of the 
Upper Coal Measure and Lower Mesozoic series 2,000 feet deep. The 
upper portion is cut through nearly horizontal beds of the Upper Coal 
Measures, while near the mouth of the canon the beds round over to a 
dip of 29° to the south. The Bellerophon cherts are easily recognized, and 
contain the usual casts of Orthoceras and two species of Bellerophon, besides 
Bellerophon carbonaria, together with a specifically unrecognizable Discina. 

10 K 


146 SYSTEMATIC GEOLOGY. 


This bed is here about fifty feet thick, underlaid by fifty feet more of yel- 
low, compact, cherty limestone, abounding in geodes lined with cale-spar 
crystals and concretions of flint. Beneath it is a seam of thin, compact 
sand and clay, rich in oxyd of iron. Below are massive beds of compact 
white sandstone, variably calciferous, and passing downward into intereal- 
ated sandstones and limestones. 

Directly under the red Triassic sandstones of the foot-hills of the East 
Fork of the Du Chesne, for a considerable distance, the formation is com- 
posed of thinly bedded mud rocks, fine shaly limestones, and calcareous, 
argillaceous shales, yielding the following species: 


Myalina (resembling sub-quadratica.) 

Myalina n. sp. 

Bakevellia parva. 

Pleurophorus sp.? 

Macrodon sp.? 
These are the only fossils obtained in Uinta Range from the soft, easily 
eroded beds that separate the lower sandstones of the Trias from the 
Bellerophon cherts which mark the uppermost horizon of the Coal Measures, 
and are interesting since the forms as well as the physical condition of the 
beds are closely allied to the Permo-Carboniferous of Weber Canon. 

Along Rhodes’s Spur, which rises west of the Du Chesne Canon, the 

drab limestones near the base of the Upper Coal Measure series appear with 
the shallow dip of the upper plateau. From the base of the formation, not 
far above the Weber beds, were obtained — 

Chonetes granulifera. 

Martinia lineata. 

Syringopora multattenuata. 

Zaphrentis. 

Lathostrotion. 

Euomphaltus. 

Half-way from Kamas Prairie down to Provo Valley, the trachytes 

are sufficiently eroded to display a limited outcrop of grayish-blue lime- 
stones having a dip to the south and west. These extend for half a mile 


PALMHOZOIC EXPOSURES. 147 


along the bank of the stream, overlaid by a red sandstone, probably 
Triassic, none of which, however, was found in place. It was identified by 
débris protruding through the soil. This is interesting as indicating the 
wrapping of the Upper Coal Measures around the western end of the Uinta 
uplift. Where the upper Weber Catton emerges from the Uinta Mountains 
a body of drab limestone is seen, forming the southern wall of the cation, 
and having a dip of 25° to the northwest. From the foot-hills of the range, 
near Kamas Prairie, were obtained, at a point evidently not far removed 
from the contact with the Weber formation — 


Productus semireticulatus. 

Spiriferina pulchra. 

Martinia lineata. 
So far as we have observed, there is no nonconformity here between the 
limestones and the underlying quartzites. 

Along the northern flanks of the Uinta Mountains, over their western 
extent, indeed west of Lime Pass, the exposures of the Upper Coal Measures 
are usually covered either with Tertiary or modern débris, and owing to 
the dense growth of forest, outcrops are obscure and rare. Enough is seen, 
however, to trace the continuity and arrive at the structural outline of the 
series, but not enough to throw light upon the lithological variation or to 
add to the fauna. 

As may be seen from a glance at the map, the Upper Coal Measure 
series, whose features have just been treated, remain in the form of a band 
of variable thickness, surrounding the central anticlinal plateau, but never 
arching continuously across, except at the extreme eastern and western ends. 
In other words, from the entire central portion of the uplift erosion has 
removed not only the overlying Mesozoic but the Upper Carboniferous, 
exposing the sandstone and quartzite formation of the Weber for a width 
north-and-south varying from twelve to twenty-five miles, with an extreme 
length from east to west of about 150 miles, the trend showing a slight con- 
vex curve to the north. The main central mass rises in a comparatively 
horizontal position, showing a slight anticlinal curvature in transverse direc- 


tion, which is complicated by faultings at the north and south extremities, 


148 SYSTEMATIC GEOLOGY. 


and sags which appear in transverse section at various points of the arch; 
and when viewed longitudinally the axis itself is seen not to represent an 
even line, but a series of shallow sags and arches. The result is a compli- 
cated system of undulations, whose dips rarely exceed 5° to 8°, while 
along the northern edge the immense series of strata is flexed sharply over 
to the north in positions which vary from a slight dip to 55°, the flexure 
being accompanied and followed by extensive dislocations. There is thus 
displayed a thickness which we estimate at 12,000 feet, although the canon 
section, as determined by Major Powell,* exceeds that amount. The best 
and deepest exposures are those offered by the O-wi-yu-kuts Plateau, the 
Canon of Lodore, the head of Black’s Fork, and the head of Bear River. 
Plate V. shows the walls of the Canon of Lodore, where the steep preci- 
pices of horizontal Weber beds are about 3,000 feet high. 

The axial region of Weber sandstones in the region of Brown’s Park 
has been both dislocated and deeply eroded, permitting the Tertiary Val- 
ley of Brown’s Park to occupy the interval between two elevated moun- 
tainous plateaus of the Weber sandstone. On O-wi-yu-kuts itself the Weber 
formation is seen to rest unconformably against the eroded surface of the 
Red Creek Archzean body. Along its northern edge it dips with apparent 
conformity under the Upper Coal Measure series | Southward and through 
the main body of O-wi-yu-kuts Plateau the sandstones approach a nearly 
horizontal position. On the cliffs overlooking Brown’s Park, at the canon 
of Beaver Creek, for instance, they dip 5° to the north. These cliffs 
bordering the northern side of Brown’s Park rise rapidly about 1,800 feet, 
displaying the edges of the series) They are usually formed of a red, 
indurated sandstone tending to quartzite, and along their southern margin, 
especially toward the eastern opening of Brown’s Park, the lower beds 
bend over into a southern inclination, the extreme examples dipping 8° to 
the south. Following northward, the beds curve over into a position of 
from 50° to 60° to the north. The relation of the less steeply dipping 
but geologically superior Upper Coal Measure series of Diamond Creek 
is considered to be explained by the downthrow of the gently inclined 
limestone strata into contact with the underlying sandstones. An appar- 


* Geology of the Uinta Mountains, 1876. 


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PALASOZOIC EXPOSURES. 149 


ent nonconformity here, in a region of evident dislocation, has no bearing 
upon the actual conformity of the two series. Minor dislocations in the 
O-wi-yu-kuts sandstones themselves suggest caution in estimating the thick- 
ness of the beds. As estimated by us, there are exposed here about 10,000 
feet of the Weber series, for the most part of heavily bedded, rusty yel- 
low or red, sometimes grayish, compact sandstones, with limited passages 
of actual quartzite. The general color of the exposure, either in the 
canons or upon the bold wails fronting Brown’s Park, is a dark, earthy, 
purplish red. The surface of the eastern end of O-wi-yu-kuts Plateau is 
seen to be ribbed by the edges of the gently inclined sandstone strata, 
which have a strike much more east-and-west than the overlying Carbon- 
iferous series to the east. These parallel ribbed outcrops of the sandstone 
series extend up close under the limestone cliffs, whose beds at first glance 
would seem to have been deposited unconformably over their edges. But 
this apparent nonconformity is explained by a curved fault of the over- 
lying series. West of the west end of the Archaan mass of Red Creek, the 
sandstones of the Weber group have a dip generally from 10° to 15° to the 
north. North of Ashley Park, however, the beds are seen to have been de- 
posited unconformably upon the Archzean body. The planes of contact are 
shown on the hills west of Garnet Canon, in a little stream which is indi- 
cated on Map IL. by a dotted line near the western edge of the Archzean 
body, and also eastward in Willow Creek, where a distinct nonconform- 
ity is seen between the two series. Several prominent conglomerate sheets 
start from what was formerly the Archean shore; and as displayed by the 
heights east of Willow Creek, it is evident that the deposition of the Weber 
series not only extended to the summit of the Red Creek body, but actually 
overtopped it by a considerable thickness. Plate VI. shows the deeply 
eroded canons of Green and Yampa rivers at their junction, one of the 
most interesting instances of canon-cutting. 

Beneath the Coal Measures which are exposed near Lime Pass, on the 
narrow ridge at the head of Black’s Fork and Bear River, a great thickness 
of the Weber group is exposed. From Lime Point southward into the 
range, the dip increases from 45° to 52°, without displaying the slightest 


nonconformity, while up near the summit of the ridge it bends over to 


150 SYSTEMATIC GEOLOGY. 


nearly 16°, beyond which, in the axes of the flexure, there is a sudden 
break, involving dislocation, the rocks at the head of the canon in the Bear 
River region dipping 4° to 5° to the south, and showing a slight dip also to 
the east and west, which indicates that that region is one of the longitudinal 
axial arches. As here displayed, the upper beds are chiefly of a coarse, 
gritty, red sandstone, not infrequently banded like the colored jaspers. Be- 
low this is an immense mass of red and purplish quartzitic sandstones, 
sometimes so coarse as to constitute a conglomerate, and containing a 
varying admixture of but slightly decomposed, shattered crystals of ortho- 
clase and plagioclase. Greenish clay shale beds from 50 to 100 feet thick, 
sometimes hardened into green argillaceous slates, which in extreme cases 
of alteration contain a little mica, alternate with the quartzitic sandstones. 
In descending the series, the rocks become more compact, with frequent white 
opaque beds, to which the name sandstone is no longer applicable; they are 
essentially rough quartzites. Not less than 10,000 feet of conformable mem- 
bers of the Weber series, from the highest beds displayed at Lime Point to 
the lowest white quartzites, are here exposed, and to these must be added an 
unknown amount extending indefinitely under the horizontal central region. 

At Tokewanna Peak the beds have a dip of 16° to the north. There 
is an exposure of a great amount of red quartzites on the ridge to the south 
of the peak. Here the northern axis of the range is well defined in a break 
beyond the second point south of this peak, above which the beds have a 
dip of 6° to the south. 

Above the morainal material of Gilbert’s Meadows the first expos- 
ures are Weber quartzite beds dipping 42° to the north. This angle holds 
in ascending the creek to the forks, where it flattens out on the sides to 
a dip of 20° for about two miles, and then near a side ravine changes 
suddenly to horizontal, and farther up dips 5° to the south. An evi- 
dent fault has taken place here, separating the horizontal interior sum- 
mit region from the northern inclined beds. On the northern side of Gil- 
bert’s Peak the quartzites dip 42° to the north, while the beds which form 
the peak itself are of sandstone, with a slight southern dip, and include 
several strata of bluish clay beds about 100 feet in thickness. These are 
entirely wanting in the upper 1,000 feet of the peak. South of this the 


PALAOZOIC EXPOSURES. 151 


quartzites have a dip of 3° to 5° to the south, and the axis of flexure is seen 
to have here a northeast direction from Tokewanna Ridge to this point, 
bending still more to the north at Smith’s Fork, while to the east it curves 
into an east-and-west trend. The northern shoulders of the main ridge to 
the east of Gilbert’s Peak have a dip of from 3° to 5° to the north. North- 
ward it rapidly curves over into the steep dip of the limestone, which it 
conformably underlies. 

An important point, as showing the relations between the Weber and 
the overlying Upper Carboniferous, is at the eastern apex of the Uinta fold, 
near Little Snake River, where in a small conical hill northeast of the gap 
the heavy beds of the Weber are found, conformably overlaid by the 
lower drab limestones of the Upper Carboniferous series dipping 45° north- 
east, with a strike of north 50° west. So, too, at East Mountain the north 
face is composed of the southerly dipping beds of the Weber formation, 
conformably overlaid by the Upper Carboniferous drab limestones. 

The geological conditions of the southern slope of the Uinta differ from 
the northern edge simply in the greater gradualness of the flexure and the 
comparative absence of considerable faults. At Mount Lena the glistening 
red sandstones which form the uppermost member of the Weber dip 7° to 
10° to the south, and pass conformably under the drab limestones of the 
Upper Coal Measures. West of the Three Lakes, and near the head of 
Ute Fork, are seen heavy exposures of the striped red quartzite, which is 
one of the upper members of the Weber group. It here dips to the south 
from 7° to 9°, and carries some of the thick clay beds which were men- 
tioned at Gilbert's Peak. Above the mouth of a creek which descends 
the southern slope from Emmons’ Peak the uppermost members of the 
Weber quartzite are again exposed. They are here of heavily bedded 
sandstone, striped purple and red, while in ascending the range or 
descending the geological series the rocks become more quartzitic and 
of lighter color. In both the upper cations of the Du Chesne is well 
shown the quartzite series which here have a gentle dip to the south, 
exposing walls, more or less obscured by débris and forest, 2,000 or 3,000 
feet in height. 


In general, the summit region, although formed of approximately 


ay SYSTEMATIC GEOLOGY. 


horizontal strata, is deeply carved by glacial action into the characteristic 
amphitheatres formerly occupied by the névés—amphitheatres which de- 
liver their drainage into deep J canons formerly occupied by trunk gla- 
ciers, whose walls are from 2,000 to 3,000 feet in height. Plate VII., a view 
in the lower valley of the Middle Fork of Bear River, shows the broad gla- 
cier cafion with glimpses of the quartzitic mountains, although not of 
summit peaks. The horizontality of these beds gives to the precipitous 
faces of the spurs and amphitheatre walls the look of a gigantic masonry 
laid up in even courses. A typical summit region is that of Mount Agassiz. 
The peak itself is formed of coarse quartzitic sandstone containing rounded 
pebbles, beneath which is a zone of rough grits 800 or 900 feet thick, carry- 
ing quartz pebbles up to the size of a hazel-nut. The general color of 
the zone is pale green. Under this is a reddish-brown rock containing 
pebbles and beds of slate and shaly sandstone. The intercalated mud and 
shale beds are scarcely altered; they closely resemble the soft mud strata of 
the Connecticut River sandstone. Interstratified with the white quartzites 
in the bottom of the Agassiz amphitheatre, are a few sheets, never over 
three or four feet in thickness, which contain a little finely comminuted 
white mica, which was probably developed here, not preserved as original 
sedimentary particles. 

Upon the slopes of Mount Agassiz, about 1,000 or 1,500 feet below 
the summit, in a piece of quartzitic débris which could not be distinguished 
from the rock iz situ immediately above it, was obtained half of a ribbed 
brachiopod, referred with some doubt by Hall and Whitfield to Spirifer imbrez. 
The material of the fossil itself is precisely that of the enclosing quartzite, 
and there is a strong probability that the fragment represents a horizon 
about 700 feet down from the summit of Mount Agassiz, and the fossil, 
which is a Carboniferous one, offers very fair evidence of the age of 
the series. It is altogether impossible that a fragment of the limestones 
which once arched over this region could have withstood the long period 
of erosion which has degraded the range since the close of the Cretaceous 
age. I therefore conclude that this cannot be a relic of the fossiliferous 
Upper Coal Measures which were once vertically above the spot. It seems 
equally improbable that a traveller, Indian or otherwise, should have acci- 


ry 


Co 


ial 


wip 3 


-PALAHOZOIC EXPOSURES. | 153 


dentally dropped on this débris pile a foreign fragment identical with the 
neighboring rock in place. 

From another portion of the upper Bear River Valley, and on another 
débris pile, was also obtained a quartz pebble containing the impression 
of a crinoid column. While I admit the possibility of these being acci- 
dentally imported fragments, the presumption is decidedly in favor of their 
belonging to the quartzites of the region; and until better evidence to the 
contrary is adduced, I consider that they must be held to have indicated a 
Coal Measure age for the series. How well this coincides with the evidence 
of the Wahsatch section, will be shown hereafter. 

Plate VIII. shows Mount Agassiz at the head of Bear River, as seen 
over a lake which occupies a deep glacial basin excavated in the horizontal 
Weber beds. 

In the bottom of the basin, directly under Mount Agassiz, are heavy 
beds of white feldspar-bearing quartzite, deeply intersected by a variety 
of planes, jointing the rock into rough blocks. Plate IX. is a near, 
detailed view of the level tabular quartzite of Mount Agassiz. In these 
white quartzites are sheets of conglomerates consisting of rounded peb- 
bles of pure white quartz and of a red jaspery material, with one or two 
evidently of crystalline schist containing the material of a dioritoid gneiss. 
Intercalated in these beds of quartzite is a series of muddy shales which 
easily weather out, leaving deep chambers between the strata of quartzite. 
The summit rocks dip about 8° to the south. Those to the north incline 
from 5° to 7° northward. A specimen of the whiter quartzite gave upon 
analysis 98.5 of silica, the remaining constituents being lime and alumina. 

Northward the canon of Bear River descends more rapidly than the in- 
clination of the strata for five or six miles, when the beds are suddenly broken 
and flexed over into a dip of 45° to the north. In the comparatively hori- 
zontal summit series are exposed from 4,000 to 5,000 feet of southerly dip- 
ping beds, about an equal amount dipping to the north. 

In conclusion, the Uinta Palzeozoic series consists of — 

1. A series of siliceous beds 12,000-+ feet thick, impure sandstones at the 
east end of the uplift, but gradually compacted into quartzite in the western 
portion of the range; these beds are intercalated with groups of clay shales 


154 SYSTEMATIC GEOLOGY. 


and occasional conglomerate -sheets which contain round rolled Archean 
pebbles. 

2. Conformably, as we believe, over No. 1 is a series 2,000 to 2,500 feet 
thick of mixed limestone, calciferous sandstones, and cherty limestones, 
showing great variability in the thickness of bedding, but prevailingly of 
heavy limestone near the base, with varying thin-bedded intercalations of 
lime and sand near the top, always capped with a zone of highly cherty 
Bellerophon-hearing limestones. From bottom to top the series is rich in 
Upper Coal Measure fossils. 

3. From 200 to 500 feet of caleareous shales and argillaceous rocks 
and clays, intervening between the Coal Measures and Trias, conformable 
to both, and carrying Permo-Carboniferous fossils. 


Wanusatcn Rance.—This, far the most remarkable geological occurrence 
of stratified rocks in the American Cordilleras, derives its chief interest from 
the continuous exposure of a conformable Palzeozoic series, 30,600 feet in 
thickness, extending from the top of the Permo-Carboniferous down through 
the whole series consecutively, and ending 12,000 feet below the uppermost 
horizon of the Primordial. Not the least remarkable of the features of this 
Paleeozoic display is the manner in which these enormously thick series 
are wrapped around nucleal bodies of Archzean which represent the 
mountain slopes of a pre-Cambrian ridge. 

The range within the limits of our Exploration, as shown upon Atlas- 
Map IIL., is naturally divided into three portions: First, the great semicir- 
cular sweep of strata around the Archean and granitic centre of Lone 
Peak. Second, a similar mass curving around the Archzean body which 
occupies the summit of the range from a few miles north of Salt Lake 
City to the region of Ogden. Third, the northward projection of the 
strata from that point, which is depressed beneath the horizontal Tertiaries 
in latitude 41° 45’. The dip of all these exposures is to the east, north, 
and south—never to the west. An immense axial fault has cleft down the 
centre of the range from north to south, and the western half has been de- 
pressed and its rocks buried beneath the Pliocene and Quaternary exposures 
of Salt Lake Valley. The range therefore represents half of a great fold 
which has suffered much longitudinal compression and been faulted down 


PLATE VII 


U.S. Geol. Exp]. 40 Parallel 


“AVION AHONVY VINTON ~ ZISSVOV 


LW 


(INV 


THT 


AMV 'T 


EAE AOF ane SRSAS Sah 


~~ 


+ 


a 
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ou 


+ 


PALMOZOIC EXPOSURES. 155 


the axis. The interesting orographic details of this structure will be found 
fully described in Chapter III, of Volume IL., and their essential features 
again treated in Chapter VIII. of this volume. 

A full description of the Paleozoic outcrops of this range would 
occupy more space than has been allotted to the whole of this volume, and 
I must content myself with a sufficient number of the great characteristic 
exposures to constitute a proof of their correlation into a generalized see- 
tion. In order that these sections may be better understood, I offer here 
a mere outlined statement of the chief beds, in the order of their super- 
position. Beginning at the top, we have: 


1. Permo-Carboniferous, composed partly of calcareous, partly of Feet. 

argillaceous, and partly of arenaceous materials, the whole 

giving evidence of shallow-water origin, and characterized 

from bottom to top by fossils of Permo-Carboniterous age- - 650 
2. Upper Coal Measure, essentially made up of limestones, inter- 

spersed with a variable amount of siliceous beds, the equiva- 

lent of the Upper Coal Measure series already described in 

the Uinta region, characterized by numerous well defined Coal 

Measurenossilse = a2 - sae = ae ae = 2 iefat- 1, 700 to 2, 100 
3. Weber quartzite, a heavy body of quartzitic strata, slightly inter- 

spersed with greenish-gray slates, and containing, at both 

limits, unimportant intercalations of limestone. ------ 5, 000 to 6, 000 
4. Wahsatch limestone, blue and gray rocks, in the upper part fre- 

quently rather thinly bedded and interstratified with a few 

persistent light-colored siliceous beds and quartzites. For the 

most part the limestones forming this series are compact and 

heavily bedded, and toward the base very dark-colored and 

more thinly bedded, with a few siliceous intercalations. Coal 

Measure fossils are numerous down to 1,600 feet from the 

base, where occur sub-Carboniferous types, which occupy 

but a narrow horizon, immediately followed by fossils of 

the Waverly group, these underlaid by beds containing 

Devonian forms, the whole making a continuous single body 

ai? [hinayfiigirs 6 le Ae Se Se eee aoe 7, 000 


156 SYSTEMATIC GEOLOGY. 


5. Ogden quartzite, generally white, shading off into pale green, Feet. 

often saccharoidal, more or less associated with greenish clay 

slates and rare conglomerates..-..---------------- 1, 000 to 1, 500 
6. Ute limestone, a dark-blue, compact, fine-grained rock, contain- 

ing, a short distance below the top, Quebec fossils, which con- 

tinue nearly to the base of the series. Toward the base the 

limestone becomes shaly for several hundred feet...- 1,000 to 2, 000 
7. Cambrian shales, a bed of variable calcareous and argillaceous 

slates of varying thickness, containing Primordial fossils... 75 to 600 
8. Cambrian quartzite, an immense series of siliceous and arkose 

POCK Soop PI or RRR ee ao oe oe et pe Ie eft 12, 000 
9. Lower Cambrian slates, dark argillites, and intercalated siliceous 

SC HISES Ue yes we SNe ce ek tak Re Ree eS 800 


I purpose briefly to describe two separate sections in Wahsatch 
Range, which will serve to illustrate the succession of strata and life from 
the lowest of the Cambrian series to the close of the Paleozoic. The most 
excellently displayed of these, so far as continuity of outcrop goes, is that 
shown in the canon of Weber River, from near the mouth of Lost Creek 
down to Morgan Valley. This section shows only the upper edge of the 
Cambrian series, never exposing the deepest members. The second sec- 
tion will be that from the mouth of Big Cottonwood Carion directly across 
the range to Parley’s Park. As much of this section is on mountain sides 
and ridges, the absolute continuity of outcrop is often lost under unim- 
portant masses of débris and accumulations of soil; but the lower portion, 
namely, the Cambrian, is observed in deep continuous exposures in the 
canon cut. Besides these two sections, details of the general scheme will be 
filled up by such additional partial sections as are considered essential to 
the rounding out of our knowledge of the region. 

The base of the Weber Canon Paleozoic section is seen in Morgan 
Valley, a depression parallel with Wahsatch Range at the east base of 
the Archean mass which forms the main ridge from the region of Ogden 
nearly down to Salt Lake. Upon the eastern flank of the Archean to the 
north and south are seen resting the members of the Paleozoic, but directly 


i _ : 
_ 
; ee 
wa 
i 
7 ; 
; i C 
7 oS 
=f - 
' 7 
> 
: tat - 
= 
; - 
= 
is 
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: 7 
. T 
: : v : 7 7 7 
n 
> - B : 
we ot 
AGG? 
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7 7 a Mi hal: : 
ee, 7 A 


PALZHOZO!IC EXPOSURES. 157 


east of Farmington the Paleozoic series is eroded away very deeply, and 
its former place is overlaid by the nearly horizontal members of the Ver- 
milion Creek Tertiary, which rests directly, in evident unconformity, upon 
the Archean. On the eastern side of the valley, however, the Tertiary is 
chiefly eroded away, and the bold heights of Morgan Peak are entirely 
made up, from summit to base, of the Palzozoic series. The lower foot- 
hills, all along the eastern edge of Morgan Valley, are partially composed 
of the horizontal strata of a very late Pliocene series, and are still further 
covered up by débris which rolls down from the height to the east. 

The section observed, from the base upward, is as follows: 

1. The lowest visible outcrops of the older rocks are composed of the 
peculiar cream-colored and pinkish quartzites, overlaid by thin greenish 
siliceous argillites, very compact and having a splintery fracture. No great 
thickness of these rocks is exposed, certainly not over 200 or 300 feet, but it 
is the unmistakable summit of the Cambrian, as will be seen by future com- 
parison. 

2. Conformably overlying this is a body of limestone about 1,100 feet 
thick, the lower part composed altogether of calcareous shales, very black, 
and splintery in fracture, while the upper members are of dark and con- 
tinuous beds of limestone. This zone, too, is much obscured by overlying 
débris and soil. The outcrops are never continuous for any considerable 
length, and the extremely limited exposures yield no fossils. But, as 
will be seen hereafter, it is clearly in the position of the Ute limestone, the 
great body of the Quebec Silurian horizon. 

3. Overlying the limestone and conformable with it, as is seen at one 
exposure, is a body of white quartzite, containing more or less restricted 
zones of conglomerate, the average grain of the quartzite being very fine, 
and the color varying between pure white and grayish green. Like the two 
previous members of the section, it is chiefly covered by débris and rubbish, 
with only oceasional outcrops here and there along a line of five or six miles. 
These have the character of the low lines of cliffs, for the most part buried 
in soil, the base rarely appearing, while the backs of the strata slope east- 
ward at an angle of 30° or 40° into the hills, rapidly covered by débris. The 
thickness is estimated, by the space occupied by these scattering outcrops, 


158 SYSTEMATIC GEOLOGY. 


at 1,200 feet. Up to this point, these three members would be of little value 
taken by themselves, but their general thickness, lithological character, and 
sequence are important when hereafter compared with sections of better ex- 
posure. They occupy the low foot-hills, and their total amount of outerop 
is rather small. The strike, as shown at several points, varies a little 
both to the east and to the west of north; the dip is eastward at an angle 
of about 40°. 

4. Directly and conformably overlying the Ogden quartzite comes the 
great Wahsatch limestone, which shows continuous outcrops for several miles 
and is thoroughly exposed from summit to base, making a total single series of 
limestone of 6,500 to 7,000 feet. The most valuable part of the whole Weber 
section begins with the bottom of this limestone, which rests on a few thin 
sheets of olive-colored argillites separating it from the Ogden quartzite below. 
There seems to be no intercalation whatever of limy material at this point. 
The quartzite comes up sharply to the argillites, which are here not over 
ten or fifteen feet thick, and give way immediately to impure earthy lime- 
stones of a very dark color. Thus far, on this section, the lower 1,200 feet of 
the Wahsatch have not yielded any fossils, but at the height of from 1,200 
to 1,400 feet from the bottom of the limestone, in the neighborhood of Weber 
Station, the hills directly north of the dépét are rich in Coal Measure forms. 
This point constitutes the entrance to Weber Canon, which is cut in a nearly 
east-and-west direction transversely to the strike of the strata. The hills on 
the north side of the river rise to 2,000 and 2,500 feet above the canon 
bottom, and the Paleozoic strata edges are seen dipping eastwardly at angles 
from 28° to 45°, the outcrops slanting up the hills and sinking beneath the 
bed of the canon. At Weber Station the beds, which are about 1,300 feet 
stratigraphically above the base of the limestone, present their edges clearly 
to view, and show a varying dip of from 80° to 40°. They are here usually 
of quite pure limestone, and the strata vary in width from extremely thin 
sheets to heavy tables. So, too, they vary in their lithological condition, 
some being highly crystalline, others merely granular, and some even very 
roughly granular. 'The following forms were collected here: 

Zaphrentis Stansburyi. 
Chonetes granulifera. 


PALHOZOIC EXPOSURES. 159 


Productus symmetricus. 
Martinia lineata. 
Spirifer opimus. 
Spiriferina Kentuckensis. 
Athyris subtilita. 


Passing up the cajion, the series of limestones continues consecutively, 
without any interruption, for five or six miles, exposing 5,000 to 6,000 feet 
in thickness above the dépot. The dip varies from 35°, in extreme cases, to 
55°, but the steep dips are extremely local, and are enclosed both above and 
below by beds of the normal inclination of 40°. 

About 1,100 feet from the summit of the group, in very pure grayish- 
blue limestone of dark hue, the following fossils were obtained : 

Spirifer opimus. 
Athyris subtilita. 
Terebratula bovidens. 
Productus prattenianus. 
Aulopora sp.? 


Nearly 800 feet from the top were collected— 


Terebratula bovidens. 
Productus prattenianus. 
Aulopora sp.? 


Also 500 feet from the top are Terebratula bovidens and Athyris subtilita. 

About 300 feet from the summit of the series are some extremely 
dark beds, which emit a feetid odor upon being struck with a hammer, and 
are intercalated with very impure arenaceous limestones. These contain 
numerous Spirifer opimus and Athyris subtilita. 

The limestones at 1,000 feet from the top enclose a series of thinly 
bedded but heavily blocked quartzites, which contain two or three sheets 
of small pebbles. These, however, are very thin and localized. The 
quartzite is more properly indurated sandstone and occupies a belt 150 
feet thick. In general, the upper 1,000 or 1,500 feet of this limestone series 
are made up of thinly bedded rocks, less pure than the strata below, and 


160 SYSTEMATIC GEOLOGY. 


more or less intercalated with siliceous zones. Some of the beds are also 
considerably argillaceous. It is noticeable that while the massive limestones 
below are quite uniform in dip, the intercalated region is subject to great local 
disturbances. It would seem that the limestone beds are able to undergo 
compression with less contortion than the more siliceous beds. As a conse- 
quence, the included siliceous zones are wavy, and exhibit extreme irregu- 
larity of dip, while the limestones enclosing them on both sides maintain an 
even inclination. Below this upper thousand feet the materials are much 
more uniformly calcareous, and the siliceous zones are never pure enough to 
show any distinct sandstone strata. Asa whole, the color of the series is dark. 
From the Weber dép6t to the summit of the series, therefore, the whole of 
this immense limestone is characterized by distinct Coal Measure forms, 
while the lower 1,200 or 1,300 feet have here yielded no fossils. This is no 
doubt due to the fact that it touches the edges of the foot-hills, and, like 
the three series described below, is largely covered with débris. Particular 
attention should be paid to the fact of the contortions and disturbances in 
the region of sand and quartzitic beds in the upper 1,200 or 1,000 feet of 
the series, as those phenomena are persistent over considerable areas of the 
Wahsatch, and will hereafter be described more particularly in some of the 
partial sections, where their recurrence is marked by most interesting inter- 
nal plication. The closing members of the Wahsatch group are arenaceous 
limestones, with a brilliant brick-red color. 

5. The passage from the Wahsatch limestone into the Weber quartzite 
is made in perfect conformity, and, as the beds clearly evidence, with undis- 
turbed consecutive deposition. Above the reddened and arenaceous sum- 
mit of the Wahsatch limestone are a few intercalations of siliceous lime- 
stone. The Weber beds at this point dip about 40° to the east. In this 
lower zone are sheets of conglomerate, the pebbles of which are usually 
small and composed of white quartz. The general appearance of the 
quartzite zone is here that of a coarse, rather gritty sandstone, unevenly 
compressed into quartzite. The bottom of the series is prevailingly red for 
about 250 feet, and averages coarser than the material above. Over the 
red is a very finely laminated white and grayish quartzite, quite uniform in 


texture, and with only the most sparing enclosures of pebbles. Above this 


PALZOZOIC EXPOSURES. 161 


point the series rapidly decline in dip to an inclination of only 16° to 20° 
to the east, accompanied by slight undulations. The curve from the steeper 
to the gentler dip is very gradual, and is unaccompanied by dislocations. 
There seems to be also a very small amount of local cracking of the strata. 
This low dip is held for about two miles up the canon, the strata becoming 
thicker and more heavily bedded, the texture of the quartzites more and 
more dense, and the conglomerates occurring at less frequent intervals. 
A mile and a half east from the base of the series there is scarcely any 
conglomerate at all, and the rock is a true quartzite of whitish or greenish 
hue, developing on many of its weathered surfaces a peculiar dark brown 
stain which looks like the oxydation of manganese. At the lower railway 
tunnel an interesting sharp double curvature is described by the strata. 
From the easterly dip of 16° they pass under a short shallow synclinal, 
rising on the reverse dip of about 20° for 100 feet or so, then, curving over 
an anticlinal, dip again to the east, from which point the easterly dip is 
maintained at an angle of 50° to57°. There isa small development of lime- 
stones here, quite black, and sufficiently siliceous to scratch glass, though 
effervescing under acids. This singular black rock is found to contain 83 
per cent. of silica, 5 of organic matter, and 12 of carbonate of lime and 
magnesia. Above the tunnel are about 1,500 feet of massive quartzites of 
greenish-white hue, closely resembling the similar rocks at Mount Agassiz. 
The strike here deviates more and more to the north in ascending the canon. 
Throughout the whole 5,000 feet of this series no fossils are found. Toward 
the top are numerous peculiar holes in the rock, which seem like the cavities 
left by decomposing fossils, but the evidence is too slight to be of value. 
It is from the characteristic occurrence of this remarkable bed of quartzite 
at this locality that the name Weber quartzite has been given to the body. 
It is here essentially a quartzite, although toward the base rather more truly 
an indurated sandstone. The thickness, which we estimate in this exposure 
at 5,000 feet, represents the minimum observed section of this series, where 
both its lower and upper limit can be observed. It likewise represents the 
most extreme lithological result in the direction of the quartzite; and I am 
convinced that those two conditions are expressions of a common cause— 
that rocks made up of siliceous detritus may be compressed to half the 
1B ae 


1 oy SYSTEMATIC GEOLOGY. 


thickness of the original deposit in passing from an incoherent sand rock to 
the strictly crystalline condition of quartzite. 

6. Conformably overlying the quartzite is a very heavy bed of much 
altered gray limestone from 600 to 700 feet thick. The bedding-planes 
are often entirely obliterated, and the material extremely crystalline, showing 
traces of great interior disturbance. The lower beds show a true conformity 
with the underlying quartzite. One or two hundred feet up in the series 
the alteration of the limestones reaches its maximum, and on the heights to 
the north of the cation it approaches a white marble. It is riven with cracks 
in every direction, but shows no trace of the intrusion of foreign chemical 
agents. South of the canon a few fossils were collected in a badly pre- 
served condition, but sufficiently distinct to be referred by Prof. Meek with- 
out hesitation to the Upper Coal Measure forms. One of these is a Sprri- 
ferina Kentuckensis; the other S. prattenianus. The gradual deviation 
of the strike from true north-and-south to a little east of north, already 
mentioned in the Weber quartzites, here reaches a direction of north 15° 
east. The average colors of these limestones are creamy grays, inclin- 
ing often to white in the more crystalline portions. A deep ravine which 
enters the canon from the north cuts diagonally across the upper part 
of the Upper Coal Measure limestones down into the Weber quartz- 
ite, and displays their conformable contact very well. Here the lime- 
stones are still more altered, and may be called a crude marble. The quartz- 
ites are also more disturbed, and show the effects of intense compression. 
This region of maximum disturbance and metamorphism is directly in the 
axis of the change of dip already mentioned as shown below the lower rail- 
road tunnel. Passing over this curve to the west of the head of the ravine, 
the limestones are again seen conformable to the diminished dip of the 
quartzite, inclining at about 16°. On the heights south of the river, where 
the whole formation passes under the horizontal beds of Eocene conglom- 
erate, this great bed of limestone is less altered, and shows many strata of 
pale yellow and drab color, resembling their equivalents, the lower drab 
limestones of the Upper Coal Measure series of the Uinta. Overlying 
this main body of 700 feet of limestone is a series of yellow shaly lime- 
stones 175 feet thick. This rock is extremely brittle, and, owing to the 


PALASOZOIC EXPOSURES. 163 


uneven strain to which it has been subjected, is shivered into pecul- 
iar splinters, so that the surface of each stratum, instead of being the 
natural smooth plane of deposition, is a series of minute waves and troughs, 
like broken wave-marks. This shaly structure is obviously due to uneven 
pressure. ‘The surfaces of the fragments are not infrequently stained a pale, 
sulphur yellow. Overlying these calcareous shales, as heretofore quite 
conformable, is a series of sand and mud rocks, all more or less calcareous, 
varying in color from chocolate to olive, with red argillaceous sandstones, 
the whole about 225 feet thick. It has the appearance of a comparatively 
shallow-water deposit, made of argillaceous material, limestone, and sand, 
the thickness of individual beds being unusually limited. There are very 
many beds not over an inch thick On the upper surface of the strata, at 
several horizons, ripple-marks are preserved with unusual distinctness, and 
on a scale of fineness not often seen, the distance between the wave and 
trough being frequently not over an inch or an inchand a half. Alternating 
dark chocolate and olive-colored shales form the lower 200 feet of this 
group, while the upper 25 or 30 feet are pretty solid sandstone. Over 
these, still conformable, are 100 feet of yellow and olive calcareous shales, 
which are so earthy as usually to decompose, yielding a bad outcrop. 
Above this is a bed of bluish-gray limestone, rather compact, about 150 
feet in thickness. Next come 20 feet of reddish-brown clayey sand, hardly 
compacted into rock, containing thin stony seams intercalated at intervals in 
the soft, easily eroded matter. This is immediately followed by 75 feet of 
a yellowish-gray, brittle, easily decomposed limestone Next above are 100 
feet of light-colored, very thinly bedded limestones, that give way to 100 
feet more of dark, siliceous, tough limestone, which breaks under the ham- 
mer with great difficulty, yielding an exceedingly rough, ragged fracture. 
In this were obtained a few fragments of fossils, made out by Professor 
Meek to be of the genus Bellerophon; and the highly siliceous character 
of the bed, closing as it does the Upper Coal Measure series, leads me to 
correlate it with the siliceous Bellerophon limestones already described 
in the Uinta. 

7. Next above in sequence, and apparently with entire conformity of 
dip angle, although there are slight indications of erosion upon the surface 


164 SYSTEMATIC GEOLOGY. 


of the siliceous limestone prior to the deposition of the overlying shales, 
follows a body of-variable shales, thin seams of limestone and mud and sand 
rocks, the whole being of shallow-water origin and displaying ripple-marks, 
comprising 620 feet of conformable beds. At three localities in this series 
were obtained fossils of Permo-Carboniferous facies, including — 


Aviculopecten McCoyi. 
Aviculopecten oxidaneus. 
Aviculopecten n. sp. 
Schizodus ovata. 
Myascites Weberensis. 


Directly above the siliceous limestone, which I consider to be the 
equivalent of the Bellerophon limestone, are shales carrying beds of argil- 
laceous sandstone three or four feet in thickness, which vary in color from 
chocolate to olive, the whole being about 100 feet thick. The olive-colored 
shales carry the same remarkably preserved ripple-marks as were ob- 
served below the Bellerophon limestone, but they are far larger than 
those above described. Above this series of chocolate and olive shales 
are 200 feet of soft muddy shales, containing thin beds of argillaceous 
limestone, also ripple-marked, and limited layers of mixed arenaceous 
and impure limestones. Still above these are 250 feet of buff and gray 
sandstone, usually made of extremely fine material held together by more 
or less argillite, and alternating with fine beds of earthy argillaceous 
shales, the whole capped by a thin siliceous series, almost a quartzite, 
70 or 80 feet in thickness. The series of Permo-Carboniferous shales 
varies in dip from 48° to 60°, rising in some local cases as high as 70°. The 
capping bed of quartzitic sandstone is directly and conformably succeeded 
by the red beds of the Trias, which will be found described in the chap- 
ter on Mesozoic formations. 

Leaving out of consideration the thickness of beds which at the base 
are but very obscurely exposed, below the bottom of the Ute limestone 
(No. 2 of the described series), and counting from the bottom of that lime- 
stone, we have in this single section to the top of the Permian 16,000 feet 
of conformable strata, characterized by Permo-Carboniferous fossils in the 


PALZOZOIC EXPOSURES. 165 


upper 620 feet; and in the next 1,600 feet, Coal Measure fossils related 
to the forms of the Upper Coal Measures, though very scarce and very 
fragmentary, owing to the physical condition of the rocks, which are 
highly altered. ‘Then comes the Weber group, made up of 5,000 feet of 
quartzite, occupying the position of the Middle Coal Measures, underlaid 
by more than 5,000 feet of Coal Measure limestones, comprising the upper 
five sevenths of the Wahsatch limestone. From this section we obtained, 
first, a clear expression of the stratigraphical sequence of the series; sec- 
ondly, the upper and lower limits of the Coal Measure series, which give 
for that member here a thickness of about 12,000 feet. Of the 16,000 feet, 
about 9,100 feet are limestone, 6,200 are of purely siliceous material in the 
form of sandstones and quartzites, and 700 to 800 feet of argillaceous and 
arenaceous mud rocks, characterized by more or less calcareous material. 
It is also noticeable that, with the slight exception of the thin bed of slate 
which underlies the Wahsatch limestone and separates it from the Ogden 
quartzite, and a few slightly argillaceous limestones in the upper 1,000 feet 
of the Wahsatch body, all the shales and argillaceous material are confined 
to the upper region of the Coal Measures directly under the Bellerophon 
limestone, and to the Permo-Carboniferous which immediately succeeds it. 

I will now give a section observed between the mouth of Cottonwood 
Cation and Parley’s Park, the most extended and instructive stratigraphical 
exhibition of the Paleozoic series in the Fortieth Parallel area. 

1. A glance at Map III. of the geological series will discover a consider- 
able body of Cambrian occupying the lower half of Big Cottonwood Canon. 
The same formation is seen to recur upon the south side of the granite 
ridge which separates the two Cottonwood canons, extending part-way 
down to the bed of the canon, and again recurring upon the heights 
northwest of Alta. The deepest section of this body is offered on the 
lower course of Big Cottonwood Canon, which lies wholly in the Cam- 
brian for five miles. The strike of the rocks is diagonal to the canon, 
so that the exposures on the canon walls and in the lateral ravines display 
both the edges and the backs of the beds, giving an excellent idea of 
their physical condition. The canon in its zigzags often follows the strike 


of the rocks for a short distance, and then cuts either perpendicularly or 


166 SYSTEMATIC GEOLOGY. 


obliquely across them. The estimate of the general thickness of the body 
as exposed here is made by laying down a great number of local observa- 
tions on the map, and deducing an average dip and strike, to which is 
applied the transverse distance of the outcrop, and the result gives about 
12,000 feet. While an accurate, detailed measurement is probably impos- 
sible, this estimate is a sufficient approximation to truth for all our purposes. 
Near the mouth of the canon, to the south of which the Cambrian series 
overlie the granite and Archean body unconformably, are seen the lower- 
most members of the series, here formed of a body of dark blue and purple, 
and dark olive-green, often almost black slates, largely made up of fine- 
grained and thinly laminated argillites which alternate with zones more or 
less siliceous, the whole measuring from 800 to 900 feet in thickness These 
constitute our Lower Cambrian slates. Conformably above them are 8,000 
to 9,000 feet of mixed siliceous schists and argillaceous schists, in beds vary- 
ing from a few inches in thickness to heavy strata eight or ten feet thick. 
They are prevailingly siliceous, but over a great thickness the alumina pro- 
portion is high. One of these intermediate forms gave on analysis 60 per 
cent. of silica, the other constituents being mostly alumina, with a little iron, 
lime, and alkalies. Above these varying schists are about 3,000 feet of true 
quartzite, capped by 200 feet of schistose rocks, quite micaceous toward the 
bottom. Among the beds near the top of Twin Peaks, a high summit south 
of the canon, is a series of the strata of micaceous quartzite, in which the 
mica occurs rather sparingly in fine brilliant specks, apparently muscovite. 
It imparts a decidedly fissile structure to the rock. On the peak next east 
is found a dark-blue, argillaceous slate, in which there is a considerable 
development of phlogopite in dark bronze crystals. Throughout the region 
of Twin Peak schists which directly underlie the highest quartzites of the 
‘ambrian, are numerous zones that closely approach mica schist. In the 
ravines that lead down the northeast side of Twin Peaks these mica-bearing 
schists, which are not sufficiently charged with the mineral to be called a 
mica-schist, are observed underlying the upper quartzites. 
An excellent section of the Cambrian schists is obtained from the mouth 
of Big Cottonwood Canon, in a northeasterly direction across the spur which 
divides the waters of Cottonwood Creek from those of Mill Creek. About 


PALM OZOIC EXPOSURES. 167 


the same estimate of thickness is formed from an examination of this ridge, 
namely, that from the dark bottom slates to the top of the argillaceous slates 
which cap the body, there is an exposure of about 12,000 feet. 

Although search was made throughout these schists as carefully as our 
time would permit, no fossils were obtained, and the reference to Cambrian 
will be explained later in the chapter. 

The series consists essentially of four members: the bottom slates, 800 
feet; varying siliceous and argillaceous schists containing some mica-bearing 
zones, 8,000 or 9,000 feet; salmon-colored and white quartzites intercalated 
with dark schists, 2,500 to 3,000 feet; and the capping schists of 200 feet, 
which are partly argillaceous and calcareous and partly mica-bearing argil- 
lites. The dip as shown in Cottonwood Canon is very high, in the region 
of 60° near the mouth of the canon, declining eastward, so that the higher 
members of the groups directly under the Silurian limestone in Big Cot- 
tonwood Canon slope to the east about 45°, while across the ridge just below 
Alta, in Little Cottonwood Canon, they preserve the steep dip of 60°. The 
contact between this series and the underlying unconformable mass of 
granite and Archzean schists is extremely interesting, and from its situation 
offers remarkable opportunities of studying the early contours of the older 
rocks. From the mouth of Cottonwood Canon the line of contact rises 
upon the ridge to the south, forming the divide between the two Cotton- 
wood canons, and circles across the divide around the base of Twin Peaks, 
leaving the upper 2,000 feet of the mountain mass Cambrian, and the 
lower 3,000 feet on the Little Cottonwood side granite. The line of 
contact is nearly horizontal, and extends back six miles to a little below 
the town of Alta, successively higher members of the Cambrian series 
resting against the granite, until at last the ancient series rises into contact 
with the Silurian limestone, which conformably overlies the Cambrian. 
This is well shown in the lower section at the bottom of Map III. 

2. Next above the Cambrian lie 1,000 feet of Ute limestone, which for 
the most part is very light-colored, highly crystalline, and characterized by 
peculiar cloudings of color that extend across the beds. Near the bottom of 
the series, and at one or two horizons near the top, it is noticeable for contain- 


ing a large proportion of tremolite, and under the microscope it is seen to 


168 SYSTEMATIC GEOLOGY. 


be highly siliceous, the silica appearing as rounded glassy grains of pellucid 
quartz. The outcrop extends up the hills on both sides of the canons, and 
to the south is conspicuous upon the divide, from which it descends into 
Little Cottonwood and in the valley a little way below Alta exposes a 
fine precipitous cliff, the result of a fault. Here again are seen the same 
highly crystalline, almost marble-like condition and the same prevalence 
of tremolite and silica. Under these circumstances it is not at all remark- 
able that the bed contains no fossils; but it is unquestionably Silurian, as 
will be seen later. 

3. Above this Ute limestone occurs the white granular body of Ogden 
quartzite, which is here reduced in thickness to about 800 feet. It may be 
traced up the hills to the south, and forms an interesting saddle on the 
ridge-top between the Ute limestone and the bold masses of Wahsatch 
limestone which directly overlie it. Here are but limited traces of the thin 
body of greenish argillites that farther south, in the region of Rock Creek, 
were found on both sides as bounding-beds of the Ogden body. 

4. Immediately above this is Wahsatch limestone, which forms the 
high ridge north of the canon, and is traceable south against the granitic 
slopes of Mount Clayton. In the whole semicircular sweep which the 
Wahsatch limestone here describes around the Archeean body are the most 
interesting changes of molecular condition. The ridge to the north of Big 
Cottonwood shows a scarcely altered dark limestone, in which the fossils 
are preserved, while toward the south it becomes white marble, and near 
Mount Clayton is intersected by numerous dikes of granite-porphyry. 
The lower beds are pretty sharply defined from the Ogden quartzite; but 
themselves contain a little granular quartz, which remains upon dissolving 
the limestone in acids, and is partially rolled, though in general angular. 

The lower Wahsatch beds in Big Cottonwood Canon are heavy, and 
owing to the high state of alteration contain no fossils. On the ridge to 
the south, at the Reed & Benson Mine, about 1,300 feet from the base of 
the series, were found the following species characteristic of the Waverly: 


Spirifer Albapinensis. 
Spirifer centronatus. 


PALMOZOIC EXPOSURES. 169 


Athyris planosulcatus. 
Athyris Clayton. 
Euomphalus Utahensis. 
Terebratula Utahensis. 
Cryptonella sp.? 


On a horizon a little above that of the Reed & Benson Mine were 


obtained the following distinctive Coal Measure forms: 


Spirifer cameratus. 

Spirifer planoconvexus. 
Spirifer sp.? (like disjunctus). 
Syringopora sp.? 
Diphyphyllum. 


And still higher up, about 2,500 feet from the base of the series — 


Spirifer lineatus. 

Spirifer sp.? (like disjunctus). 
Athyris subtilita. 

Euomphalus sp.? 

Zaphrentis sp.? (like centralis). 


On the summit of the ridge above the Flagstaff Mine, a bed of white 
calcareous quartzite in Wahsatch limestone is full of indistinct cylindrical 
cavities, the casts of fossils, and frequent Spirifer cameratus. 

‘On the heights to the south of the canon are some Z-shaped folds in the 
upper part of the Wahsatch beds, similar to occurrences which will be 
described in the Ogden Canon section. 

On the north side of the cation bottom, in the less altered limestones 
about 2,000 feet from the top of the series, were obtained — 


Chonetes granulifera. 
Productus Nebrascensvs. 
Productus pertenuis. 
Productus symmetricus. 


170 SYSTEMATIC GEOLOGY. 


Farther west on the strike, at about the same horizon, were obtained — 


Productus semireticulatus 
Spirifer ? 

Zaphrentis ? 

Crinoids. 


From the very uppermost beds directly under the lower members of 
the Weber quartzite, on the hill-top north of the Big Bend of Cottonwood, 


were obtained — 
Productus prattenianus. 


Productus semireticulatus. 


5. Conformably over the Wahsatch limestone is the enormous body of 
Weber quartzites with shght intercalations of conglomerate, and near the 
upper limits of the series a few thin, argillaceous schists. In the region of 
the schists, which cannot be less than 4,000 feet up in the series of quartz- 
ites, the siliceous beds themselves are interestingly banded like ribbon 
jasper, a feature which is worth noticing as occurring farther east in the 
Uinta, but as not observable in the Weber quartzites to the north or west 
of this point. The area occupied by the Weber at the head of Cottonwood 
Canon is cumbered with an immense amount of glacial and modern débris 
obscured by growths of coniferous timber, and in general it is impossible 
to measure the thickness accurately. Where observed, the dip, like that 
of the underlying series, approximated to 45°, but occasionally was some- 
what higher. Judging by the average dip and the area in which only 
quartzitic strata outcrop, there cannot be here less than 6,000 feet of the 
Weber formation. This body may be traced to the northwest until its 
steep edge appears against the foot-hills of Jordan plain. By a general 
examination of the ridge it becomes clear that it is pure quartzite without 
important intercalations, except at the bottom, where for several hundred 
feet. the passage from Wahsatch limestone into quartzite is made by thick 
intercalations of seven or eight beds of limestone. This feature, unnotice- 
able to the north, recurs to the south, and is characteristic of the junction 
of the two formations in this longitude. 


6. Continuing from the Big Bend of Cottonwood Caiion in a northwest 


PALHOZOIC EXPOSURES. 171 


direction toward Parley’s Park, the contact of the upper limit of the Weber 
quartzite with the heavy beds of drab limestone which form the lower por- 
tion of the Upper Coal Measures, is distinctly observed; but owing to the 
forest and débris, only a few fossil forms were obtained, and those in a 
much-weathered, unsatisfactory condition. Yet the character of the lime- 
stone, and its conformable position directly over the Weber, clearly refer it 
to the base of the Upper Coal Measure series. A continuous belt of lime- 
stone, about 1,200 feet thick, is here exposed, of which the upper portion 
is rather finely stratified and shaly, and bears Bellerophon carbonarius. 

7. Directly over this is a series of calcareous shales and ripple-marked 
argillites with yellow shale rocks, and at the summit of the series a consider- 
able body of quartzitic sandstone which directly underlies the red Trias. 
In the mud rocks and in the caleareous shales on the extreme foot-hills of 
Parley’s Park, in a position about three hundred feet below the ‘Trias, were 
obtained a Bakevellia, probably parva; a Eumicrotis, probably Hawni; and 
an Aviculopecten, like parvula. Owing to the amount of forest and débris, it 
is impossible to be sure that these upper series, which correspond with 
the Permo-Carboniferous shales of the Weber section, have not been redu- 
plicated by a fault, for there seem to be, as nearly as can be estimated, 
about 9U0 feet. 

The principal points of interest of this section are, first, the deep expo- 
sure of rocks which we have referred to the Cambrian, lying conformably 
below the Ute Silurian limestone, affording us the deepest view of the Pal- 
weozoic beds that we get anywhere upon the Fortieth Parallel; secondly, the 
absolute stratigraphical parallelism between this and the Weber section ; 
thirdly, the fact that we obtained, as in the Weber section, Coal Measure 
fossils down to within about 1,300 feet of the base of the Wahsatch lime- 
stone, and at that horizon was established by ample evidence the existence 
of the Waverly group; fourthly, the lithological and faunal identity of the 
Permo-Carboniferous shales with those of the Weber. Asa whole, the sec- 
tion is not so continuously exposed and the opportunities for measurements 
of the thickness of beds are less favorable than in Weber Canon The 
Wahsatch limestone seems to be thicker than in the Weber, while the Ogden 
quartzite has diminished from 1,000 to 800 feet © Otherwise a comparison 


172 SYSTEMATIC GEOLOGY. 


of the sections will show an approximate identity. As in the Weber sec- 
tion, there is absolutely no nonconformity from the base, 30,000 feet up to 
the very summit. 

South of Lone Peak the great body of Wahsatch limestone already 
described in the Cottonwood region completes a semicircle about the 
granite mass, and then abruptly trends in a southeasterly direction, form- 
ing the whole range from base to summit. The region is here compli- 
cated by faults parallel to the strike, as well as transverse, so that an accu- 
rate measurement of the thickness of the series is impossible. As at the 
north, Coal Measure fossils characterize the beds to within 1,200 or 1,300 
feet of the base of the series. That base is exposed very clearly north of 
the town of Provo; and along the whole eastern flank of the range back 
of Provo Peak the limestone is seen to pass by a series of intercalations 
into Weber quartzite. A remarkably good instance of these intercalations 
is shown on Tim-pan-o-gos Peak. The peak itself is a narrow ridge 
trending parallel to the strike of the body, namely, a little west of north, 
and reaches an elevation of 11,937 feet. It falls abruptly down to the 
east and west from 3,000 to 5,000 feet, and is composed of approximately 
horizontal strata of the Wahsatch series. The beds forming the upper part . 
of the ridge consist of repeated alternations of layers of limestone and 
limestone shales, with light-colored quartzites and siliceous shales. This 
intercalated passage into the Weber is clearly recognizable along all this 
region south of Clayton’s Peak, and represents a much more gradual tran- 
sition than in the Weber section, where the change from Wahsatch lime- 
stone up into Weber quartzite is characterized by a sudden break and a 
few unimportant intercalations. The interbedded zone carries numerous 
fossils in the limestone members, which in general have been changed into 


a white calcitic material. Among the species recognized were — 


Spirifer cameratus. 
-Athyris subtilita. 
Productus semireticulatus. 
Discena sp. ? 


The mixed zone, varying from 400 to 550 feet, includes about forty 
intercalations. The well known layer of white vitreous quartzite in the 


ob 


+ 


PALA OZOIC EXPOSURES. Lee) 


upper part of the Wahsatch limestone and a little below the transition-zone 
is constant here. 

Plate X. represents the front face of the Wahsatch at Provo Fall; the 
cascade is here about 600 feet high, tumbling over escarped edges of the 
Wahsatch limestone group. 

The following few other illustrations are selected from Wahsatch local- 
ities, to add data to the general section. 

On the foot-hills a short distance to the north of Camp Douglas, 
directly underlying the red Trias limestone, are seen the series of the 
Permo-Carboniferous and Upper Coal Measures. Here was obtained 
Aviculopecten Weberensis. Farther south, on the spur between Parley’s 
and Emigration canons, is a local anticlinal, a minor contortion in the great 
series of the northerly dipping strata which extend thence to the mouth of 
Cottonwood Canon. Conformably included within the anticlinal fold of 
the red Trias sandstones is a small body of the characteristic red beds and 
clay shales of the Permo-Carboniferous, containing the following: 


Aviculopecten Weberensis. 
Aviculopecten curtocardinalis. 
Aviculopecten MeCoyt. 
Aviculopecten parvula. 
Sedgwickia concava. 
Eumicrotis Hawn. 

Myalina permiana. 

Myalina aviculoides. 


North of Clayton’s Peak, and directly surrounding the eastern side of 
the body of granite, are seen the heavy beds of the Weber quartzite, here 
very much iron-stained and showing evidences of severe alteration. The 
general strike describes a complete curve around the granitic mass of Clay- 
ton’s Peak, with its convexity toward the east. The rocks east of the peak 
dip directly east under the Provo trachytes, and make with the westerly 
dipping quartzites of the Uinta an unquestionable synclinal, through whose 
faulted axis bodies of trachyte have appeared. 

About four miles up City Creek Canon, Ute Silurian limestone is 


174 SYSTEMATIC GEOLOGY. 


seen between Cambrian schists and Ogden quartzite. It is here from 1,000 
to 1,100 feet in thickness, and at a horizon about 600 feet from the bottom 
yielded specimens of Dikellocephalus Wahsatchensis, a fossil characteristic in 
this region of the Quebec age. 

Upon the high summit of the Wahsatch, east of Centreville, uncon- 
formably overlying the Archean gneisses, is a body of salmon-colored 
quartzite, containing large gritty grains of pellucid quartz, and underlaid 
by a dark, heavy bed of purple quartzite. The salmon-colored quartzite is 
about 600 feet thick, and is overlaid by a few calcareous shales, which are 
immediately succeeded by Ute limestone 1,000 feet thick, showing the con- 
formable transition from Cambrian to Silurian. 

The Cambrian recurs on Ogden Peak, where heavy quartzitie beds, 
with an easterly dip of 60°, lie upon the steep edges of Archzean bodies 
which stand about 75° to the west. Near the top of Ogden Peak the 
Cambrian is characterized by a well defined bed of compact conglomerate, 
containing remarkably smooth pebbles of quartz. From this point north 
for twelve or fifteen miles, looking at the range from the west, the Archean 
gneisses may be seen to be overlaid by an unconformable body of strata 
dipping to the east, which represent the edges left by the great fault that 
has depressed the western half of the range. Of these conformable strata, 
the uppermost, northeast of Ogden, are Wahsatch limestone, while the 
lowest exposure is of Cambrian of varying thickness. Here, from the 
study of the contact between the Cambrian and the Archean, it is clear 
that the Archeean itself was shaped into rather elevated topographical forms, 
and that the Cambrian was deposited over them all, submerging the entire 
ridge. Supposing the uplifted Cambrian back in a horizontal position, the 
present exposed contacts give an idea of the pre-Cambrian, Archean to- 
pography, and it is evident here that there were Archean peaks of 3,000 
and 4,000 feet, while an examination of the nonconformable contact in the 
region of Cottonwood Canon shows a steep mountain face of 30,000 feet ; 
and in the deposition of the Cambrian against these slopes it is evident that 
there was no tendency on the part of the sediment to conform at all to the 
ancient surface. 


Ogden Canon offers an admirable partial section of the Palseozoie. 


PALMOZOIC EXPOSURES. 175 


1. Dioritie gneisses, the prominent feature of the Archzean near 
the mouth of Ogden Canon, are unconformably overlaid by Cambrian 
quartzites striking north 30° to 35° west and dipping 60° to 65° eastward. 
Here are about 1,000 feet of quartzites, overlaid by 100 feet of siliceous 
and argillaceous shales, which in passing up become decidedly calcareous, 
showing an evident transition into the overlying Ute limestone. The occur- 
rence of these argillaceous and calcareous shales here is well shown on the 
south bank of the cation, and is of importance, since they form the stratum 
in which the uppermost Primordial forms are found elsewhere. Throughout 
the lower part of the exposure the quartzite is of uniform lithological habit, 
and smooth, even bedding. It is exceedingly compact, and the quartz grains 
which compose it are sometimes visibly rounded. In other words, the orig- 
inal figure of the grains of sediment has not been entirely obliterated and 
compressed into a uniform crystalline mass, as is the case with nearly all the 
Archean quartzites examined by us. The tints are light-gray in the lower 
horizon, inclining to salmon above, due to oxyd of iron upon the stratum- 
planes. In the upper part of the series, corresponding to the conglomerate 
horizon on the top of Ogden Peak, are seen distinct beds of conglomerate, 
made of evenly worn oval pebbles of gray, red, brown, and white jasper, 
reaching two or three inches in diameter. Both here and in the conglom- 
erates which are displayed on the east side of the Wahsatch, under the Ute 
limestone near Centreville, the pebbles are interesting for the evidence they 
give of the great pressure to which the quartzites have been exposed. They 
are often flattened and elongated, and in some cases two pebbles are com- 
pressed so as to overlap each other. In some instances three or four pebbles 
are compressed into one solid mass, penetrating each other as if absolutely 
plastic. Throughout all these distorted and compressed pebbles there is no 
evidence of cracking. The argillaceous shales, which here, as elsewhere, 
close the Cambrian series, are exceedingly fine-grained, are of prevailing 
olive and greenish-gray color, and are identical with the beds from the 
same horizon which underlie the Ute limestone at Quebec Peak, at the 
forks of the Muddy. 

2. Above these are twenty-five feet of more characteristically calcareous 
shales that pass up into well defined limestone, which is thicker than to the 


176 SYSTEMATIC GEOLOGY. 


south, reaching 1,200 to 1,500 feet. Tere, on the hill-sides to the south 
and north of Ogden River, is an excellent consecutive outcrop of the 
material forming the Ute limestone. As a whole, it is here, as in the region 
of Cottonwood, distinctly a siliceous limestone, and although formerly burned 
for lime was found to yield too siliceous a product. About 3800 feet above 
the base is a well marked zone, twenty or thirty feet thick, of argillites 
similar to those which mark its separation from the Cambrian. Below these 
twenty feet of shales the general character of the limestone is more shaly 
than above. Directly over them is a dark-blue limestone, overlaid by a 
nearly white series of granular crystalline beds, the upper portion of which 
is more or less characterized by shales. The only fossils found here were 
highly altered Stromatopora. 

3. The Ogden quartzite, which directly overlies the Ute limestone, has 
here a thickness of from 1,250 to 1,350 feet. It is pale-reddish or yellowish, 
and conspicuous for a multiplicity of jointing-planes. Subjected to chem- 
ical analysis, it yielded 77.79 of silica, the remainder of alumina, lime, and 
alkalies. About midway in the formation is a thin bed of white marble, 
above it a thin series of olive-colored, argillaceous shales. 

4, From the summit of Ogden Peak to the head of Ogden Canon ex- 
tend the massive, continuous beds of the Wahsatch limestone, which are 
displayed particularly on the north wall of the canon in precipitous cliffs 
2,000 to 2,500 feet above the level of the river. Immense piles of débris, 
fully 2,000 feet in height, obscure many of the lower strata. As a whole, 
the beds are coarsely crystalline, often siliceous, sometimes cherty, and here 
and there characterized by argillaceous, muddy impurities. About 5,000 
feet from the base of the series, and near the top of the canon, we reach 
the siliceous zone already described in the Weber section, and here occurs 
a remarkable series of plications. The impure siliceous zones are plicated 
in the form of the letter Z, the amplitude of the folds being about 500 feet. 
The beds directly under the siliceous zone, although entirely conformable, 
show the effect of this crumpling but very slightly, and in the overlying 
strata this influence gradually dies out, leaving the higher members abso- 
lutely conformable with the undisturbed region below the siliceous zone. 
Twelve hundred feet from the base of the limestone here, or practically at 


PALHOZOIC EXPOSURES. ee F 


the identical horizon at which the Waverly fossils were obtained at the 
Reed & Benson Mine, we collected the following: 


Productus sp. ? 
Spirifer Albapinensis. 
Spirifer centronatus. Waverly. 
Athyris planosulcata. 

Euomphalus Utahensis. | 
Streptorhynchus inequalis. 


i Devonian. 
Proetus peroccidens. 


While this series of fossils, as a whole, has an unmistakable Waverly 
facies, the occurrence of the last two, which are essentially Devonian forms, 
marks this horizon as the turning-point between the Devonian and the Wa- 
verly. In this connection it should be mentioned that at about the same 
horizon in Wahsatch limestone at Rock Creek was obtained Spirifer cen- 
tronatus, a well defined Waverly species also occurring in the White Pine 
District at the base of the Waverly. Farther up, directly above the flexed 
region of the siliceous zones near the head of the canon, was found a new 
species of Zaphrentis associated with true Lower Coal Measure forms. 

The horizon of the Waverly is again shown in Logan Cation. Cache 
Valley is a broad anticlinal formed of the Paleozoic series, from the Cam- 
brian well up into the Wahsatch limestone. The axis of the synclinal is 
occupied by horizontal beds, which obscure the uppermost members of the 
Wahsatch. In the low beds which are exposed near the mouth of the 
canon, about 1,400 or 1,500 feet above the lowest exposures, at a horizon 
which must be very closely that of the Waverly, in Ogden Canon, were 
obtained the following fossils : 


Chonetes Loganensis. 
Rhynchonella pustulosa. 
Euomphalus latus, var. lacus. 
Spirifer Albapinensis. 
Spirifera centronata, 
Proetus peroccidens. 
Proetus Loganensis. 

12 


178 SYSTEMATIC GEOLOGY. 


Higher in the same limestones, in the horizon of the Lower Coal Meas- 
ures, were obtained a small species of Productus, Zaphrentis Stansburyi, and 
Lithostrotion. 

From Copenhagen to Call’s Fort the Cambrian, with the Ute limestone 
and overlying Ogden quartzite, is seen outcropping very distinctly. The 
contact between the Cambrian and the Ute limestone slopes down to the 
plains, and is depressed under the Quaternary directly at Call’s Fort. The 
quartzite here has a high vitreous lustre, conchoidal fracture, and extremely 
fine texture; its prevailing colors are decidedly salmon. The strike of 
the quartzites and limestones is approximately north 20° west, diagonally 
crossing the range. Here the upper member of the Cambrian directly over- 
lying the quartzites is a fine-grained argillaceous slate, shading up into cal- 
careous shales, of the bottom of the Ute limestone. At the base of the 
latter were obtained — 

Dikellocephalus Wahsatchensis. 
Dikellocephalus gothicus. 
Crepicephalus (Loganellus) quadrans. 
Lingulepis Ella. 


Here the limestones generally are considerably thicker than in the sec- 
tion described in Ogden Canon. We estimate them at about 2,000 feet. 
From the upper part of the same series, a few miles south, at the head of 
Box Elder Canon, F’. H. Bradley, in 1871, obtained Halysites catenulata. In this 
immediate region, therefore, we have obtained Quebec forms near the base 
of the Ute limestone, and Bradley a form distinguishing the Niagara near the 
summit of the same member. 

East of Cache Valley synclinal lies a broad anticlinal, which 
diverges from the trend of the Wahsatch and strikes a little east of 
north. The character of this anticlinal is somewhat peculiar, showing a 
very gentle slope to the east and a much more considerable one to the 
west. Throughout the whole axial region of the anticlinal is a gently dip- 
ping series of the Cambrian quartzites, overlaid on both flanks by the out- 
wardly dipping Ute limestones. ‘To the east the series above that horizon is 
entirely covered by the Vermilion Creek Eocene Tertiary, while to the west the 


* United States Geological Survey of Montana, Idaho, Wyoming, and Utah, Hayden, 1872. 


PALHOZOIC EXPOSURES. 179 


exposures in Muddy Canon and Blacksmith’s Fork show the full section from 
deep in the Cambrian quartzite to the middle and higher members of the 
Wahsatch limestone. About eight miles to the north of Blacksmith’s Fork 
Canon the Cambrian quartzites appear with a gentle dip to the west, grad- 
ually flattening out to the east. Conformably overlying them, and itself 
conformably overlaid by the Ogden quartzite, is a fine and characteristic 
exposure of the limestone at Ute Peak, the typical locality from which this 
body of Silurian limestone has received its name. The peak is on the south 
side of Muddy Creek, just below the junction of its two important forks, the 
lofty and abrupt faces of Ute Peak itself forming a wall of the main canon 
and of the south fork. From the stream’s bed it has an elevation of 2,500 
feet of precipitous slope, while toward the west it falls away with the gentler 
inclination of the higher plateau country. The beds here strike from 15° to 
20° west of north, and dip westwardly from 15° to 20°. The relations of 
the Ute group with the underlying series are well shown. The canon of 
the south fork has cut through the base of the Silurian limestone, and also 
through the thin shales which form the uppermost member of the Cambrian, 
exposing in the bed of the canon the Cambrian quartzites, which gently rise 
to the east toward the axis of the anticlinal. The canon of the north fork 
of the Muddy, running at right angles to the strike, cuts through 1,600 
to 1,800 feet of the quartzite, forming a narrow, almost impassable gorge, 
with perpendicular walls. In these quartzites were observed some pecul- 
iar markings suggesting imperfect borings or the tracks of worms, such 
as have been ascribed to the genus Scolithus. The shales over the quartz- 
ites are indurated argillites, slightly calcareous and interlaminated with 
brown, earthy-colored sandstone, altogether making a group 100 feet in 
thickness. A Cambrian rock of interest occurs in Beaver Cafion. It is 
a peculiar smoky-purple quartzite, which is again seen on the east side of 
the Wahsatch, opposite Centreville. It is of remarkably vitreous lustre, and 
is a tough, dense rock. The individual grains of quartz, up to the size of a 
pea, have a peculiar purple dusky hue, the siliceous matrix being made up 
of an excessively fine eryptocrystalline, almost amorphous quartz, the beds 
developing a certain schistose structure from partly foliated quartz. Minute 


flakes of white mica, and fluid inclusions with moving bubbles, are detected 


180 SYSTEMATIC GEOLOGY. 


with the microscope. The Ute limestone is shown upon the slopes of Ute 
Peak to be very nearly 2,000 feet thick. Although there are numerous 
passages of pure limestone, the average character of the whole mass is 
siliceous, while the lower third or quarter is varied by a considerable 
amount of fine argillaceous material. Besides the general siliceous nature 
of the whole Ute group here, there are also beds of pure sand, and an immense 
amount of calciferous sand rock is intercalated at intervals throughout the 
whole mass. Some fine beds toward the middle of the series develop, on 
weathering, a remarkably banded structure, due to the variable amount of 
silica and the organic matter connected with the lime. Calcareous schists 
and sandy beds decidedly predominate over the pure lime beds. This 
siliceous character seems to be remarkably persistent over wide areas. 
About twenty-five feet above the top of the Cambrian argillites, in a bed of 
calcareous shale, enclosed in dark, dense limestones, are found numerous 
Entomostracea containing new species of two genera: 


Dikellocephalus quadraceps. 
Conocephalites subcoronatus. 


Two hundred feet higher in the series is a dark, siliceous limestone, some- 
what cherty, which outcrops on the north side of the peak, bearing an 
undetermined species of the genus Obolella, and near the summit of the 
series, about 200 or 250 feet below the bottom of the Ogden quartzite, were 


found — 
Euomphalus (Raphistoma) rotuliformis. 


Euomphalus (Raphistoma) trochiscus. 
Maclurea minima. 


On the summit of the ridge, but still somewhat below the Ogden quartzite, 


were found — 


Ophileta complanata. 
Raphistoma acuta. os 


These characteristic spaces prove that the greater part of the Ute limestone 
is Quebee. They leave a small portion of the top of the series unaccounted 
for, and it seems probable from the Halycites which was found near the 


PAL OZOIC EXPOSURES. 181 


summit of the series by Bradley, taken together with the Upper Silurian 
fossils from the upper part of the Silurian limestone in middle Nevada, that 
the extreme upper portion of the Ute limestone of the Wahsatch, say from 
150 to 200 feet, may be, and most probably is, of Upper Silurian age, while 
the remainder of the 2,000 feet is clearly Quebec. 

Box Elder Peak is the culminating point of the promontory-like north 
end of Wahsatch Range. The limestones that overlie the Ogden quartzite 
dip to the northeast from 45° to 50°. Well up in the series of limestones 
were obtained the following : 


Zaphrentis excentrica. 
Zaphrentis Stansbury. 
Cyathophyllum Nevadensis. 
Lithostrotion Whitneyr. 
Productus cora. 

Productus punctatus. 


Here are exposed about 4,000 feet, not far from two thirds of the entire 
Wahsatch limestone. 

Province oF THE GREAT Basty.—From the meridian of 112° to that 
of 120° extends the Great Basin country, which is characterized by broad 
valleys of Tertiary and Quaternary, interrupted by fragmentary outcrops 
of meridional ranges, which often reach a considerable height, and culmi- 
nate in Humboldt Range at a little over 12,000 feet above sea-level. The 
country immediately bordering the western base of the Wahsatch, whose 
lowest depression is occupied by Great Salt Lake, is at an elevation of 
about 4,200 feet. This nearly level basin extends westward about two 
degrees to the base of Ombe and Gosiute ranges. Thence for about seventy 
miles westward the average elevation of the Quaternary valleys rises, 
until at Ruby Valley it is about 6,000 feet. Still westward the valleys 
gradually decline to the level of Pyramid Lake, 3,900 feet in altitude. 
This whole region is ribbed with detached mountain ranges, rudely par- 
allel and generally of meridional trend; anticlinals, synclinals, and mon- 
oclinal masses which rise suddenly out of the Tertiary and Quater- 
nary plains. They are essentially composed of partial exposures of 


182 SYSTEMATIC GEOLOGY. 


Paleozoic rocks, together with unconformable underlying masses of Ar- 
chean granite and schist, the whole broken through and often masked by 
extensive flows of Tertiary volcanic rocks. This briefly characterizes the 
region as far as the meridian of 117° 15’, beyond which to the west no 
Paleozoic exposures are seen. From that meridian to the Sierra Ne- 
vada the main geological characteristics are frequent masses of Archean 
granite and schist and enormously thick developments of rocks of the 
Alpine Trias and Jurassic ages, together with great outbursts of volcanic 
rocks. The section of the Great Basin, therefore, which comes within 
our observation consists of a central mass in the region of Pinon and 
Humboldt ranges, longitude 115° 45’, where the valleys which skirt the 
mountain bases are about 6,000 feet high, and depressed regions flanking it 
to the east and west, one occupied by the basin of Great Salt Lake, and 
the other by the family of lakes which receive the drainage of Humboldt 
and Truckee rivers. The entire distance from the base of the Wahsatch, 
which bounds the basin on the east, to the flanks of the Sierra Nevada, 
which outline it on the west, is about 425 miles, while the extent of the 
region characterized by Paleozoic outcrops, namely, from the Wahsatch to 
the meridian of 117° 15’, is about 275 miles; and this is the province whose 
geological complexities I am about to attempt unravelling. In this 
region there are between twenty and thirty considerable mountain masses 
which rise out of the Quaternary and Tertiary plains, extend a short dis- 
tance, usually in a north-and-south or northeast-and-southwest trend, and 
then either abruptly or gradually decline beneath the level of the desert 
again. In no single one of these ranges is the whole Paleozoic section 
displayed, and, studied by itself, it would have been excessively difficult to 
establish a correct sequence for the various members. It is only when com- 
pared with the full conditions so splendidly displayed in the Weber section 
of the Wahsatch that we are at all able to decipher these isolated moun- 
tain blocks. With the exception of Humboldt and Pinon ranges, the con- 
tinuity of the strata is not very great. Since the whole Palzeozoic is made 
up of quartzites and limestones, in the absence of characteristic fossils it is 
sometimes impossible to refer a body of limestone finally. There are many 
instances where the whole mountain mass consists of a low exposure of 


PALM OZOIC EXPOSURES. 183 


limestones ot no very great thickness, characterized by Coal Measure 
invertebrates; the fossils offering insufficient evidence to warrant a defi- 
nite reference either to the Upper or the Lower Coal Measure limestones. 
In general, the Upper Coal Measure limestone, which in the provinces of 
the Wahsatch and Uinta was distinguished by the constant intercalation of 
sandy material throughout its upper horizons, in the province of the Basin 
is chiefly of limestone, and that often dark and heavily bedded, not litho- 
logically distinguishable from certain parts of the Wahsatch body ; so that 
when an isolated body of limestone is met with, whose exposed thick- 
ness is not too great to be stratigraphically referred to the Upper Coal 
Measures, and the fossils likewise do not show distinctly to which horizon 
it should be assigned, we have sometimes been obliged to make an arbi- 
trary reference simply from the probable connection of the body with 
neighboring ranges. When we find a body of from 5,000 to 7,000 feet of 
limestone underlaid by a quartzite and containing Coal Measure fossils in 
the upper members, we unhesitatingly refer it to the Wahsatch, and this 
reference has been further strengthened by the discovery, in the lower 
horizons of the body, of a considerable number of sub-Carboniferous and 
pure Devonian types, as well as the recurrence of the Waverly horizon, 
so well developed in the Wahsatch. On the other hand, as will be seen 
to be not infrequently the case, when a range consists of a body of lime- 
stone under 2,000 feet in thickness, resting upon the quartzite and carry- 
ing Coal Measure fossils down to the lowest limestone beds, we have felt 
entirely secure in referring it to the Upper Coal Measure series and Weber 
sandstone. In the case of a thick body of limestone carrying the well 
defined Devonian forms in its lowest members, and directly underlaid by 
a thin quartzite never exceeding 800 feet, we have recognized it as the 
bottom of the Wahsatch and the Ogden quartzite. Again, a thin quartzite 
is seen in some localities capping a body of dark siliceous limestone which 
carries in its summit members lower Helderberg fossils, and in that case 
the quartzite was considered to be identical with the Ogden Devonian. 
No forms at all equivalent to the Permo-Carboniferous fossils have been 
found, and no rocks at all similar to the shales which enclose them in the 
Wahsatch have been seen anywhere in our section of the | Great Basin. 


184 SYSTEMATIC GEOLOGY. 


While the Wahsatch section illustrates in its completeness the whole strati- 
graphical sequence of Paleozoic rocks, paleontological proofs are only 
furnished in that range from the summit of the Permo-Carboniferous down 
to the base of the Quebec, at which horizon the fossils collected at Call’s 
Fort, directly above the Cambrian shales, mark the lowest depth from 
which organic forms were obtained. In the-Great Basin the lower rocks— 
Quebee limestone, and shales and quartzites of the Upper Cambrian— 
are well developed, and here with a stratigraphical sequence equiva- 
lent to that of the Wahsatch we find abundance of Primordial forms. 
Therefore, in establishing the complete scheme of the Palzeozoic series, 
while the Wahsatch furnishes everything but Cambrian life, that life is 
furnished in the desert ranges in a series which are the undoubted equiva- 
lents of the basal rocks of the Wahsatch. With these two the section is 
rendered complete, and is based upon evidence which may be considered to 
give it a final value. Since the great Paleozoic feature of Wahsatch Range 
is its remarkable display of continuous sections, in treating of that province 
I have done little more than describe and fortify these sections. The prov- 
ince of the Great Basin, on the other hand, is one in which the individual 
sections are very slight and too innumerable for re-description here. They 
will be found in Chapters III. and IV., and part of Chapter V., of Volume 
II. Since the interesting Paleozoic feature of the Great Basin, so far as it 
applies to this chapter, is the continuance westward of the series as dis- 
played in the Wahsatch, I conceive that the best method of treatment here 
is to begin with the lowest strata, and describe the occurrence of each 


t 
member in ascending. JI commence, therefore, with the 


CAMBRIAN AND SILURIAN. 

Passing over the limited display of quartzites underneath the trachytes 
of the Traverse Mountains, which from lithological evidence alone have 
been referred to quartzites of the Cambrian, the first occurrence which 
merits attention is in Oquirrh Range. By an interesting series of 
faults near the western edge of this body, in the immediate vicinity 
of Ophir Canon, the Cambrian quartzites and the thin bed of argillites 
so often mentioned as capping the series are displaced and brought up 
to view amidst masses of Wahsatch limestone which form the quaqua- 


PALAOZOIC EXPOSURES. 185 


versal uplift of this region. About one eighth of a mile north of Ophir 
City is a straight, sheer wall of quartzite 300 or 400 feet high. The 
material of these siliceous rocks is the reddish salmon quartz that forms the 
uppermost part of the great body of Cambrian quartzites in the Wahsatch. 
Over these are about 100 feet of greenish-yellow clays, the equivalent of 
the argillites of Call’s Fort and the Cottonwood region, which contain the 
following forms, equivalent to those collected at Call’s Fort and represent- 


ing the horizon of contact between the Primordial and the Quebec—a hori- 


zon in Utah always confined to these shales: 


Ogygia producta. 
Ogygia parabola. 
Ogygia n. sp. 
Lingulepis n. sp. 
Kutorgina n. sp. 
Dikellocephalus sp.? 
Dikellocephalus sp.? 


The relation of this exposure to the overlying parts of the series is 
obscure. The next fossils found in the limestones above are of the Wa- 
verly horizon, which Mr. Emmons, who has examined the region, be- 
lieves to have been faulted down into contact with these Quebec shales. 
The chief value of this locality, aside from its relations with the rock above, 
is in confirming the reference to the Quebec age of the upper part of these 
shales and fixing the bottom of the Silurian. 

The western slope of Aqui Range, from Skull Valley up to Bonne- 
ville Peak, is formed of a continuous exposure of quartzites, making in 
all a thickness of about 6,000 feet, which have an average dip of 25° 
to the west, and decline to a much less steep position at Bonneville 
Peak. The prevailing rock is white and yellowish-white quartzites, 
with occasional conglomerate beds and limited strata of dark-green argil- 
lites containing spangles of muscovite on the surface-planes. There is 
also a dusky purple quartzite with pellucid pebbles, such as have been 
described from Blacksmith’s Fork and the Wahsatch of the Farming- 
ton region. The fact of so extended a series of quartzites underlying 


186 SYSTEMATIC GEOLOGY. 


5,000 or 6,000 feet of limestone is strong evidence in favor of assigning 
this to the Cambrian. The same quartzite stretches northward along the 
western side of Aqui Range, up to Grantville Peak, which is the crest of 
an abrupt anticlinal whose western member dips only about 45°, while 
the eastern approaches a horizontal position. The exposures at both 
places are very fine. At Bonneville Peak, particularly, the eastern base 
presents an almost perpendicular wall 2,000 or 3,000 feet in height. The 
characteristic feature of the beds on the saddle north of Grantville Peak is 
the occurrence of the flattened and distorted pebbles of the conglomerate 
already described in Ogden Canon. In the Schell Creek Mountains, which 
form the eastern boundary of Steptoe Valley, south of the great flow of 
rhyolite that overwhelms nearly all the sedimentary rocks in the northern 
part of the range, at a locality somewhat south of the limits of our map, 
are seen the heavy quartzites of the Cambrian, and directly over them 
argillaceous and calcareous shales from which were obtained Crepicephalus 
(Loganellus) amytus and Lingulepis Mera. This, from its position, capping 
the great Cambrian quartzite, and containing undoubted Cambrian forms, 
shows that the dividing-plane between the Cambrian and the Quebec is for 
this region in the thin shales. Farther westward a great limestone body 
takes the place of the upper Cambrian quartzite and the shales. 

In the high ridge east of Egan Canon is displayed a section of Cam- 
brian rocks resting unconformably upon the granite and overlaid by heavy 
bodies of limestone. Between the Cambrian and the continuous outerops 
of limestone is a region variably covered with soil and characterized by 
infrequence of outcrops. There is ample room for Ute limestone and 
Ogden quartzite, though their presence is not proved. Here, directly 
over the granite, are several thousand feet of quartzitic schists, capped 
by about fifty feet of highly laminated fissile argillites. The character 
of the quartzites is quite similar to that of the quartzitic schists of the 
Wahsatch. It is compact, often semi-transparent, frequently quite vitreous, 
and shows occasional traces of granular structure. Certain beds of dark 
purple quartzite carry coarse quartz pebbles, others contain flakes of mus- 
covite, and still others show a considerable development of bronze-colored 
phlogopite. All the outcrops noted as coming to the surface through the 


PALHOZOIC EXPOSURES. 187 


soil and débris which overlie this Cambrian series show the conformable 
dip of the limestones to the west. 

In White Pine Range, the base of Pogonip Ridge at its northern end, 
shows certain limited outcrops of granite, upon which are only partially 
exposed bodies of mica schists and black arenaceous and argillaceous shales, 
overlaid by an undetermined thickness of compact, vitreous, steel-gray 
quartzites, identical with the Cambrian quartzites hereafter to be described 
in the Pinon. Their position shows an eastward dip of from 24° to 30°. 
Rising a little on the range, they are conformably overlaid, although the 
contact is débris-covered, by a great thickness of dark limestone. The 
lower limestone beds are highly siliceous, of a steely-black, with blue 
shades, and varying a good deal in physical characteristics, passing down- 
ward into rather argillaceous, calcareous shales. Higher in the series it 
develops a dark-blue color, and is seen to be much banded by zones of 
arenaceous limestone and occasional seams of pure chert several inches 
thick. The entire limestone zone is about 4,000 feet thick. From these 
dark heavy beds were obtained the following fossils, determined by Hall 
and Whitfield: 


Crepicephalus (Loganellus) Hague, n. sp. 
Crepicephalus (Bathyurus) angulatus, n. sp. 
Crepicephalus (Loganellus) sp. undeterminable. 
Crepicephalus (Loganellus) sp. undetermined, 
Conocephalites (Pterocephalus) laticeps, n. sp. 
Dikellocephalus flabellifer, n. sp. 
Dikellocephalus quadriceps, n. sp. 

Ptychaspis pustulosus, n. sp. 

Ptychaspis n. sp. undescribed. 
Charicocephalus tumifrons, n. sp. 

Agnostus communis, n. sp. 

Lingulepis Mera. 

Obolella sp. undetermined. 


These clearly Primordial forms extend up for 2,000 feet into the body 
of limestone. This is the first indication of an important change between 


188 SYSTEMATIC GEOLOGY. 


the lower Palzeozoic horizons of the Basin and the Wahsatch. We saw that 
at Call’s Fort, on the western base of the Wahsatch, Quebec forms, although 
representing the very base of the Quebec and closely allied to the Primor- 
dial species, were found at the base, or very near the base, of the Ute lime- 
stone, the lowest limestone of the whole series; and again that Quebec fossils 
were found within twenty-five feet of the base of the Ute limestone at Ute 
Peak by the forks of the Muddy. The thin calcareous and argillaceous 
zone which rests upon the top of the quartzites has here given place to cal- 
careous sediment expanded to a thickness of 2,000 feet, and merged itself 
into the Ute limestone. This limestone from the typical locality at Pog- 
onip Ridge is called the Pogonip limestone, although the upper 2,000 feet 
are in reality the equivalent of Ute limestone. Near the top of the series, 
above the horizon from which the foregoing Primordial fossils were obtained, 
the following Quebec species were collected: 


Ptychaspis pustulosus, n. sp. 
Bathyurus Pogonipensis, ni. sp. 
Orthis Pogonipensis, n. sp. 
Strophomena Nemia, n. sp. 
Porambonites obscurus, n. sp. 
Raphistoma acuta, n. sp. 
Cyrtolites sinuatus, n. sp. 


Above these Quebec members of the limestone series of this locality 
there is a gap occupied by a valley deeply covered with soil, and neither 
of the uppermost members of the limestone series is seen, nor their contact 
with the rocks above. All that this locality develops are the Cambrian quartz- 
ites and schists overlaid by a body of at least 2,000 feet of Primordial lime- 
stone, which passes up without petrological change into beds of similar 
limestone characterized by distinct Quebec forms, and the upper continu- 
ance of the limetones is unknown. 

At the Eureka Mining District, which is in the body of hills that con- 
nect Diamond and Pinon ranges, south of Diamond Valley, and a little 
south of the south line of our map, there is an excellent exposure of the 
Pogonip limestone with the underlying Cambrian schists and quartzites 


PALMOZOIC EXPOSURES. 189 


The ridge of Prospect Mountain shows the same lithological features as 
those of Pogonip Ridge, and carries through an enormous thickness of the 
formation, certainly 2,500 feet, Primordial forms, embracing the following: 


Crepicephalus (Loganellus) granulosus. 
Crepicephalus (Loganellus) maculosus. 
Crepicephalus (Loganellus) nitidus. 
Crepicephalus (Loganellus) simulator. 
Crepicephalus (Loganellus) unisulcatus. 
Dikellocephalus bilobatus. 
Dikellocephalus multicinctus. 

Agnostus Neon. 

Agnostus prolongus. 

Agnostus tumidosus. 

Lingulepis Mera. 

Lingulepis minuta. 

Obolella discoida. 

Kutorgina minutissima. 

Leptena melita. 


Owing to great disturbance and alteration of the limestones, few 
fossils were obtained from the upper 1,800 feet of the Pogonip belt; but 
an Orthis Pogonipensis and a Bathyurus, probably Pogonipensis, were col- 
lected—enough to prove the occurrence of the Quebec, and thus establish 
the complete parallelism of horizons with the great Pogonip limestone at 
White Pine. The Eureka locality, however, is of great geological interest, 
since conformably over the Pogonip is the Ogden quartzite admirably 
defined, having a width of about 900 feet, and still conformably over that 
again the immense Wahsatch limestone. Under the Pogonip are con- 
formable quartzites of the Cambrian, which, however, were not critically 
studied. 

The northern end of that portion of Pinon Range which lies south of 
Humboldt River culminates at the high point of Raven’s Nest Peak. Here 
is a fine exhibition of the Cambrian quartzites and schists, with a perfect 
exposure of their passage upward into the Pogonip limestone, although the 


190 SYSTEMATIC GEOLOGY. 


limestones here have so far failed to yield any fossils. But from evidence 
of the overlying Ogden quartzite and the Devonian base of the Wahsatch 
limestones, which are characterized by numerous well defined Upper Held- 
erberg species, the heavy body of limestone colored as Silurian could not 
be mistaken for Wahsatch limestone, of which only the lower or Devonian 
portion is here seen. Pinto Peak, a high tabular quartzite mountain, lies in 
the axis of an anticlinal, the rocks both to the east and west dipping in con- 
trary directions, and the whole curve of the anticlinal being clearly seen to 
the south, where the Devonian quartzite and limestones arch continuously 
over and form the summit of the ridge. The Cambrian quartzites, as shown 
at Pinto Peak and at the base of Raven’s Nest Peak, are heavily bedded 
quartzitic schists, carrying some beds which are highly micaceous, and at 
the top characterized by occasional thin beds of argillaceous material. The 
higher quartzites are steel-gray, rather saccharoidal in texture, are slightly 
calcareous, and superficially resemble the steel-gray limestones above them. 
For a considerable distance in the upper quartzite zone, say 300 or 400 feet 
below the contact with the Pogonip, there is not a little calcareous material, 
the analysis yielding only 76 to 78 per cent of silica, the remainder being 
carbonate of lime. It is a highly crystalline calcareous quartzite, and passes 
upward into rather siliceous limestones, which are alternately dark and light. 
Doubtless if the steep slope of Raven’s Nest Peak were given a more careful 
examination than our time permitted, Primordial and Quebec fossils would 
be found. The whole limestone cannot be less than 4,000 feet in thickness, 
and by its volume and position conformably between the Ogden quartzite and 
the basal quartzites can be nothing but the Pogonip. The strike of the lime- 
stones of Raven’s Nest Peak is diagonally across the range at about north 
25° east, and they dip from 25° to 35° northwest. Directly south of Dixie 
Pass the ends of the strata are abruptly cut off by a fault and very deep dislo- 
cation, and their edges are abrupt and partly masked by an immense overflow 
of trachyte. The upper members directly under the Ogden quartzite are 
less siliceous than the beds below, a good deal altered, more highly crystal- 
line thar the lower strata, and reticulated with innumerable seams of white 
calcite. The quartzites and schists underneath this body of limestone are 
exposed downward for not less than 5,000 feet. The conformity between 


PALZOZOIC EXPOSURES. 191 


the deep Cambrian quartzitic schists and the Ute-Pogonip limestone is abso- 
lutely perfect, as is the contact between the upper members of the Ute- 
Pogonip and the overlying Ogden. In reference to the line here separating 
the Cambrian and the Silurian—which is intended to be so drawn as to 
it should be 
said that there is an error on the geological map at this point. The line as 


include the Primordial in the Cambrian, as fixed by Dana 


drawn here represents the junction of the steel-colored limestones with the 
underlying steel-colored quartzites. It should be carried 1,600 or 1,806 
feet higher, which would have the effect of narrowing the Silurian band on 
the map and widening the Cambrian. Not enough study was given to this 
region to prove clearly that the lowermost rocks exposed here are not Ar- 
chan. There are some gneissoid rocks which differ lithologically from any 
of the known Cambrian beds, but they were not sufficiently observed to 
determine their conformity or nonconformity with the quartzites above. 
Farther south in this range, near Mineral Hill, the Ogden quartzite is well 
developed about 800 feet in thickness; and conformably underlying it, 
especially as displayed upon Cave Creek, about three miles south of 
Mineral Hill, is the top of a body of limestone more or less siliceous, 
which, from its position under the Ogden, is also referred to the top of 
the Ute-Pogonip body. The only organic remains found in this devel- 
opment of limestones are some stems of corals, which, however, are of 
special interest, as Whitfield determines them to be of the Lower Helder- 
berg horizon. 

West of Pinon Range and south of Garden Valley, in the Roberts Peak 
Mountains, appears a high mass of limestone, flanked on both sides by 
quartzites, which have been referred to the Ogden. About 3,000 feet of 
conformable limestones are displayed here, which lithologically repeat the 
features of Pogonip Ridge. These are dark, more or less siliceous, and 
intercalated with calcareous shales and thin, cherty beds. ‘The strata incline 
to the east with a varying strike of northwest-southeast. Along the northern 
slopes the observed dip was 40° or 50°, here striking north 20° west, while 
the southeasterly foot-hills gave a dip of but 18° to 24° to the east, and a 
strike more nearly due north. The upper horizons on both the north 
and south slopes yield fossils ranging from the Upper members of 


192 SYSTEMATIC GEOLOGY 


the Quebec to the Lower Helderberg, the collection including the fol- 


lowing: 
Cladopora sp 2? (resembles C. seriata) 


Orthis sp.? (resembles O. hybrida). 

Atrypa reticularis. 

Atrypa sp.? (resembles A. nodostriata). 

Ehynchonella sp.? 

Illenus sp.? 
All of these but the Rhynchonella have been ascribed by Hall and Whitfield 
to the Niagara; while the Rhynchonella, which was collected farther up, 
closely resembles the Rhynchonella found at White’s Ranch, associated with 
Lower Helderberg forms. 

North of the Humboldt, in Boulder Creek Valley, near the intersec- 
tion of the 41st parallel with the meridian of 116° 30’, at a place called 
White’s Ranch, is an isolated hill of limestone conformably overlaid by a 
pure, greenish-white quartzite having all the characteristics of the Ogden. 
The outcrop, as will be seen upon the map, is limited on all sides by the 
Quaternary of the valley. It is an absolutely isolated hill. The limestones 
were rather dark, fine-grained, and decidedly siliceous, the beds, for the 
most part, thin and intersected with siliceous seams, the latter carrying 
some branching impressions like rootlets. There is a total thickness of 
about 600 feet of limestones. From these were obtained, in the neighbor- 
hood of the overlying quartzite, the following Lower Helderberg association 
of forms: 

Atrypa reticularis. 

Pentamerus galeatus. 

Strophodonta sp.? (like S. punctilifera). 
Orthis sp.? 

Trematopora. 

Celospira. 

Rhynchonella. 

Favosites (sp. allied to F’. Helderbergia). 
Diphyphyllum n. sp. 

Campophyllum. 


PALZOZOIC EXPOSURES. 193 


This establishes the fact that the uppermost horizon of the Ute-Pogonip 
limestone body is distinctly Lower Helderberg. Roberts Peak, Eureka, 
and White Pine form a region along a meridional belt extending north- 
and-south for seventy miles, by a breadth of about thirty miles, exposing 
the entire development of Silurian and a part of the Cambrian series. The 
whole 4,000 feet of limestone consists of three distinct members: 1, the 
lower 2,000 feet of Primordial; 2, a restricted but as yet unknown amount 
of the middle of the series, being Quebec; 3, a considerable breadth of 
Niagara overlying that, with the summit members (underlying the Ogden 
quartzite) of the Lower Helderberg. 'The line, therefore, which separates 
the Primordial, or Cambrian, from the Silurian, will in this region come 
near the middle of the Ute-Pogonip limestone. 

Ocpen Quartzite.—Humboldt Range, by far the most considerable 
mountain ridge in central Nevada, consists essentially of a long body 
of Archean granitoid gneisses and quartzites, unconformably upon which 
rest strata of the Wahsatch limestone dipping to the east and west, show- 
ing the range to have been an anticlinal which was folded with its axis 
running approximately in the line of the old Archean body. The few 
exposures of the westerly dipping rocks have their plane of contact in the 
horizon of the Wahsatch limestone, the Ogden being altogether buried; 
but south of Frémont’s Pass the whole body of the ridge is formed of east- 
erly dipping strata, 7,000 feet of the Wahsatch limestone underlaid by the 
quartzites of the Ogden. From Frémont’s Pass to Hastings’s Pass the ex- 
treme western foot-hills are made up of easterly dipping quartzites, having 
a close physical resemblance to the Ogden beds of the Pinon. Their hori- 
zon is determined by their lying conformably at the base of the Wahsatch 
group. 

Above the Ute-Pogonip limestone of Raven’s Nest Peak, Pifion Range, 
and quite conformable with it, lies a body of quartzite 900 to 1,100 feet in 
thickness. It is of thin, even lamination toward the lower members, and 
above of rather heavily bedded quartzites, much stained with iron. ‘The 
material of the rock is extremely fine. It contains no conglomerate, as far 
as observed, and no coarse, angular, or gritty grains, and shows throughout 
an extremely fine suberystalline texture. It is traversed by many jointing- 

13 kK 


194 SYSTEMATIC GEOLOGY. 


planes striking northwest-and-southeast, or nearly at right angles to the 
strike of the rock. From the Raven’s Nest region it trends southwest 
and then curves again to the southeast, skirting the great body of Ute- 
Pogonip limestone, and about five miles south of Pinto Peak forms the 
crest of the main anticlinal of the range. ‘Toward the southwest, the west- 
ern side of the anticlinal is seen dipping under the lower members of 
the Wahsatch limestone. At Pinon Pass the outcrops are very distinct, 
and toward the west they pass gradually beneath Devonian limestones. 
These limestones form here a synclinal whose axis is northwesterly, and 
rapidly curve up again with an easterly dip, the Ogden quartzite reappear- 
ing at the western base of the range In other words, from Pinto Pass it 
curves under the anticlinal, and reappears between the Silurian limestone 
of Cave Creek and the overlying Devonian limestone. Here, where it is 
distinctly outlined by the limestones on both sides, it is about 800 feet 
thick, while north, in the region of Raven’s Nest, it is 900 to 1,100 feet. 
The exposure in the region of Pony Creek, where the Ogden quartzites 
arch over and form the cap of the anticlinal, is exceedingly fine, bold 
hills having been eroded out of the arch. The lithological characteristics 
of this quartzite throughout the Pinon are similar, except perhaps along 
the western base, where it has a rather more flinty and vitreous aspect. 
The quartzite which overlies the Silurian limestone of Roberts Peak is 
rather obscure, and its contact with the underlying rocks is not shown; so 
that, while it is probably Ogden, the proof is uncertain. 

At the small isolated hill which rises to the surface through the 
Quaternary of Boulder Creek on the line of the 41st parallel, near the 
meridian of 116° 30’, a body of quartzites has already been described as 
conformably overlying the limestones which carry Lower Helderberg fossils. 
This, from its position directly over the top of the Ute limestone, is assigned 
to the Ogden. 

At White Pine, where are exposed both Pogonip and Wahsatch lime- 
stones, there is a gap between the two great bodies—a valley covered 
with Quaternary débris, in which are seen no outcrops. The whole region, 
which should be covered by the Ogden quartzite, is masked by detritus 
and earth, so that its presence or absence at that locality is so far not proven. 


PALMHOZOIC EXPOSURES. 195 


From the undoubted equivalence of the two bodies of limestone to those 
exposed in the Pinon, and from their relative dip here, there is little doubt 
that the Ogden does occur underneath the valley earth. As already noted, 
it recurs in Eureka District in its proper place in the series. 

Excepting Aqui and Oquirrh ranges, wherever the Ute and the 
Wahsatch limestone are both exposed, the Ogden is clearly seen. In the 
Aqui the examination was exceedingly hasty, and the region is complicated 
by faults, so that its not having been seen is no proof of its absence. On 
the contrary, we believe it to be there, and have so stated on the map. 

In the region of Ophir City, in Oquirrh Range, the Ogden is wanting. 
At that locality is found a small gap between the fossils which represent 
the Call’s Fort horizon and the Waverly group. In other words, both the 
Ute limestone and the Ogden quartzite appear to be wanting; but we con- 
ceive this to be wholly due to complication resulting from faults. Except- 
ing in these two obscure localities, wherever we have found a section which 
has exposed both Silurian and Carboniferous beds, the Ute limestone and 
overlying Ogden quartzite are invariably recognized, and we consider them 
to be, so far as the Fortieth Parallel region is concerned, of remarkable 
stratigraphical persistence. 

At one place in Frémont’s Pass, Humboldt Range, nonconformable 
contact between the Ogden quartzite and the underlying Archzean may be 
observed. Otherwise, wherever the Ogden is seen west of the Wahsatch, 
either the base is not visible or else it is found resting upon the Ute- 
Pogonip limestone. Limited, then, by the Lower Helderberg fossils below 
and the Upper Helderberg fossils above, and itself yielding no organic forms, 
it may be taken, until still further restricted, to represent the Oriskany, 
Cauda-galli, and Schoharie horizons; and since the Lower Helderberg fossils 
possess so high a facies, I have considered it right to classify the Ogden 
quartzite altogether as Devonian. It is not at all impossible that future 
study may discover sufficient evidence to settle this question finally. Until 
then, it seems to me, on the whole, most likely to be chiefly Devonian, 
and it is therefore so placed in our series. 

Wausatcu Limestone.—North of Salt Lake is a considerable area of 
limestones, which begin on the west side of Malade Valley, on the northern 


196 SYSTEMATIC GEOLOGY. 


limits of our map, and extend south and west, dipping under Hansel 
Spring Valley, and then extending still farther southward to form the 
greater part of Promontory Range. This region shows several synclinal 
and anticlinal folds, with very gentle dips, but exposes no great thickness of 
limestones except in the higher part of the Promontory itself. Southwest of 
the railroad are large bodies of limestone, of prevailing gray color, the 
lower exposures inclined to dark, almost black beds. The rocks dip at an 
angle of 38° westward. Extending down the range, they are subject to 
interesting structural disturbances, and in general expose about 3,800 or 
4,000 feet of thickness. Somewhere about 1,200 feet below the top of the 
series is an included zone of yellowish-brown sandstone, decidedly calcare- 
ous, intercalated with numerous thin sheets of gray limestone. The lower 
portion is sharply defined against underlying beds of dark-blue limestone, 
but on the upper limit, 300 feet up, it passes gradually through shaly 
beds into the limestone above. The general strike here is north 28° east. 
From the limestones directly below and directly above this siliceous zone, 
not far from Antelope Springs, were obtained the following : 


Productus prattenianus. 
Spirifer opimus. 

Athyris subtilita. 
Streptorhynchus (fragments). 


While farther south in the range, from limestones of the lower horizon, 
were obtained many Zaphrentis Stansburyi and Productus semireticulatus. It 
is assumed that this siliceous zone is equivalent to that described in the 
Weber section not far from the summit of the series. From the lithological 
character of the limestones themselves, as well as from the great thickness 
exposed and the facies of the fossils, this series is referred to the Wahsatch 
limestone, although neither the underlying nor the overlying quartzite 
occurs here at all. 

Considering this line of upheaval in its southern extension, it is evi- 
dent that I'rémont and Antelope islands are only parts of an Archean 
body which bears to this line of upheaval the same relation as does the Ar- 


cheean of the Wahsatch to that range. Southward on the same line are seen 


PALASOZOIC EXPOSURES. 197 


the Paleozoic masses of the Oquirrh and Pelican Hills. Within our map 
the Pelican Hills present only an unimportant mountain mass, made up of 
thinly bedded blue limestones with frequently intercalated quartzites, un- 
doubtedly referable to the uppermost region of the Wahsatch limestone as 
displayed upon the top of Tim-pan-o-gos. A few imperfect spirifers and 
crinoids were the only fossils found. 

The Oquirrh Mountains, on the other hand, offer an important ex- 
posure of the Palzeozoic series, thrown into complicated structural rela- 
tions, and about half made up of Wahsatch limestone, the remainder 
being overlying Uinta quartzite. The peaks rise to a height of 6,000 
feet above the plains, and offer splendid exposures. As seen at Dry 
Canon, the uppermost fossils of the Wahsatch limestone are of sub-Carbo- 
niferous types, and the vertical range through which fossils of this horizon 
and of the Waverly extend, is apparently greater than at any other point 
where the Wahsatch limestone is displayed. Since there is a structural 
obscurity about the bottom of the limestone, the exact height in the series 
at which the Waverly fossils are found is not known. From the westerly 
dipping beds near the mouth of Dry Canon were obtained — 


Streptorhynchus inflatus. 
Strophomena rhomboidalis 
Spirifer Albapinensis. 
Spirifer centronatus. 

- Rhynchonella pustulosa. 
Euomphalus Utahensis. 
Euomphalus Ophirensis. 
Michelina sp.? 
Zaphrentis sp.? 


In addition to these, from a ridge above and between Dry and East 
canons, in a fine-grained, dark limestone, Professor Clayton obtained some 
of these species, and— 

Proétus peroccidens. 

Orthis resupinata. 

Luomphalus latus, var. laxus. 


198 SYSTEMATIC GEOLOGY. 


Twelve hundred feet higher stratigraphically, Professor Clayton found — 


Trematopora. 
Fenestella. 
Polypora. 


And still higher geologically — 


Productus levicostus. 

Productus elegans. 

Productus semireticulatus. 

Productus Flemingi, var. Burlingtonensis. 
Spirifer striatus. 

Spirifer setiger. 

Spirifer Leidyi. 

Athyris subquadrata. 


From the head of Ophir canon, near the divide, were obtained — 


Streptorhynchus robusta. 
Chonetes granulifera. 
Spirifer opimus. 
Rhynchonella Osagensis. 


The crest of the range, between East Canton and North Cafion, shows 
the remarkable intercalations of quartzites and limestones of the Tim-pan- 
o-gos horizon, abounding in casts of Productus prattenianus and Spirifer 
opimus. Although the upper limit of the Wahsatch body is here defined 
by the Weber quartzite above the Tim-pan-o-gos horizon, the bottom is 
nowhere definitely shown. It is needless to amplify localities of the sub- 
Carboniferous or Waverly fossils in the Oquirrh. Suffice it to say that the 
whole condition described in the Wahsatch—the intercalations of the Tim- 
pan-o-gos horizon with their characteristic forms, the 5,000 feet of varied 
Coal Measure forms down to the sub-Carboniferous, and the occurrence of 
the Waverly level—is here thoroughly displayed. So also are the persist- 
ent siliceous zones which are near the upper part of the series, but still 
below the intercalated Tim-pan-o-gos level. Near Black Rock, enclosed 
in limestones carrying Productus semireticulatus, Productus prattenianus, 


PALAZOZOIC EXPOSURES. 199 


Streptorhynchus crenistrea, Spirifer opimus, Fenestella, Polypora, and Trema- 
topora, is a peculiar bed of white sandstone made up of rounded grains of 
limpid quartz differing entirely from the ordinary vitreous beds which are 
the characteristic intercalations of the Wahsatch. From the very north- 
western foot-hills of the range were obtained — 


Chonetes granulifera. 
Productus Nebrascensis. 
Productus longispinus. 
Martinea lineata. 
Athyris subtilita. 


A feature of the Wahsatch limestone not recognized by us in Wah- 
satch Range is the occurrence of beds of black, waxy shales, which are 
found at one or two horizons: one a small development just below the 
Waverly horizon, which may possibly correspond to the Devonian shales 
of White Pine; another appearing at the horizon of the Mono Mine, higher 
in the series. These shales are made up of black magnesian clay of ex- 
cessive fineness, which is also strongly charged with limy material. 

Upon Aqui Range is seen a long, continuous outcrop of heavy beds of 
limestone, extending from the northern extremity of the range to the south- 
ern limit of our map. From its thickness and physical character this has 
been referred to the Wahsatch, although the only recognizable fossil is a 
Zaphrentis multilamella. 

Stansbury Island isa sharp, steep anticlinal of dark limestones, dipping 
about 75° both east and west, with a north-and-south strike. The lime- 
stones are rich in Zaphrentis Stansburyi and Euomphalus subplanus. Along 
the eastern base of the island are considerable bodies of quartzite, conform- 
ably overlying the limestones, but themselves much obscured by soil. They 
have been referred to the Weber from their extent, but may possibly 
represent the siliceous beds of the Tim-pan-o-gos horizon. Bordering Great 
Salt Lake along the western side, and outcropping here and there through 
the Quaternary and Lower Quaternary beds of the desert, are isolated 
rocky hills, often rising to a considerable height, and for the most part com- 


posed of beds of dark, more or less siliceous limestone, capped in places by 


200 SYSTEMATIC GEOLOGY. 


bodies of quartzite and somewhat masked by Tertiary voleanie rocks. Car- 
rington, Hat, Dolphin, and Gunnison’s islands, Strong’s Knob, and the Lake- 
side Mountains, with four insular masses to the west and two considerable 
bodies of the Rocky Hills, together with Cedar Mountain and the little lime- 
stone buttes to the west, are all referred by us, from such scanty evidence 
as we could obtain, to the Wahsatch limestone. They are in general dark 
siliceous limestones, carrying Coal Measure fossils, usually of the species 
which predominate in the Wahsatch. The evidence on which they are re- 
ferred will be found in Volume II. For our present purposes they are only 
of value as indicating the continuity of the sheet to the west. Both the 
Ibenpah Mountains and the high ridge of Gosiute Range, culminating in 
Lookout Peak, a summit reaching 9,695 feet, display large masses of Wah- 
satch limestone. At the latter locality are shown fully 4,000 feet of dark 
limestone series. Highly altered specimens of Productus, not specifically 
recognizable, associated with crinoid stems, were the only organic remains 
found. 

At the south end of Peoquop Range and its connected body which 
culminates in Spruce Mountain, is seen a great area of varied limestones, 
for the most part dark-blue and dark-grayish-blue, and containing several 
interealations of siliceous and earthy impurities. Near the summit of 
Spruce Mountain were obtained — 


Productus costatus. 
Productus semireticulatus. 
Productus Nebrascensis. 
Eumetria punctilifera. 


From the ridge directly north of the peak and from several other localities 
were obtained Productus Nebrascensis and Fusilina cylindrica, together with 
large crinoid stems, pentangular disks, and the delicate form of an undeter- 
mined Trematopora. From several localities of the lower Peoquop to the 
east of Spruce Mountain were collected Athyris subtilita and Fusilina 
cylindrica. 

Here in the Peoquop are certainly between 3,000 and 4,000 feet of 


these heavily bedded limestones containing Coal Measure fossils, but the 


PALZOZOIO EXPOSURES. 201 


series is nowhere deeply enough exposed to arrive at the Devonian beds, 
nor high enough to show the overlying Weber quartzites. 

North of the Humboldt, in Tucubits Range, Wahsatch limestone is 
developed on a line extending from Tulasco Peak northwesterly for about 
twenty-five miles, and in topographical breadth the belt varies from three to 
four miles. The crest of Tucubits Range is formed of heavy masses of 
quartzite, referred to the Weber. Beneath these the dark limestones are 
particularly well exposed in Emigrant Canon and all along the western base 
of the range, especially at the South Fork of Forellen Creek. The beds 
have a gentle dip of 20° to 25° northward, while they strike a little west of 
the trend of the range, and consequently lower and lower limestones are ex- 
posed in passing southward. Near the mouth of Emigrant Cafion the beds 
stand at a steep angle, in some cases as high as 45° or 50°, and show ample 
evidence of local faulting. In a little ravine entering Emigrant Canon from 
the south is evidence of a northwest-and-southeast fault, of which the up- 
throw has been upon the eastern side, the eastern beds bending down steeply 
at the faulting-plane. A short distance above this, and east of the fault, at 
a point very near the base of the limestone, are exposed beds of calcareous 

shales several hundred feet thick. Above these are 300 feet of light-gray 
limestone, overlaid by 100 feet of yellowish calcareous shales, and above 
these 100 feet of black, thinly laminated, calcareous shales abounding in 
fossils; above these again 200 feet of dark-gray limestone, followed by the 
ordinary heavily bedded blue limestone for 1,500 or 1,600 feet. From the 
black shales above mentioned were obtained the following fossils of the 
Upper Helderberg horizon : 
Orthis multistriata. 
Orthis n. sp. 
Spirifer Vanuxemi. 
Atrypa reticularis. 
Cryptonella (fragment). 
Crania sp.? 

The cation slopes above this point are in general too much covered 

with detritus to afford continuous sections, but from the frequent intervals 


of limestone outcrops, and the absence of all others, it is clear that there 


202 SYSTEMATIC GEOLOGY. 


~ are 4,000 or 5,000 feet of consecutive beds showing toward the upper 
part a high proportion of shales, which are generally of light colors. Near 
the upper limits of the cafion is an outcrop of 500 feet of calcareous shales, 
weathering very yellow, and overlaid by light-drab limestones which pass 
into blue and siliceous limestones, carrying seams of calcite and crystals of 
pyrites. Conformably above, although the contact is obscured by soil, are 
seen heavy masses of Weber quartzite, which extend eastward and compose 
the whole summit and eastern slopes of the range. At the southern edge of 
the belt, at Tulasco Peak, in a little ravine running northwest from the 
summit, were obtained several Coal Measure fossils, among which were the 


following: 
Spirifer cameratus. 


Spirifer Kentuckensis 
Athyris subtilita. 
Pseudomonotis radialis. 
Pseudomonotis sp.? 
Dentalium Meekianum. 
Chatetes. 

Fenestella. 
Trematopora. 


These beds are almost in contact with the overlying Weber quartzites, 
and their peculiar position with regard to the rest of the range is probably 
solvable by a system of faults, some of which have been clearly observed. 
Their facies is higher than the usual Coal Measure horizons of the Wah- 
satch limestone, and represents the very uppermost limit in their longitude. 
The Waverly horizon was not here observed, but it is clear that the Upper 
Helderberg fossils occur in a horizon not far from the bottom of the Wah- 
satch limestone, and are overlaid by 5,000 feet which contain at intervals 
true Coal Measure forms, although the beds closely overlying the Helder- 
berg, in which we might expect to find both the sub-Carboniferous and 
the Waverly, are here, so far as our observations go, entirely barren of 
fossils. 

In the little fragment of gray siliceous limestone which rests uncon- 
formably upon the granite of the Wachoe Mountains at Castle Peak, were 


PALZOZOIC EXPOSURES. 203 


found Productus sub-horridus and Athyris Roissyi. Southward, in continua- 
tion of the same uplift, at the northern extremity of Antelope Hills, two 
inconsiderable masses of limestone rise above the general field of rhyolite, 
~ and show alternation of limestones and siliceous and argillaceous limy shales, 
characteristic of the upper middle part of the Wahsatch limestone. 

From the Egan Mountains north of our southern limit, with the excep- 
tion of a small body of rhyolite which, in the northern end of the range, 
north of Mahogany Peak, breaks through the limestones, the range is com- 
posed of the Wahsatch body. At Mahogany Peak were obtained — 


Productus multistriatus. 
Productus sub-horridus. 
Athyris subtilita, var. Roissyt. 


From Gosiute Peak were obtained Productus punctatus and a fragment 
of Campophyllum, and still farther down an undeterminable species of 
Diphyphyllum. The facies of the fossils, and the great thickness of the 
limestone exposed—not less than 4,000 feet—refer this great ridge un- 
questionably to the Wahsatch; and although the lower members of the 
series are not reached, the occurrence of Silurian a little farther to the south 
in the range suggests the desirableness of further search for the Waverly 
and Helderberg beds by whoever shall explore south of our limit. 

The Ruby group, which lies between Egan Range and Ruby Valley, 
exposes a considerable thickness of heavy drab, cream-colored, and blue 
limestones, undoubtedly of the same series as Egan Range, although they 
represent, both lithologically and by their fossil remains, higher members 
than are seen on thatrange. Among the collection made were the follow- 
ing Lower Coal Measure forms: 

Productus multistriatus. 
Productus semireticulatus. 
Productus Nevadensis. 
Spirifer pulchra. 

Athyris subtilita. 

Athyris Roissyi. 


From Frémont’s Pass south to Hastings’s Pass the entire Humboldt 


204. SYSTEMATIC GEOLOGY. 


range is made up of conformable rocks dipping to the east, having about 
1,000 feet of quartzite, referred to the Ogden group at the base of the series, 
and skirting the foot-hills on the western side of the range. Above this, 
and forming the whole body of the range and its eastern slope, is a superb 
exposure of Wahsatch limestone, between 6,500 and 7,500 feet in thick- 
ness. The average dip of this whole body is from 16° to 20° eastward, 
increasing to the south to as much as 25°. The eastern slope in the region 
of Ruby Lake is scored by remarkable narrow, deep canons, with abrupt 
walls, nearly perpendicular, reaching 1,400 or 1,800 feet in height. Plate 
XI. illustrates one of these sharp cuts in the Wahsatch limestone. At the 
northern end of the exposure the limestones come directly in contact with 
the granite and gradually rise to a vertical position, tailing out to the north 
as a mere narrow blade of beds on edge. On the high peak back of Cave 
Creek the dip is only 16°; farther south it becomes nearly horizontal, but 
rises rapidly again north of Hastings’s and east of Fort Ruby, where it reaches 
an angle of 16° and 20°, inclined to the northeast. While as a whole the 
ridge is an easterly dipping mass, it will be seen that it describes a slight 
curve, with convexity to the west, and the extreme ends of the curve dip 
slightly toward each other. This is only one of those instances of curved 
strike so frequent in the Basin ridges The Wahsatch group is unmistakably 
conformable with the quartzites below, and the transition between the two 
rocks is made in very short distances, without any noticeable intercalation of 
beds. As they approach each other, the-quartzites become slightly caleare- 
ous, and the limestones somewhat siliceous, yet the line of demarkation can 
be easily observed. The lower limestones, for about 1,500 feet, are of light 
grays and buffs, interrupted by a few dark-blue strata. Above this the bed- 
ding becomes heavier, the limestones darker, and there are more intercala- 
tions of shaly material. On the eastern base there is a great deal of 
unimportant siliceous interstratification, and not a little buff, shaly lime- 
stone. As a whole, from bottom to top, the 6,000 or 7,000 feet are essentially 
a limestone, only varied by small proportions of clay and sand. Midway 
are some beds which are purely dolomitic. One of these saccharoidal 
magnesian stones, taken from about the middle of the series, was analyzed, 
and its result will be found in the tables of analyses of stratified rocks. 


at 


ot 


PALMOZOIC EXPOSURES. 205 


Scattered through the higher members are fragments of recognizable Coal 
Measure fossils; but the lower members have yielded only stems of 
Cyathophylloid corals and a few badly preserved S'pirifers. The only 
identifiable fossil species obtained are in the horizons of the Coal Measure 
forms: 


Chonetes granulifera. 
Productus Nebrascensis. 
Fusilina cylindrica. 


Although faithful search was made at several points through the lower 
members of the series, no fossils were found, owing to the somewhat altered 
condition of the strata. Where the main South Fork of Humboldt River 
flows out from its cafon on the western slope of Humboldt Range, north 
of Frémont’s Pass, the Archean mass projects westward in a bold prom- 
ontory. Around its western base is wrapped a series, about 4,000 feet 
thick, of limestone, overlaid to the north, west, and south by the horizontal 
Pliocene strata. They describe a crescent-curved strike, and dip normally 
outward at angles of about 25°. Near the bottom is a slight exposure of 
conformable quartzite, which is assumed to be the top of the Ogden. The 
first 1,800 feet are of a prevailing light color, with shades of gray and 
buff, but mostly covered with earth and débris and yielding no fossils. 
Above these comes a dense, blue-black limestone, containing the following 
species : 

Productus semireticulatus. 
Productus longispinus. 
Fusilina cylindrica. 
Camarophoria. 


Farther north, in the region of Sacred Pass, the upper members of the 
series yield— 

Syringopora multattenuata. 

Productus costatus. 

Athyris subtilita. 


White Pine Mountains, a group culminating about thirty miles south of 


206 SYSTEMATIC GEOLOGY. 


our southern limit, were visited by several members of the Expedition in 
the prosecution of mining studies. Here is obtained, though not an entire 
section of the Wahsatch limestone, decidedly the most important one in 
western Nevada. The base of the series passes under the Quaternary accu- 
mulation of a mountain valley, and its lower geological boundary is there- 
fore not determined. Nor is the upper limit of the series obtained, but a 
body of 5,000 feet is exposed, which near the base has the most interesting 
lithological sequence of beds, each charged with characteristic fossils illus- 
trating the complete passage from the Devonian through the Waverly and 
sub-Carboniferous into the Coal Measures. On Treasure Hill are actually 
exposed about 1,500 feet of blue limestones, all dipping to the east. The 
upper 800 feet of these offer conclusive evidence of Devonian age. The 
species obtained from these Devonian strata have been determined by Hall 
and Whitfield to range from the Upper Helderberg to the summit of the 
Chemung. Among them are the following: 


Cladopora prolifica. 

Diphyphyllum fasciculum. 
Acervularia pentagona. 
Ptychophyllum infundibulum. 
Naticopsis sp.? 

Orthoceras Kingii. 

Strophodonta Canace. 

Productus subaculeatus. 

Atrypa reticularis. 

Rhynchonella Emmonsi. 

Pentamerus sp.? 

Spirifera argentaria 

Cryptonella Rensellaria. 

Orthis sp.? (resembles O. resupinata). 
Spirifera sp.? (resembles S. striatus). 
Paracyclas peroccidens. 

Bellerophon Neleus. 

Isoneima sp.? 


PALMOZOIC EXPOSURES. 207 


The section from Babylon Hill included— 


Syringopora Maclurit ? 
Smithia Hennahit. 
Favosites sp.? 

Atrypa reticularis. 
Rhynchonella Emmonsi. 
Pentamerus sp.? 
Orthoceras sp.? 
Pterinea sp.? 


The only forms obtained from Mount Argyle belong to corals. Although 
they are mostly fragments, Professor Meek has identified the following: 


Alveolites multiseptatus. 
Cladopora prolifica. 
Smithia Hennahii. 
Dyphyphyllum fasciculum. 


From the Blue Ridge, in the top of the series, we have — 


Spirifera Engelmanni. 
Productus subaculeatus. 
Pleurotomaria sp.? 


Above these limestones is a series of calcareous shales, which so far 
have yielded no fossils. But in the siliceous limestone which directly 
overlies them were found, upon Telegraph Peak, stems of crinoide and 
Spirifer Albapinensis, new species of Hall and Whitfield. This specimen 
here underlies a stratum which clearly belongs to the Genesee slates, al- 
though in the Wahsatch it ranges up into a higher horizon and is associated 
with groups of Waverly fossils from Ogden and Logan cafons, which in 
themselves show certain distinct Devonian forms, yet at the same time 
present a general Waverly facies. Above this siliceous limestone, in per- 
fect conformity, is a series of 125 feet of black shales which form a well 
marked geological horizon at this locality, though they have not been dis- 
tinctly recognized elsewhere in the Great Basin. It is a peculiar outcrop at 


208 SYSTEMATIO GEOLOGY. 


best, which will bring to the surface and preserve easily weathered shales, 
and they may well be supposed to exist in the Wahsatch limestone of the 
neighboring ranges, their narrow outcrops covered with earth or débris. As 
shown at White Pine, they are divided roughly into two distinct bodies. 
The lower group is more argillaceous, and the upper more arenaceous; but 
in general appearance they are strikingly similar, though a sharp division 
is indicated by the association of species. From the lower were obtained — 


Leiorhynchus quadricostatus, Hall. 
Aviculopecten catactus, Meek. 
Iunulicardium fragosum, Meek. 
Nuculites triangulatus, H. & W. 
Goniatites Kingii, H. & W. 
Orthoceras cessator, H. & W. 


From the upper beds we obtained — 


Streptorhynchus sp.? 
Spirifera sp.? (resembles S. disjuncta). 
Productus semireticulatus. 


The occurrence of Leiorhynchus quadricostatus, a form characteristic 
of the Genesee slates, in the lower member of the black shales, led Hall and 
Whitfield to regard the horizon as Devonian, while in the upper series the 
equally marked Spirifera, resembling S. disjuncta, was believed by them to 
mark the horizon of the sub-Carboniferous. The sandstones which directly 
overlie these shales contain only vegetable impressions, leaves and stems of 
Lepidodendron and Cordaites, and casts of crinoidal stems similar to those 
observed in the siliceous limestones below. Next above this the great 
body of blue limestone is abundantly furnished with distinct Coal Measure 


forms : 
Diphyphyllum subcespitosuar. 


Zaphrentis sp.% 
Streptorhynchus crenistria. 
Productus semireticulatus. 
Productus prattenianus. 


PALZOZOIC EXPOSURES. 209 


Productus longispinus. 
Productus sp.? (resembles P. Wortheni). 
Productus Nebrascensis. 
Productus costatus. 
Spirifera camerata. 
Spirifera Rockymontana. 
Spirifera planoconvexa. 
Spiriferina spinosa 
Athyris subtilita. 
Athyris sinuata. 
Eumetria punctulifera. 
Terebratula sp. ? 


The value, therefore, of this White Pine section is in its illustration of 
the complete. passage from Upper Helderberg forms through Genesee into 
sub-Carboniferous and up into the Coal Measures. It is also seen that the 
Upper Helderberg has a range of several hundred feet. The same forms 
that were obtained by Mr. Hague from the Coal Measure limestones of 
White Pine recur in a cream-colored limestone at Railroad Canon. It is a 
mere block of the series, dislocated from any traceable connection with either 
mountain mass, and surrounded on all sides by deep valley Quaternary, or 
fields of basalt which overflow it toward the west. It yielded the follow- 
ing forms: 

Chetetes sp.? 

Streptorhynchus crassus. 

Productus semireticulatus. 

Productus prattenianus. 

Productus costatus. 

Spirifera Rockymontana, 

Spiriferina spinosa. 


South and west of Pifion Pass, in Pinon Range, lies a synelinal, 
of which the lowest members upon the western side are Silurian lime- 
stones. They do not come to the surface on the eastern side; but directly 
overlying the Ute-Pogonip body at Cave Creek is the Ogden quartzite, 

14 k 


210 SYSTEMATIC GEOLOGY. 


as before described, showing an exposure of about 800 feet. This curves 
under the synclinal and rises again, occupying the summit of Pition Pass. 
Held in the curve of the anticlinal are seen the lower 2,000 feet of the Wah- 
satch limestone. There is little intercalation at the region of contact between 
the Ogden and the overlying limestone, the latter beds resting sharply 
upon the laminated quartzites. The lower 1,200 feet of the Wahsatch are 
formed of gray, drab, and buff beds, with only occasional intercalations of 
the ordinary blackish-blue limestone. It is a very exact repetition of the 
same portion of the Wahsatch limestone in the neighboring Humboldt 
Range. From 800 to 1,200 feet up in the series the beds yield abundant 
Upper Helderberg forms. These limestones, never exposing over 2,500 
feet, extend southward along the range as far as the southern limit of our 
map, forming, south of Fossil Pass, a singular monoclinal ridge, with a dip 
to the east. The 2,500 feet is a relic of erosion, all the overlying beds 
having been carried away. Upper Helderberg fossils recur at several 
points, although in one place there would seem to be a mingling of Upper 
and Lower Helderberg, but Hall and Whitfield decide that they might all 
occur in Devonian beds; and this decision is sustained by the presence of 
Lower Helderberg below the Ogden quartzite. Near Hot Spring Creek 
the limestones furnish the following forms : 


Dalmania sp.? (closely resembles D. anchiops from Schoharie 
group, New York). 

Edmondia Pinonensis (associated on thesame block with Chonetes and 
Spirifer). 

Orthis oblata. 

Orthis sp.? (resembles O. quadrans). 

Strophodonta sp. ? 

Spirifer Pinonensis. 

Spirifer sp.? (resembles S. arimosa). 

Atrypa reticularis. 

Rhynchonella sp.? 


Several of these species recur near Fossil Pass, on the summit of the range. 


PALMOZOIC EXPOSURES. 211 


Nearly due east from Chimney Station, on the eastern side of the range, 

were found a few fossils, among them: 

Zaphrentis sp.? (figured by Prof. Meek). 

Favosites sp.? 

Cladopora sp.? 

Spirifera sp.? 
Besides these, there were corals not specifically identifiable, but closely 
related to Upper Helderberg forms. 

Mr. Engelmann, geologist of Colonel Simpson’s Expedition, obtained 
from Swallow Canon, in the same range, though south of our work, a col- 
lection of Devonian fossils, which have been described by Professor Meek. 
They embrace— 

Productus subaculeatus. 

Spirifer Utahensis. 

Spirifer Engelmann. 

Spirifer strigosus. 

Atrypa reticularis. 
All of these have been found by us in the Wahsatch limestone of White 
Pine and the northern Pinon. 

In the southern part of Seetoya Range, rising out of an immense mass 
of rhyolite, stands Nannie’s Peak, a granitic nucleus, which has a heavy 
body of Wahsatch limestone dipping from it in every direction; itis a long, 
oval quaquaversal, with the greatest elongation of granite lying north-and- 
south. The best section is seen on Coal Creek, where the strike is nearly 
east-and-west and the rocks dip to the south about 45°, exposing 2,000 feet 
of limestones, capped by a heavy bed of conglomerate that may possibly 
represent the base of the Weber. This locality is interesting because, 
about a mile from the mouth of the creek, and several hundred feet down 
from the highest exposure of rock, is a bed about fifteen feet in thickness 
of black carbonaceous material, passing in places into an impure anthracite 
coal. The section is as follows, beginning at the top: 


1. Conglomerate, possibly the base of the Weber..--.------------ 
asp blueplimtestonos withishalosy f-/.<)2Se02 aoe os Foe eee oe boos ee 100 


212 SYSTEMATIC GEOLOGY. 


Feet 
3. Bluish-black, finely divided argillaceous shales .......--.-..--- 150 
A Coal seam... 2.cto2 5. leas ste. be ne <6 oe eee er 15 
5, -Bittminous shale: = ists 2e-ce-.. oe eee n 50 
6. Gap (nosexp0sure)s...jcc 222. eee (se oer ee 100 
(. (Blacksshale..: 255222 3c oe Seer eee 10 
8. Argillaceous limestone. = 5.22222 222256 eas See ee er 50 
9. Yellowish calcareous sliale.s.42a2---2 see eee eee 200 
10. Drab siliceous limestone, with shaldce a2 32k se eee eee 200 
11. Blue limestone, with seams of white calcite-....-...-.-.--.--- 50 
12... Rusty quartzite... <2 3.1 ite Se oe eres ater arte ere 50 
3. Compact blue fossiliferous limestone.........-..-.----------- 100 
14. Blue limestone and shales 22 =... 52... ee ee ee eee eee eee 200 


From below the coal were obtained the following Coal Measure fossils : 
Productus semireticulatus. 
Syringopora multatienuata. 
Cyathophylloid (fragments). 


Below the canon of the Humboldt, which opens into the valley of 
Carlin, south of the river the Weber quartzites, which at the mouth of the 
cafion stand nearly vertical, decline to the east, gradually reaching an angle 
of about 40°. Quite conformably under them lies the Wahsatch limestone, 
presenting its edges to the valley, which cuts directly across the strike. In 
rising the hill the limestones quickly pass under overlying volcanic rocks, 
and the exposure is confined to the foot-hills immediately bordering the river. 
Here the limestones are seen to be exceedingly impure, varied with both 
slaty and sandy material, and to show traces of considerable compression 
and alteration. Not far from the top (the actual distance could not be 
determined) are beds of black carbonaceous shales, passing at times into 
the same impure anthracite which has been opened at Coal Creek. Mining 
here has also been actually begun on the carbonaceous streak. There are 
stems of Lepidodendron and obscure vegetable impressions in these shales. 
Farther down, the limestones are again pure, and contain the well known 
association of several species of Productus and the ordinary corals of the 
Coal Measures. 


PALAOZOIC EXPOSURES. Die 


Weser Quarrzire.—Wherever in Oquirrh Range its complicated 
structure exposes the upper limit of Wahsatch limestone, it is seen to pass 
by a series of interealations of limestone and quartzite, characteristic of 
the Tim-pan-o-gos horizon, into Weber quartzite. The latter body is ex- 
posed over fully half of the range, and in the north, at Connor’s Peak, is 
again overlaid by the limestones of the Upper Coal Measures. The exact 
thickness exposed cannot possibly be arrived at, owing to the faulted con- 
dition of the country. It is magnificently shown in the region of Bingham 
Canon, where is exposed certainly as great a thickness as is seen in the 
Wahsatch, and probably a much greater one, approximating to the depth 
of the same series in the Uinta. The Tim-pan-o-gos horizon is finely shown 
at Soldier Canon. Far more than the limestones, the quartzites are liable 
to angular, fragmentary disintegration, and the surface of all the quartzite 
slopes is much more covered and masked by débris than that of the lime- 
stones; hence the structure-lines are much better made out in the under- 
lying and overlying limestones. The greatest quartzite display is in the 
region of Bingham Carion and to the south as far as the mouth of North 
Canon. The structure throughout this region is subject to extremely sud- 
den changes, involving great complications and fractures. The general 
section exposed in Bingham Cation shows a synclinal fold, whose western 
members are short and abrupt, the axis of the fold being depressed toward 
the north. Owing to the irregularity of the structure, it is impossible here 
to arrive at the thickness, but it cannot be less than 6,000 or 7,000 feet. 

In these quartzites Professor Clayton, nearly always successful in his 
search for fossils, obtained the following forms: 


Archaocidaris n. sp. 
Martinia lineata. 
Polypora. 


Crinoid columns. 


Here is an instance in which distinctly Coal Measure forms are found in 
Weber quartzite, and where this is seen overlying Wahsatch limestone. 
The reader will remember, in the Uinta, my mention of the two Coal 
Measure forms which we found in the débris of the quartzite in the heart 


214 SYSTEMATIC GEOLOGY. 


of that range. There was an instance in which the fossils were obtained 
in the quartzite underlying the Upper Coal Measure limestones. The 
Bingham find, which is free from all doubts, lends probability to the 
fragmentary data of the Uinta. These two occurrences of organic forms 
in this wonderful body of quartzite add the final link of proof of its 
age. In the section of Weber Canon the quartzites are seen distinctly 
enclosed between the two great Coal Measure limestone bodies, without 
a shadow of doubt as to the position; and now in two localities Coal 
Measure fossils have been found in the quartzite. After this we conceive 
there can be no dispute as to the age of this member of the Paleozoic. 

In the region of Connor’s Peak the synclinal already mentioned at 
Bingham Canon is again seen, although near the summit of the peak the 
upper beds only of the Weber quartzite are exposed, overlaid by blue 
siliceous limestones and soft, earthy lime beds of the Upper Coal Measures, 
containing poorly preserved specimens of Spirifer and Productus. 

Important masses of Weber quartzite are seen in Stockton Hills, on the 
eastern base of Aqui Mountains, in Cedar Mountains, among the Lakeside 
group, and on Stansbury Island. Otherwise the Salt Lake Basin and the 
hills which skirt it within the limits of our map are composed of no higher 
members than the middle portion of the Wahsatch limestone. 

If the reader will refer to Map IV. of the geological series, he will 
observe that the southern portion of the lower half is composed of ridges 
of Wahsatch limestone and rhyolite, surrounded by fields of Quaternary. 
Northward, however, he will observe that the upper half of the map is char- 
acterized by a very small occurrence of Wahsatch limestone, and by the 
prominence of Weber quartzite and overlying Coal Measures, and that 
only in Tucubits Range is there any considerable occurrence of Wahsatch 
limestone along the northern part of the map. The Gosiute, Peoquop, 
and Little Cedar Mountains, the Toano group, Fountain Head Hills, 
and much of the Tucubits show considerable bodies of Weber quartz- 
ite. Upon the Tucubits it is seen conformably overlying the enormous 
development of Wahsatch limestone. On the other hand, in all other 
ranges—Little Cedar, Peoquop, Ombe, Toano, and Gosiute—the quartzite, 
the lowest rock, is seen to be overlaid by heavy bodies of gray and blue 


PALHOZOIC EXPOSURES. 215 


limestone, varied with certain argillaceous and sandy zones, and carrying 
fossils of the Upper Coal Measure series, to the very base, absolutely in con- 
tact with the quartzite. Such is the faulted and disturbed position, and such 
the irregularity of the quartzite outcrops, that in this section no correct idea 
of their thickness can be obtained. On the Tucubits and Fountain Head 
Hills there cannot be less than 6,000 or 7,000 feet. The other exposures 
display much less. The quartzites so far do not yield any fossil forms in 
this region. The point of interest to us is the persistence of this vast bed 
of quartzite, and the fact of the stratigraphical parallelism with the Weber 
section. 

One of the finest exposures of Weber quartzite in this region is that of 
Pilot Peak, Ombe Range. Directly south of Patterson Pass a body of quartz- 
ite is seen to rest nonconformably upon the granites of the pass, and to oc- 
cupy the entire ridge down to Pilot Peak. This body is composed of beds 
of white quartzite, having rather a complicated structure, evidently sub- 
jected to great lateral compression, and accompanied with frequent local 
displacements In general, there is evidence of a synclinal and an anticlinal 
fold, their axes traced diagonally across the range. Pilot Peak itself is upon 
the anticlinal, the beds striking north 15° to 20° east, with a dip of 15°, 
the greater part of the rock mass inclining to the southeast. Along the east- 
ern face of the mountain is seen a precipitous section of the quartzite edges, 
displaying about 7,000 feet. Lithologically it presents no very great varia- 
tion. It is all rather heavily bedded, with distinctly marked divisional 
planes. Near the southern end of the body it has a prevailing bluish-gray 
or brownish-gray color, while on Pilot Peak it is pure snowy white, passing 
down into a deep bluish tinge, the lower beds being more or less feldspathic 
and interrupted by sheets of conglomerate, whose pebbles are formed of 
quartzite and jasper, evincing considerable compression and cracking. Here 
are interposed also a few thin sheets of silver-gray micaceous schists. 
There is nowhere a finer instance of the method of disintegration of 
quartzite bodies than is shown on the eastern slope, which is covered with 
huge cuboidal blocks of débris, indicating the ease with which it was shat- 
tered by frost. The summit region is characterized by open fissures or 
rents in the quartzite, with walls 200 or 300 feet deep. Subjected to analy- 


216 SYSTEMATIC GEOLOGY. 


sis, the quartzite of this peak gave 94.93 per cent. of silica, .17 of water, with 
the remainder of alumina, lime, and the alkalies. At the southern end of this 
mountain mass the quartzites are conformably overlaid by gray limestones, 
from which, in close proximity to the quartzites, were obtained Productus 
punctatus and Spirifer cameratus; this relation serving to fix the age of the 
quartzite. 

In Fountain Head Hills is a wide display of quartzitic rocks, which 
are continuous westward aéross the saddle connecting that body with 
Tucubits Range, and sweep up to form the crest of the range and its 
eastern slope. The quartzite, as displayed in Fountain Head Hills, is a 
great bed of angular quartzitic conglomerate, a feature which to the west 
of this point is persistent across northern Nevada as far westward as the 
Paleozoic is known to continue. It is a medium-grained, sugary rock, 
made up of angular fragments of flints and cherts of various colors, in which 
black and red invariably predominate. The matrix is a yellowish-brown, 
iron-stained, saccharoidal quartz, having to the touch a peculiar earthy 
feeling. Under the microscope it is seen to contain a considerable propor- 
tion of minute crystals of calcite, the matrix being made up of both erypto- 
crystalline grains and rounded fragments of quartz. 

Near its northern end Tucubits Range is formed of beds of quartzite 
which conformably overlie Wahsatch limestone. Much of the quartzite is 
curiously banded with a cherty material, showing black and green colors. 
The whole of this ridge, and the country south of it overlying Tulasco 
Peak, are much covered with débris and dislocated blocks cf quartzite. Con- 
tinuous outcrops are never found of sufficient extent to permit a measure- 
ment of the thickness. South of Tulasco Peak the brecciated quartzites are 
again seen, full of grains of limpid quartz enclosed in the rough saccharoidal 
matrix, and singularly resembling certain forms of rhyolite. The brec- 
ciated quartzites here again contain an enormous amount of cherty frag- 
ments, brown and black, the matrix being more or less yellow-stained by 
oxyd of iron. The alumina proportion seems to rise in the brecciated region. 

At Middle Pass in Gosiute Range the lowest rock displayed is a small 
mass of granite, which occupies the pass itself. Directly to the north and 


south it is overlaid by Weber quartzite, which towers into hills 1,500 or 


PALAOZOIC EXPOSURES. PA ff 


2,000 feet in height. Both north and south the quartzites are overlaid by 
the limestones of the Upper Coal Measures, carrying characteristic fossils 
nearly down to the contact between the two series, thereby clearly iden- 
tifying the Weber body. The quartzite here is mainly pure white, with 
bands showing bluish and gray sheets, with a few thinly bedded regions of 
almost jet-black jasper. It appears to be made up of two sizes of grains, 
metamorphosed and condensed into a compact rock. The microscope de- 
tects thin flakes of mica, sometimes aggregated into layers, and the quartz 
grains which have not lost their original outlines, although much flattened 
and compressed, show numerous fluid inclusions. Conglomerate beds 
appear in the Quartzite near Orford Peak, characterized by coarse sub- 
rounded pebbles of chert and flint, overlying a heavy mass of yellowish 
quartzite, the whole having a strike of north 28° to 30° east, dipping at an 
angle of 30° to the northwest. Overlying the conglomerate is a thin bed 
of dark, steel-gray quartzite. Upward the series rapidly rises into contact 
with the conformable limestones, which bear fossils of the Upper Carbon- 
iferous. 

River Range, north of Humboldt River, is for the most part made up 
of a long anticlinal of Weber quartzites, flanked on both sides by Pliocene 
valleys, and more or less interrupted and limited by bodies of rhyolites. At 
the extreme southern end, and near the north, occur the overlying lime- 
stones of the Upper Carboniferous. No very deep exposures of the quartz- 
ites were obtained in this region, not over 4,000 feet at the utmost. The 
deepest are seen at Penn Canon, where the structure is that of an anticlinal 
whose eastern member is almost perpendicular, while the main body of the 
range is formed of westerly dipping beds, with angles at the centre of the 
range of 10°, steepening to 25° on the western foot-hills. The lowest ex- 
posed strata show a considerable thickness of argillaceous schists and 
quartzites, which are overlaid by conglomerates, generally including a cer- 
tain proportion of angular cherty fragments, while the most prominent beds 
of all are the peculiar dark, angular conglomerates already mentioned. In 
the upper part of the series is an included bed of limestones underlying an 
upper series of conglomerates, which are apparently always rounded. The 
conformable overlying Upper Coal Measure limestones carry their charac- 


218 SYSTEMATIC GEOLOGY. 


teristic fossils down to the point of contact, as will be seen when treating 
of that limestone. In close connection with the group of rhyolites which 
bounds River Range, are some finely angular conglomerate quartzites, con- 
taining a great number of grains and cryptocrystalline fragments of limpid 
quartz and angular chips of black and green chalcedony. Associated with 
these are peculiar striped felsitic rocks, interbedded with the quartzites, and 
having the appearance of felsitic tufas, contemporaneous with the Weber 
quartzite. 

In Osino Canion, where Humboldt River and the Pacific Railroad cross 
the end of Elko Range, is exposed a good section of steeply dipping quartz- 
ites and conglomerates, the latter of the angular chert-bearing member. 
The general structure is that of an anticlinal fold having a north-and-south 
strike, the beds being upturned at high angles. Here again the quartzites 
contain black carbonaceous seams. 

At Moleen Canon, a mile and a half below the upper mouth, may be 
seen the contact between the Upper Coal Measure limestones and the Weber 
quartzites. There is here an apparent nonconformity, the beds of lime- 
stone having a slighter dip than the quartzites; but this is probably due to 
a fault which is evidenced on the hills to the north and south. The upper- 
most observed beds of the Weber are formed of angular cherty conglom- 
erates, with saccharoidal siliceous cement, which is more or less mixed with 
feldspar fragments, and, as the microscope shows, with carbonate of lime. 
These angular conglomerates do not form the uppermost members of the 
series, and that is an additional argument in favor of an explanation of 
the discrepancy of angle at the contact by a fault, since the lower or angular 
conglomerates are brought into contact with the limestones. A further proof 
that the angular conglomerates are not the uppermost beds is shown at Mo- 
leen Peak, where the lower and northern foot-hills of the group are formed 
of Weber quartzite for 1,000 feet up the foot-hill slopes. Here the quartz: 
ites are of broad, heavy bedding, and of yellow, green, and purple colors, 
with a coarse texture, resembling that of the upper part of the Weber 
group on Mount Agassiz, Uinta Range. The quartzites enclose numerous 
beds of conglomerate of purple and green siliceous pebbles, which are never 


so angular as those of the lower members. The quartzitic conglomerates 
= | 


PALHOZOIC EXPOSURES. 219 


are here conformably overlaid by the gray limestones of the Upper Coal 
Measures, which carry numerous fossils down to within a few feet of the 
contact with the Weber. 

As displayed in the upper portion of Seetoya Range, the Weber 
quartzite, which there conformably overlies about 4,000 feet of Wahsatch 
limestones, is interesting as illustrating the recurrence here of the Tim-pan- 
o-gos horizon, namely, the intercalation of upper limestone beds of the 
Wahsatch with the lower members of the Weber. At this horizon are 
numerous calcareous slates. Although between the upper limits of the 
quartzite, as displayed northwest of Seetoya Peak, and the body of rhyo- 
lites that forms the eastern base of the range, there are a few exposures of 
a limestone which overlies the Weber, no fossils were obtained, and there 
is uncertainty whether this is the Upper Coal Measure or the Wahsatch 
again faulted to the surface. An estimate of the thickness in this region 
would therefore be liable to serious error. 

The southern part of the Seetoya group shows an immense mass of 
Weber quartzites extending as far up as Mount Neva. It is of crystalline 
texture, containing more or less siliceous argillites, with cherty seams. One 
particular bed was noticeable for its wavy structure, accompanied with a 
plentiful inclusion of graphite. 

At Agate Pass, in Cortez Range, occurs a large body of quartzites with 
characteristic included angular chert conglomerates, which are only of 
interest as showing the remarkable persistence and thickness of this peculiar 
development of the Weber. There is not less than 3,000 feet of coarse, 
saccharoidal rock, of which the matrix is made up partly of quartz and partly 
of feldspar grains, with a considerable proportion of microscopical earbon- 
ate of lime. A singular feature of the rocks is the constant occurrence of 
small vugs lined with crystals of quartz and calcite. The siliceous pebbles 
here reach five or six inches in diameter and are partly well worn, rounded, 
littoral pebbles, and partly sharply angular fragments of similar cherts. 

The great mass of Shoshone Peak and the western foot-hills of the 
northern prolongation of Shoshone Range up to the Union Pacific Rail- 
road, are formed of a great body of quartzites, schists, and quartzitie argil- 


lites. Their prevailing strike is a little west of true north, with a dip of 35° 


220 SYSTEMATIC GEOLOGY. 


to the east. They ure frequently finely laminated, and at the lower horizon, 
at the base of the quartzitic series, they pass into blue calcareous bands, 
with a little pure limestone, supposed to represent the Tim-pan-o-gos hori- 
zou. Within the lower limestones, near Argenta, in a limy schist, is a bed 
of carbonaceous shale which in places inclines to anthracite and has been 
actually mined for coal. The Shoshone mass itself shows an expansion 
of quartzites of sixteen miles, at right angles to the trend, and extend- 
ing for twenty miles on the strike-direction, the eastern foot-hills being 
covered with belts of rhyolite from two to five miles broad. These 
quartzites have a southerly and easterly, though chiefly easterly, dip 
The uppermost layers of the quartzite are compact and dark, interbedded 
with thin sheets of fine, fissile, argillaceous slates, which, after a gradual 
calcareous transition, are capped with beds of quite pure limestone. These 
beds yielded no fossils, and the whole series of argillaceous and calcareous 
rocks nowhere exceeds an exposure of 200 feet in thickness. As there is 
some uncertainty about the age of these rocks, and as the only clews are 
given by the bed of impure anthracite near Argenta, and, further, since the 
actual connection between the coal-bearing rocks of the northern foot-hills 
and the immense quartzitic exposure near Shoshone Peak cannot be proved 
to be free from faulting, we content ourselves with referring this to the 
Weber, on a basis of simple probability. In general, the great Shoshone 
body cannot be less than 10,000 feet thick, composed for the most part 
of dark quartzitie schists, with some beds of almost jetty-black chert, a few 
argillaceous seams, and a rather limited amount of conglomerate carrying 
the angular pebbles of chert, the whole dipping eastwardly, or from Reese 
River Valley. 

On the opposite or western side of the valley rises the isolated mass of 
Battle Mountain, which, with the exception of a few masses of limestone 
(one on the summit of Antler Peak, and another bordering the western side 
of the body), is composed of a similar series of quartzitic schists, which, 
although much disturbed and of varying angle, has a pretty general dip 
to the west. These two similar bodies face cach other on the two 
sides of Reese River Valley, standing in the position of a broad anticlinal. 


On the Shoshone side the overlying limestones amount to nothing strati- 


PALHOZOIC EXPOSURES. 221 


graphically, and yield no fossils. In Battle Mountain the upper limestones, 
as exposed at the mouth of Willow Creek, yield Coal Measure forms 
down very close to their contact with the quartzite, and forms which are 
more allied to the Upper Coal Measures than to the Wahsatch limestones. 
For that reason the underlying quartzites, although of prodigious thickness, 
certainly not less than 10,000 feet, allowing then, even, for considerable 
reduplication of fault, are, with some doubt, referred to the Weber. This 
is the most westerly exposure of the series, and also the most western point 
of Paleozoic outcrop. Beyond this meridian, quite to the Sierra Nevada, 
the oldest fossiliferous rocks are Trias, which are seen to rest directly, with- 
out underlying conformable rocks, upon the Archzean. 

Upper Coat Merasures.—In the region of Great Salt Lake, as dis- 
played upon the western half of Map HI, there are no known outcrops of 
the Upper Carboniferous except im the single locality of Connor’s Peak, 
in the northern part of Oquirrh Range, where have been obtained a 
few Upper Coal Measure species in beds of gray limestone overlying 
the enormous thickness of Weber quartzite. Northwest of Salt Lake, 
and north of the map, is a large province chiefly made up of Weber 
quartzite, overlaid by limestones of the Upper Coal Measure series They 
make their appearance at the southern end of the Ombe Mountains, 
south of Pilot Peak, and at the town of Buel. So far as could be ob- 
served, they are quite conformable with the Weber quartzites. Among 
the most important localities, as illustrating the relation of the two 
series, are the hills both to the north and south of Toano Pass. Directly 
north of Fairview Peak the quartzites are seen to be conformably overlaid 
by limestones which dip to the northwest. From a cherty band near the 
top of the ridge the following Brachiopoda have been recognized— 


Productus Rogersi. 
Spirifer pulchra. 
From the limestones adjoining the cherty band were also obtained — 
Productus Nebrascensis. 
Spirifer crassus n. sp. 
Cascinium. 


229 SYSTEMATIC GEOLOGY. 


Northwest of Montello Station, where the limestones directly overlie the 


quartzites — 
Spirifer pulchra and 


Productus Nebrascensis 

were collected, thus proving the limestones to belong to the upper series, 
and not to the Wahsatch. The rocks are largely of calcareous shales, gray 
and yellow, intercalated with beds of solid blue limestone. Higher in the 
series they seem to be more uniformly of the bluish-gray rock. Here 
and there appear a few beds which are exceedingly dark, almost black, 
the color being due, as the microscope shows, to the presence of carbon. 
In the group of hills northwest of Toano the limestones are altogether 
similar, though no fossils were discovered here. The upper limestone mem- 
bers are in general quite heavily bedded, and more or less seamed with white 
calcite. There is an intercalated bed of black siliceous limestone, hard 
enough to seratch glass, but effervescing freely with acids. The micro- 
scope shows it to be made up of fragments of angular and sub-rounded 
quartz, calcite, and opaque carbonaceous particles. Low in the series is 
quite a development of calcareous shales. South of Toano Pass the rocks 
in the region of Owl Valley and along the western half of the range are 
formed of easterly dipping Weber quartzite, conformably overlaid by a 
body of limestone showing not less than 1,500 or 1,600 feet in thick- 
ness. Near the base of the series, intercalated in the limestone, is a 
body of quartzite about 250 feet thick. The overlying limestones con- 
tain indistinct impressions of Spirifer and Productus. South of Middle 
Pass, at Pine Mountain, the quartzites are again overlaid by a westerly 
dipping body of limestone, which yielded Spirifer opimus and Athyris 
subtilita, both forms common to the two bodies of Coal Measure lime- 
stones. 

In Peoquop Range, directly south of Peoquop Pass, is a fine exposure 
of Upper Coal Measure limestones, conformably overlying the Weber. 
On the western side of the range, they have a dip in general to the 
west, though directly to the south of the pass they describe a broad curve 
and reach a northeasterly dip. Immediately above the quartzites the lower 
beds of limestone yield — 


PALMOZOIC EXPOSURES. 223 


Producius semireticulatus. 
Spirifer cameratus. 
Discina sp.? 


Orford Peak, the high summit southeast of this pass, which reaches an 
elevation of 7,556 feet, carries upon its crest a body of limestone isolated 
from the main mass, and probably thrown up by dislocation and not alto- 
gether eroded off. It is only 150 to 200 feet in thickness, and directly 
and conformably overlies the Weber quartzite. It contains — 


Athyris carbonaria. 
Productus semireticulatus. 
Productus punctatus. 
Productus Nebrascensis. 
Productus longispinus. 
Spirifer cameratus. 
Athyris subtilita. 

Athyris Roissy. 


Associated with these were corals of the genus Campophyllum. Through- 
out the limestones of the northern end of the Peoquop are frequent inter- 
stratifications of cherty material, often carrying nodular concretions of flint 
and banded strata of exceedingly fine-grained cherts, with narrow bands 
of chalcedony. When treated with acids, the most siliceous specimens give 
a slight reaction for carbonate of lime. 

North of Independence Spring the limestones which extend south 
from the high mass of Euclid Peak conformably overlie the Weber 
quartzites and carry in their very lowest beds Productus semireticulatus, and 
bryozoa belonging to the genus Trematopora. 

South of Cedar Pass the Little Cedar Mountains are for the most part 
made up of heavy exposures of Weber quartzite, overlaid on the east by 
limestones of the Upper Coal Measure series, dipping to the east at angles 
varying from 10° to 22°, and passing under the shallow Quaternary deposit 
of the valley to form, with the westerly dipping limestones of the Peoquop, 
a synclinal. In this limestone were obtained several bryozoa, together with 
Productus sub-horridus. Insimilar but westerly dipping limestones on the 


224 SYSTEMATIC GEOLOGY. 


western side of the range, still conformably overlying the quartzite, were 


found — 
Productus prattenianus. 


Athyris subtilita. 
Syringopora multattenuata. 
Chatetes sp.? 


On the summit of the ridge, a little north of Albion Peak, a fragment 
of the lowest beds of the limestone has been spared from the general erosion 
of the region. The limestone, when subjected to analysis, besides a small 
proportion of white quartz sand, showed the theoretical composition of dolo- 
mite. 

West of this point the region throwing most light on the Upper Coal 
Measure series is the neighborhood of Moleen Canon. The southern end 
of River Range, for a distance of twelve or thirteen miles northwest from 
Moleen Canon, shows the Upper Coal Measure limestones conformably 
overlying the Weber quartzite. They are composed here of a highly 
varied series of limestones, often earthy and marly, containing many zones 
of gray and yellow shales and some hard, heavy beds of black carbona- 
ceous limestone emitting a foetid odor when struck with the hammer. 
About four miles north of Moleen Canon were found, in close proximity to 
the contact-plane between the limestones and underlying Weber quartz- 
ites, Productus sub-horridus and Athyris subtilita. The Athyris was also ob- 
tained from the very uppermost members of the limestone, where they pass 
under the Quaternary of Humboldt Valley, showing a vertical range of 
about 1,000 feet. South of the river, at Moleen Peak, is a display of lime- 
stones overlying the Weber quartzite. The whole series has an inclination 
to the southeast of 5° to 8°. These two masses, the Moleen mass and the 
southern part of River Range, directly across the valley, have a similar 
dip, and between them there seems to be insufficient room for the other 
member of a fold. They are therefore regarded as parallel monoclinal 
uplifts, the result of dislocation. The conformable contact-plane between 
the limestones and the Weber quartzite is very distinct, and there are only 
the slightest intercalations. On the other hand, the upper members of the 
quartzite, especially the matrix of the conglomerate, contain a great deal of 


PALAOZOIC EXPOSURES. 995 


ra 


carbonate of lime, and the lower members of the lime series are highly 
siliceous and more or less argillaceous. From 150 to 200 feet from the 
bottom were obtained — 


Productus sub-horridus. 
Productus symmetricus. 


About 300 feet higher in horizon — 


Productus sub-horridus. 
Athyris subtilita. 
Spirifer cameratus. 
Zaphrentis Stansburyi. 


And from a third horizon a little below the summit of the peak, say 1,200 
feet above the quartzite, were obtained — 


Productus sub-horridus. 
Productus semireticulatus. 
Productus prattenianus. 
Productus symmetricus. 
Streptorhynchus crassus. 
Orthis carbonaria. 
Eumetria punctilifera. 


The extreme western point to which the Paleozoic series extends in 
our belt, as already mentioned under the head of ‘Weber Quartzite,” is 
the group of Battle Mountain. There, with apparent conformity, upon the 
summit of the great quartzite body on Antler Peak, is a mass of isolated 
limestones; but a little to the west and south the same strata recur inclined 
to the westward at dips of about 20°, well displayed upon Willow Creek, 
where they form a precipitous wall of 1,200 to 1,500 feet of dark-gray 
limestones, in places somewhat shaly. In the lowest exposures in Willow 
Canon were found the following Carboniferous forms : 


Productus semireticulatus, 
Productus prattenianus. 
Eumetria punctilifera. 


Athyris incrassata. 
15 kK 


226 SYSTEMATIC GEOLOGY. 


About 100 fect below the summit of the peak, and separated from 
the last locality by about 1,000 feet of limestone, the following fossils of 
entirely distinct generic forms were collected : 


Fusilina cylindrica. 
Spirifer pulchra. 
Campophyllum. 


The Upper Coal Measures, as a whole, over the Great Basin part of 
the Fortieth Parallel area, are a single body of limestones varying as to 
chemical purity and mode of stratification, reaching 1,600 or 1,800 feet in 
thickness. It rests conformably on the Weber quartzite, and in this region 
is the uppermost member of the Palzozoic series, the Permian never appear- 
ing west of the Wahsatch. 


Sh CEO Nhe: 
RECAPITULATION OF THE PALHOZOIC SERIES. 


Analytical Geological Map II. accompanying this chapter shows all the 
Paleozoic exposures within the Fortieth Parallel area. At a glance it will 
be seen that the Rocky Mountain region has only a very slight development 
of Paleozoic rocks, and they appear simply as the bordering foot-hills of the 
Archzan mountain masses. Between the eastern boundary of the work, 
in the neighborhood of longitude 104° and Wahsatch Range, the greater 
part of the surface of the country is so deeply covered with Mesozoic and 
Tertiary rocks that little is seen of the underlying Paleozoics. It is 
only in the great Uinta uplift that the low-lying rocks make their ap- 
pearance. It is quite clear, however, that, with the exception of the lofty 
insular Archean bodies at the east, the Palzeozoic forms a continuous sheet 
over the whole area beneath the later rocks. On the map accompanying 
this chapter the Archean and granite exposures are shown for the purpose 
of illustrating their relation to the Paleozoic series. In Wahsatch Range 
and in the series of desert ranges which lie to the west as far as longi- 
tude 117° 30’ there is no considerable mountain body without its 
exposure of Palzeozoic strata. In nearly all, the Archean rocks also 
come to the surface, and almost every mountain block is therefore an illus- 
tration of the relation of nonconformity subsisting between the two great 
groups. Within the Paleozoic there are no considerable passages of met- 
amorphism, no tendency to the formation of gneissoid rocks or erystal- 
line schists, such as are described by some authors in the Appalachian sys- 
tem. As already mentioned, the Paleozoic series are strictly conform- 
able, from the lowest Cambrian beds up to the top of the Upper Coal 
Measure limestones. Between this vast series and the group of shales 
and argillaceous limestones of Permo-Carboniferous age which close the 
Paleozoic age, there is little, if any, discrepancy of angle at the locali- 


227 


228 SYSTEMATIC GEOLOGY. 


ties observed by us, but there is a slight appearance of nonconformity by 
erosion. In the Wahsatch region the limestone surface seems to have 
been acted upon either by marine currents or by shore waves, result- 
ing in the production of gentle hollows, over which the fine muddy and 
shaly sediments of the Permo-Carboniferous were deposited with a 
slight nonconformity. Our observations are too limited to lay much 
stress upon this very trifling discordance. Below that horizon there is, 
however, no doubt of a strict parallelism over the whole area surveyed. 

The most remarkable feature of the section opened up by our labors is 
the very great thickness of the Paleozoic series from longitude 117° east- 
ward to and including Wahsatch and Uinta ranges, and the rapid thinning 
of the series from that longitude eastward to the Rocky Mountain zone. 
The entire series is not exposed in the most western longitudes. The 
deepest members of the Cambrian are not uncovered there, but the recognized 
members from the bottom of the Primordial limestone to the top of the 
Upper Coal Measures show a thickness even greater than in the Wahsatch 
section. Providing the Cambrian holds at the extreme west the same great 
volume that is displayed in Cottonwood Canon of the Wahsatch, the 
western Nevada section could hardly be less than 40,000 feet conformable. 
In the Wahsatch it is 32,000 feet. The Uinta only shows an imperfect ex- 
posure, nowhere reaching the bottom of the Weber quartzite, and the beds 
of the Rocky Mountain region with us have a maximum of only 1,200 feet. 
The great accumulations of sediment, therefore, lie between the east end of 
the Uinta and the western Paleozoic limit in middle Nevada. Between the 
Wahsatch section and that at the extreme west there are but slight differ- 
ences either in the character of the individual members of the Paleozoic or 
in the total thickness. The area of greatest sedimentation seems to have 
been from longitude 108° 30’ to 117° 30’. 

Referring to Analytical Geological Map I. accompanying the Archzean 
chapter, and observing the ideal section at the bottom of the map, the 
reader will perceive that the bed on which the Paleozoic series have been 
imposed was by no means a plain; on the contrary, it was a vast mountain 
system which had suffered submergence, and over which the Paleozoic 
sediment settled. One feature of importance is the fact that there is little 


RECAPITULATION OF PALZOZOIC. 229 


or no tendency on the part of the sediments of a given horizon to follow the 
hill-slopes, but in all cases where observed they abut directly against them 
as if deposited in absolute horizontality. Owing to the very great height of 
these Archean ranges, reaching in one instance an abrupt cliff slope of 
30,000 feet, the earlier sediments, those of the Cambrian and Silurian, 
must have been deposited chiefly in what were the valleys of the sub- 
merged Archzan mountain system. The base of the Cambrian is never 
seen. To the full section, as observed, there is therefore an unknown plus 
quantity to be added. 

All the Paleontological lines are drawn in conformity with the New 
York system, except that under the term Cambrian I include all the rocks 
from the lowermost Paleozoic exposures up to and including the whole of 
the Primordial. This is the line as drawn by Dana, the only difference 
between his system and mine being that, instead of making the Cambrian a 
part of the Silurian, I follow approximately the English nomenclature, and 
confine the Silurian to the region above the junction of the Quebec and the 
Primordial. 

Naturally the most imperfectly exposed of all the members of the series 
is the Cambrian group. Thus far, among the reported occurrences of the 
rocks of this horizon in the Cordilleras, the locality at the mouth of Big 
Cottonwood Carfion must remain as the finest example and the stratigraphical 
type. The lowest member—the Cottonwood slates, a group about 800 feet 
thick, which here rest upon highly metamorphic Archean schists—has thus 
far yielded no organic forms. Though searched by us with considerable 
care, it presented no indications of life. The rocks are dark blue, dark pur- 
ple, dark olive green, and blackish argillites, all highly siliceous, and as a 
group sharply defined from the light colored quartzitic schists which conform- - 
ably overlie them. This second group, by far the greatest of the whole Cam- 
brian series, is a continuous zone of schists which have a prevailing quartz- 
itic character though varied with a considerable amount of argillaceous mat- 
ter. It would seem to be the product of a fine-grained arkose formation, 
simply compressed into dense schists. From 8,000 to 9,000 feet thick, it 
has a general uniformity of lithological condition from bottom to top, except 
that in the region of Twin Peaks are some phlogopite schists and siliceous 


230 SYSTEMATIC GEOLOGY. 


zones, carrying considerable muscovite. The phlogopite members recur in 
the Egan Cafion region The prevailing colors of this member are gray, 
greenish gray, drab, and pale brown; never dark colors. Conformably over- 
lying it are 2,500 to 3,000 feet of cream-color and salmon-color and white 
quartzites, and quartzo-felsites. Occasional sheets of conglomerate are seen 
in the quartzites not far below the summit of the Cambrian. These as dis- 
played in Ogden Cafion are of extreme interest. All the pebbles are much 
flattened, and not unfrequently they are welded together, squeezed into one 
another, having evidently become plastic when under great pressure. There 
is not a crack or divisional plane in these welded pebbles. The summit 
member is a thin series of green siliceous argillites, which are usually not 
more than 75 or 80 feet thick, and which, in different localities, carry in the 
lower part of the narrow group, fossils of Primordial types, and in the 
upper strata basal Quebec forms. In the region of the Wahsatch arid 
Oquirrh, this little group of argillaceous and sometimes calcareous shales 
holds the division-planes between Silurian and Cambrian. No organic forms 
have been found in the enormous quartzite series. In middle Nevada, 
where again the Cambrian series is displayed, a decided change is found 
to have occurred. The little shale zone has disappeared, and its place is 
taken by a body of dark, steel-gray and ashen-gray siliceous limestone, in- 
tercalated with repeated series of calcareous shales, the entire body of lime- 
stone being about 4,000 feet thick. The lower 2,000 contain abundant 
Primordial fossils, and the upper 2,000 Quebec and later Silurian forms to 
the top of the limestone. This limestone, called from its typical locality, 
Pogonip, is persistent over a considerable region of western Nevada, and 
its lower half always carries Primordial fauna. Only the top of the Cam- 
brian quartzite series is exposed in western Nevada. The true Potsdam 
sandstone, characteristic of the eastern region, and recurring with remark- 
able persistence through the Black Hills and parts of the eastern Rocky 
Mountain system, does not, as such, appear in the middle or western For- 
tieth Parallel area. Conformably underlying the beds of the Carboniferous 
limestone series of the Rocky Mountains is the same fine, gritty, red sand- 
stone which a little north of our map and in the Black Hills carries the 
Potsdam fossils. It is unmistakably the same stratum extending south- 


RECAPITULATION OF PALAOZOIC. 231 


ward into the region of our work, but with us is quite devoid of fossils. 
From the Utah and Nevada Cambrian were obtained the following: 


Lingulepis Mera n. sp. 

Lingulepis ? minuta un. sp. 

Obolella discoidea n. sp. 

Obolella sp.? 

Kutorgina minutissima n. sp. 

Paradoxides? Nevadensis, Meek. 
Conocephalites (Ptychoparia) Kingi, Meek. 
Conocephalites (Pterocephalus) laticeps n. sp. 
Crepicephalus (Loganellus) anytus n. sp. 
Crepicephalus (Loganellus) Haguei n. sp. 
Crepicephalus (Loganellus) granulosus n. sp. 
Crepicephalus (Loganellus) maculosus un. sp. 
Crepicephalus (Loganellus) nitidus n. sp. 
Crepicephalus (Loganellus) simulator n. sp. 
Crepicephalus (Loganellus) unisulcatus n. sp. 
Crepicephalus (Bathyurus ?) angulatus n. sp. 
Chariocephalus tumifrons n. sp. 

Ptychaspis pustulosus n. sp. 

Dikellocephalus bilobatus n. sp. 
Dikellocephalus flabellifer n sp. 
Dikellocephalus multicinctus n. sp. 

Agnostus communis n. sp. 

Agnostus Neon n. sp. 

Agnostus prolongus n. sp. 

Agnostus tumidosus n. sp. 


In the Wahsatch region, overlying the narrow argillite zone, is a body 
of limestone varying from 1,000 to 2,000 feet thick, carrying Quebec 
fossils nearly to its summit. This Ute limestone in passing westward evi- 
dently merges into the greater Pogonip body, lime sediments having gone 
farther down into the Cambrian so as to include 2,000 feet of Primordial, which 
in the Wahsatch is occupied by the salmon-colored and white quartzites. 


232 SYSTEMATIC GEOLOGY. 


The Silurian Ute limestone at its characteristic locality, Ute Peak, is 
a body about 2,000 feet thick, of gray siliceous limestones and calcareous 
shales, carrying Quebec fossils to within 60 or 75 feet of its base and within 
150 feet of the summit At Ute Peak it is never metamorphosed to any 
considerable degree, and rarely shows even the most rudimentary form of 
crystallization. It is essentially an unaltered bed of variable lime and 
sandy sediment, in which the lime so far prevails as to give to the whole a 
general caleareous character. This group is persistent through the entire 
length of the Wahsatch, and is exposed at a great number of points. In 
the region of Cottonwood, where the strata are thrown into an extraordi- 
nary semicircular curve around a nucleus of granite, all the members of 
the Paleozoic are compressed to a very great degree. The Ute limestone 
is here only 1,000 feet thick and is essentially a bed of much shattered 
white marble, containing tremolite and fine quartzitic intercalations. In 
the eighty miles between Ute Peak and the Cottonwood region it is true 
that there is abundant room for great variation in the actual original volume 
of sediment. But it is also true that when subjected to extraordinary com- 
pression, and in passing into the crystalline form, there is a very great 
shrinkage in all limestones, and it is not at all improbable that the difference 
of thickness in the two localities named may be due purely to the effects 
of compression. A similar instance is observed in the limestone of the 
Laramie Hills. On the west flank, where it lies nearly horizontal and has 
never been much disturbed, the series is about 1,200 feet thick, while di- 
rectly across the range, where the limestones are highly crystalline and 
thrown into vertical position, the maximum thickness is inside of 800 feet. 
It is therefore probable that over the area of our map there was no very 
great original variation in the thickness of the Ute limestone. 

In the Wahsatch region no fossils were obtained from the actual 
summit of the group, but in the Wind River region, not far removed to 
the north and east, Comstock, while accompanying the Jones Expedition, 
observed a limestone comprising 200 feet of beds, carrying Quebec fossils, 
capped by 150 feet with forms characteristic of the Niagara. In the south- 
ern Wahsatch the group is too uniformly crystalline to yield fossils. In 
middle Nevada, however, in the region of White Pine, Eureka, Pinon, 


RECAPITULATION OF PALAOZOIC. 230 


and Roberts Peak ranges, the great Pogonip limestone, whose lower half, 
as already described, is charged with Primordial fossils, contains in its upper 
2,000 feet several Silurian horizons. The Quebec probably there occupies 
1,500 feet. From Nevada and Ute Peak in the Wahsatch were obtained 
the following Quebec species: 


Lingulepis Ella n. sp. 

Lingulepis or Lingula sp.? 

Obolella sp.? 

Kutorgina sp. undet. 

Orthis Pogonipensis n. sp. 

Leptena melita n. sp. 

Strophomena Nemia n. sp. 

Porambonites obscurus n. sp. 

Ethynchonella sp.’ (fragments only). 
Ophileta complanata, var. nana, Meek. 
Euomphalus (Raphistoma) rotuliformis, Meek. 
Euomphalus (Raphistoma) trochiscus, Meek. 
Raphistoma acuta n. sp. 

Maclurea minima n. sp. 

Cyrtolites sinuatus n. sp. 

Fusispira compacta n. sp. 

Conocephalites subcoronatus un. sp. 
Crepicephalus (Loganellus) quadrans n. sp. 
Dikellocephalus gothicus n. sp. 
Dikellocephalus quadriceps n. sp. 
Dikellocephalus Wahsatchensis n. sp. 
Bathyurus Pogonipensis n. sp. 
Ceraurus ? sp.? 

Ogygia paraboloidalis n. sp. 

Ogygia producta n. sp. 


At Roberts Peak, about 300 feet from the top of the Pogonip series, 
were obtained the following Niagara forms : 


234 SYSTEMATIC GEOLOGY. 


Cladopora, sp. (resembles C. seriata, Hall). 
Orthis (resembling O. hybrida, Dal., but larger). 
Atrypa reticularis, L. 

Atrypa (resembles A. nodostriata, Hall). 
Tilenus sp. undet. 


The very top of the Pogonip, almost in contact with the basal strata 
of the Ogden quartzite at Roberts Peak and White’s Ranch, has yielded the 
following fossils of the Lower Helderberg horizon : 


Favosites Helderbergia, Hall. 

Diphyphyllum n. sp.? 

Campophyllum (impressions only). 

Crinoidal columns. 

Small branching Bryozoa, too indistinct for 
generic determination. 

Crania sp. undet. 

Orthis multistriata, Hall. 

Orthis n. sp. (resembling young 0. oblata, Hall). 

Strophodonta punctulifera,? Con. (fragments only). 

= Spirifera Vanuxemi, Hall. 

Trematospira ? 

Collospira n. sp. (allied to C. imbricata, Hall). 

Atrypa reticularis, L. 

Rhynchonella, sp. undet. 

Pentamerus galeatus, Dal. (fragments only). 

Cryptonella sp.? (fragments only). 


The next overlying member of the series, the Ogden quartzite, is a 
remarkably persistent and singularly pure sheet of siliceous sediment, which 
has been in general compacted into a quartzite, and which is spread with 
remarkable evenness over the whole Palzeozoic area west of and including the 
Wahsatch. At its typical locality in Ogden Canon, Wahsatch Range, it is 
1,200 or 1,400 feet in thickness; at Cottonwood Canon it is compressed to 
1,000 feet, and where seen in middle Nevada varies from 8V0 to 900 feet. 


RECAPITULATION OF PALAOZOIC. 235 


When examined under the microscope the individual grains of sediment can 
always be detected, and among the siliceous granules are crystals of carbonate 
of lime, a little uniformly distributed carbon, and particles of feldspar. In 
Ogden Canon it is bounded at the top and bottom by thin developments of 
greenish-gray argillites, and about the middle of the quartzite is a thin 
bed of white, slightly siliceous marble. No fossils have ever been found 
by us in this member. It is referred to the Devonian, because directly 
underlying it in the top of the Pogonip limestone are Lower Helderberg 
fossils having marked affinities also with the Upper Helderberg, and at the 
base of the Wahsatch limestone, directly in contact with the upper beds of 
the Ogden, occur plentiful Upper Helderberg forms. It therefore occupies 
the interval between the two Helderberg groups, covering the rocks of the 
Oriskany, Cauda-Galli, and Schoharie epochs. It is hardly possible, from 
the physical condition of the bed wherever seen, that any considerable organic 
forms can ever be found, and it is doubtful whether the precise upper limit 
of the Upper Silurian will ever be definitely arrived at in the Great Basin. 

The next member of the series, the great Wahsatch limestone, first 
appears in the Fortieth Parallel area in the Wahsatch. It is never seen by 
us east of that range. It is a single body of limestone about 7,000 feet in 
thickness, and holds its enormous volume with remarkable evenness wher- 
ever observed over Utah and Nevada. The passage between the Ogden 
quartzite and the Wahsatch limestone is very abrupt, without any con- 
siderable intercalations of quartzite and lime. The prevailing type of 
limestones throughout the whole series is dark and heavily bedded strata. 
Near the base, in western Nevada, are about 1,000 feet of gray and drab, 
slightly marly strata, and always about 1,000 feet from the top there is an 
intermixture of silica, amounting in some cases to distinct beds of sandstone 
or quartzite 100 feet. thick. In the region of this siliceous zone, which is 
never more than 1,200 feet from the top of the series, are also frequent 
earthy impurities, argillaceous and sandy. In the little quartzite intercala- 
tion alluded to is a quite persistent sheet of conglomerate, the pebbles being 
made of dark jaspers. At the top of the series its passage into the great 
Wahsatch quartzite is extremely variable. In Weber Canon the uppermost 


limestones are brick-red, and there are one or two unimportant intercala- 


236 SYSTEMATIC GEOLOGY. 


tions of red sandstone with the lime beds, but the whole transition is made 
within 100 fect, and above that horizon stretches the enormous thickness of 
the Weber quartzite. On the other hand, in the Cottonwood region, more 
especially in the valley of Provo, on the heights of 'Tim-pan-o-gos Moun- 
tain, there is a full 1,000 feet of frequently repeated alternations of red- 
dish-blue limestone and quartzites. The transition, as observed in middle 
Nevada, is usually abrupt like that of the Ogden region, but north of the 
Humboldt are seen the Tim-pan-o-gos intercalations. The lower 1,400 feet 
of this group are distinctly Devonian, yielding fossils of the Upper Helder- 
berg, Chemung, and Genesee. From the Upper Helderberg were ob- 
tained — 

Alveolites multiseptatus, Meek. 

Cladopora prolifica, H. & W. 

Acervularia pentagona, Goldf., Meek. 

Smithia Hennahii Lourd., Meek. 

Diphyphyllum fasciculum, Meek. 

Ptychophyllum infundibulum, Meek. 

Naticopsis sp. undet. 

Orthoceras Kingii, Meek. 


From the upper members of the Devonian, ranging from the Upper 
Helderberg to the Chemung inclusive, were obtained — 


Favosites polymorpha, Goldf., Meek. 
Syringopora Macluri? Bill. 

Smithia Hennahii, Lourd., Meek. 
Cyathophyllum Palmeri, Meek. 
Strophodonta Canace, H. & W. 

Productus subaculeatus, Murch. 

Spirifera Albapinensis n. sp. 

Spirifera argentaria, Meek (very closely allied to S. zigzag, Hall). 
Spirifera Engelmanni, Meek. 

Atrypa reticularis, L. 

Rhynchonella Emmonsi n. sp. 

Pentamerus sp.? 

Cryptonella sp.? = Renselleria sp.? Meek. 


RECAPITULATION OF PALZOZOIC. 23% 


Paracyclas peroccidens n. sp. 
Pterinea sp.? 

Pleurotomaria sp. undet. 
Isoneima, sp.? 

Bellerophon Neleus n. sp. 
Orthoceras sp.? 


In a single instance, at White Pine, the Chemung is overlaid by black 
shales, the probable equivalent of the Genesee group, from which we col- 
lected the following: 


Leiorhynchus quadricostatus, Hall = Rhynch. (Leiorhynchus) papyra- 
ceous, Meek. 

Aviculopecten catactus, Meek. 

Nuculites triangulatus n. sp. 

Linulicardia fragosa = Posidonomya fragosa, Meek. 


The Chemung and Genesee beds are immediately followed, at the 
height of about 1,400 feet from the base of the Wahsatch, by a consider- 
able thickness, probably 300 or 400 feet, of dark, heavy limestones, car- 
rying fossils which have a close resemblance to the Waverly group, but 
which have perhaps a closer affinity with the Devonian. The list consists 
of the following species: 


Michelina sp.? 

Streptorhynchus equivalvis, Hall. 
Streptorhynchus inflatus, HW. & W. 
Strophomena rhomboidalis, Whal. 
Chonetes Loganensis n. sp. 
Productus sp.? (fragments only). 
Spirifera centronata, Winch. 
Spirifera Albapinensis n. sp. 
Athyris Claytoni n. sp. 

Athyris planosulcata? Phillips. 
Rhynchonella pustulosa? White. 
Terebratula Utah n. sp. 
Euomphalus (Straparollus) Utahensis n. sp. 


238 SYSTEMATIC GEOLOGY. 


Euomphalus latus var. lavus, White. 
Euomphalus (Straparollus) Ophirensis n. sp. 
Proetus peroccidens n. sp. 

Proetus Loganensis u. sp. 


Directly above the Waverly, and altogether below a horizon 2,200 
feet up in the series, are dark beds containing sub-Carboniferous forms, 
such as — 


Zaphrentis excentrica, Meek. 

Fenestella sp.? 

Polypora sp.? 

Glauconome sp.? 

Orthis resupinata, Mart.? 

Productus levicostatus, White? 

Productus semireticulatus, Mart. 

Productus elegans, N. & P.? 

Productus Flemingi var. Burlingtonensis, Hall. 
Spirifera striata, Mart. 

Spirifera setigera, Hall. 

Spirifera Keokuk, Hall. 

Spirifera sp.? (resembles S. imbrex, Hall). 
Athyris subquadrata, Hall. 


Sub-Carboniferous fossils are obtained in Oquirrh, Wahsatch, and 
White Pine ranges. 

From this horizon the upper 4,500 feet of Wahsatch limestone are char- 
acterized by abundant Coal Measure fossils. In middle Nevada, at several 
localities, principally at the Coal Mine Canon of River Range, in the hills 
south of Carlin Valley, and in the Pancake Mountains, from 500 to 800 
feet down in the Wahsatch limestone, were observed one or two zones of 
carbonaceous material, almost anthracitic. They have been quite exten- 
sively prospected for coal, and the indications of a considerable coal flora 
are obtained. Stems of Lepidodendron and fragments of broad fronds have 
been collected. Up to this horizon from the bottom of the Cambrian, 
excepting the conglomerate beds, there are no indications whatever of shal- 


RECAPITULATION OF PALZOZOIC. 239 


low water, or of those frequent oscillations of level which mark the corre- 
ponding horizons in the Appalachian Palzozoic.* 

The following Coal Measure forms were obtained from the Wahsatch 
limestone : 


Syringopora multattenuata, McChes. -.--...--.-----.-------------- 3? 
dnihostrotion Wreumeyt, Meek: 5252520552 2.6 5522225028 tee. one eo 32 
Bophopnyuum proujenum, MeCChes.: 2522... 2.85 -.-eseesss5c-5 =. 1 
LGN WAAR ISULLDSUC Ti, EEN RES SRE oe SO ead cd cod es toeaee ace 4 
JAF NORAD DON CUGE DT GE, NING) <t PEES Ee  S SER BE EC o Rene Ooo 1 
Zaphrentis sp.? (resembles Z. centralis, Ed. & Haime) -------------- 3 
Cyathophyllum (Campophyllum) Nevadensis, Meek.....-------------- 1 
ING aes eR see 26 C2 Seas eee CC ona oer Sopa sop eaeeoe 1 
SURCpLonn yp chs ouustus.| alee peepee in fo eal ieiele aia 1 
SUTEDLOTHUMChUS: Chenisinius, lyst tae ss eet ol iia nei = = = 2 
SURCP LON RACHUS ChOSSUS +) WLCCKe 3 oh en Sie cea oe sga t= Syai= ets) afaj 2-20 = = = 2 1 
HUG a GLU IhGD, OM Gils = ae 56 cae! Beene ar Seono Se. EOE aeeeee 4 
eV GRUCTESECONE AU OT Dicer ae cto esa aede beset aie Aer als= apa G"-  Sta 2 1 
IE OGUCLUSE NEULOSCENSIS Mee Kae = 2 ae Bans Se ibes jaysr ore a afene sin e's odie 2 
JERURG TES FUE IGG) Soe ee ere eee 1? 
LONUCHUS: DUNCLOLUS, Marie: § asta > 2a eee aea cia ses oe sicSa class <<less 2 
PLOUUCLUS ON HEHIONUS mNOLWe jor a= Sars 2 aia ee eee 2 aie 4 
roduc SyMmmelmicion MGChESs+. 4-4 5-2-2422 = os2 Fae = 4? 
PPV OUUCTUSE SEMIN EELCILGLUS WL ATL: = 2 ojo 2 om 2 Gre, cle alae a ins clei = ae 6 
Spirifera Rockymontana, Marc. = S. opimus, H.....-..--.---------- 13 


*The figure placed to the right in the Carboniferous lists indicates the num- 
ber of localities at which the species is found, where the position of the bed has been 
positively recognized. The interrogation-point following a number implies that the 
identification in one or more of these localities is questioned. 

It will be noticed that the species peculiar to the particular beds (that is, found 
in only one of them) occur in but few localities, generally only in one, and when found 
in two or more the localities have been contiguous, indicating that the species have 
not a wide geographical range within the territory collected from. On the other hand, 
the species common to both beds occur in several localities, showing a more extended 
range or a more general distribution within the territories. This would reduce the 
stratigraphical value of the species peculiar to each bed in proportion to the number 
of localities from which they have been obtained. 


240 SYSTEMATIC GEOLOGY. 


Spiriferavcameratas *Mort.6 2...) 22 05 2 
Martiniatimeata; Mart... 02-2. DSSS oS ee nn ara eee 4 
Spirterina Mmentuckensis: Shwm.. 22 otae ~ ae eee tee il 
Athyris subtilita, Wall. 2% 122 2.6 ere ee eee 5 
Bhynchonella Osagensis : 22 c2k.< einer eee eee uf 
Terebraiula bouidens, Mort. 2523-22 -5+ eee eee eee ee eee 2 
Cardiomorpha Missouriensis, Swallow .....--.--.----=-----------. 1 
Naticopsis sp: ¥- 2.2 22 so is ee ae te ere eee ee i 
Gontatiles King 22 52. oe ee eee 1 
Oyrtocenas'?: COSSQLOT SE? == 205 AN Be eee eee ee eee 1 


Above the Wahsatch limestone is the equally great Weber quartzite, 
a body of indurated sandstones and quartzites, carrying occasional sheets 
of conglomerate, and interposed between the two bodies of Coal Measure 
limestone. In the Wahsatch it attains a thickness of about 6,000 feet, in 
the Oquirrh 8,000, and in middle Nevada probably considerably greater 
thickness. If we are right in assigning the great sandstone series of the 
Uinta to this member, it would have there its maximum development, reach- 
ing, according to our observations, 12,000 feet, or 14,000, as displayed in 
the cation section observed by Powell. 

In the Uinta body are numerous intercalations of groups of shale, con- 
sisting of seven or eight members separated by sandstone strata. Some of 
these shale and clay beds, notably one at Gilbert’s Peak, reach a thickness 
of 100 feet. Taken as a whole, a variety of chemical studies of the Weber 
quartzite would indicate that it had an average of 70 or 75 per cent. of 
silica, the remainder being made up of alumina, lime, and alkalies. Like 
the great Cambrian series, it is a compressed body of what was originally 
arkose sediment. In the intercalated clays and in some of the quartzites 
are slight developments of muscovite. Conglomerates are not uncommon. 
Toward the summit of the series, and always in the easterly exposures, 
the included pebbles are rounded, but over a considerable part of Nevada, 
where the series approaches the western limits of the Palaeozoic area, there 
is, toward the middle of the group, an enormous development of conglom- 
erate, made up partly of rounded pebbles and prominently of sharp, angular 


RECAPITULATION OF PALAOZOIC. 241 


fragments of jasper or chert, and occasionally of crystalline schists, held to- 
gether by a saccharoidal matrix of quartz and feldspar grains intermingled 
with carbonate of lime. When comparing the thicker body of the Uinta 
with those of Utah and Nevada, it will be seen that the beds are in a much 
less compressed condition. In the Uinta, especially throughout the easterly 
part of the uplift, the series is made up of what would be called indurated 
sandstone. ‘Toward the west end of the range, especially in the low hori- 
zons, the sandstones are compressed into quartzite, while over the greater 
part of Utah and Nevada the group is consolidated into a dark quartzitic 
type of rock. 

The next conformable member of the series is the Upper Coal Measure 
limestone, a body about 2,000 feet in thickness, which, over all of the Great 
Basin country, is prevailingly made up of lime beds of light-gray or drab, 
mingled with dark-gray and dark-blue beds. In general it is thinly strati- 
fied, frequently subject to local impurities, and from bottom to top well 
charged with fossils of the Coal Measure group. In the region of the Uinta 
it has about the same thickness, but between it and the Great Basin devel- 
opment there is a wide physical difference. In the Uinta the base of the 
series is composed of the dark-gray limestones, and the middle and upper 
portion for not less than 1,200 feet is made up of remarkably variable inter- 
calations of calciferous sand rock and thin shaly and limy beds, the whole 
capped by a development of cherty limestone from 100 to 150 feet thick, 
characterized by an abundant presence of the genus Bellerophon, from which 
it was called by Powell the Bellerophon limestone. Between the Weber 
quartzite and the Upper Coal Measure limestones over the Great Basin and 
in the Wahsatch there can be no question of an absolute conformity. In 
the region of the Uinta, between Professor Powell and ourselves there is a 
difference of opinion as to this relation. Powell holds that, although they 
are conformable in angle, he has discovered a nonconformity of erosion, 
meaning by that that the surface of the sandstone series had been eroded 
into hills and bluffs, over which, with no difference of angle, the limestone 
beds were deposited. Having frequently examined the Uinta throughout 
its whole length, we are of opinion that this nonconformity is illusory, and 


that the apparent discrepancies can be accounted for by the effects of per- 
16K 


242 SYSTEMATIC GEOLOGY. 


spective in observing outcrops, and by the wonderful series of faults which 
accompany the Uinta uplift, often bringing the upper limestones down into 
contact with quartzites far below the top of the latter series. 

Of the limestone body which forms the chief Paleozoic development 
in the Rocky Mountain region, fully six tenths are charged with Coal Meas- 
ure fossils. This thousand-foot limestone has only yielded one fossil outside 
of the range of the Coal Measure species, and that was a Waverly form 
obtained in the Black: Hills near the base of the series. It is therefore 
probable that the Weber sandstone is entirely wanting in the Rocky 
Mountain region, or is represented only by the siliceous impurities which 
have been noted near the middle of the limestone. It is further certain 
that the greater part of the lime body belongs to the Coal Measures, and 
that the single Waverly species indicates a horizon corresponding to the 
lower part of the great Wahsatch group. The Minnelusa sandstone of 
Winchell, which has not been re-observed by Newton in his more extended 
study of the Black Hills, seemed to occupy the position of the Weber, but 
it does not appear in later accounts of the geology of the Black Hills. 
With the Upper Coal Measure limestones the Paleozoic of the Great Basin 
comes to a close. 

The following list of fossils gives the species collected from the Upper 
Coal Measure limestones above the Weber quartzite : 


Busting cylindrica, Wischer: +2. 1 sss. oats asaaoe eee ee eee ae a 
Busing ne spyi(very lated) aces aoe ee oe eee anes | 
Fusiling sp.? (minute)... 22222. 2 aee = -Ss See  e i 
Syringopora multattenuata, McChes.........---------------------- 1 
Lithostrotion. W hitney?, Meek . 2.22. 2 22-50 s 2st ee See ee 1 
Zaphrentis Stansburyi, Wall. 22203 72 Sas .cee eee eee te ere 1 
Orilas carbonarta, Swallow.22 2220-2. 3-2 > 6s sane see eee eee 3 
Streptorhynchus robusta, H.---.-------- SER Da ET ee ane eae ns 1? 
Streptorhynchus crassus, Meek & W...-..-:.-2---2 2-22 -----22 4 
Meckella striata-costata, Swallow.- =. «2 === Sas52ses-2- ee oe 1 
Chonetes' granulifera, Owen 22sec teak 2 ae a ee if 
Productus longispinus S0We2- 522 +38 Sor ee eee 1 


Productus multistriatus, Week .. 2.2. 2.52222 ao see oe te 2 


RECAPITULATION OF PALZOZOIC. 243 


PV OUUCLUS INCU ASCENSISY Mam mer ee eee =o. 5 2 22. ete eles Se See 2 
IPT OOUCIUS PVOMCHIANUSS NOP Me nae s ess on sta ete Se Ly Lay 5) 
ERODUCTUS SDUNCLAUUS Marie tae oe 228 see 2 See ci Se Le old 2 
Producius punctatus var. Rogerst, N. & PB... 2.2.5. .62 eee eee 2 
eroductusssemicucuiaius., Marts. 22 2) 2000. seo ook ee ee ee 5 
ET OMUCUES: SYMMEMGUSH MIG CHES. As\s's Soc oe te ok. Sons Sieee 2c bes 1 
SUNT Cn Gd COMCNALIM MOM. 8 faye See ee OS ei aaa di 
SHOVEL G OUlonlecdimpetally 9. 8 7 vee. Scns cee hein seam Sais as 1? 
Spirifera Rockymontana, Marc., sp. opimus, H.......--.---.--. ------ 3 
Srrvjerasp, resembles sp. lorbest, I.) a0: 2222s sa5 sees 45 eee 2 
SUE CT UNCP IM CNLNCKENS(S GONUMISS ee: se ee ieee ee ee ere eee 1 
SPUTISCriNde DULCIT Oe MCG Ks nee Sekt ee eee eee ee eo 4 
JW OT UTAES UBD Aais. I EN ge eg e egeEe  e e e e 3 
MMC Ia PUNCH CVG, OOUM. 2222 2e a2 5 oe os eee es ob cee ee il 
PANINI SES UULEL ICG n tie letra se Le Poe Sie ee se SoS p58 i 7 
PAIL MU MESHICOTSSUB evar tT eetars fe ee RN as eS oe ee aia eRe ere SB 1 
LG YUCRONCHOLU LON. Manel: 3 ooo eaea co aces sna ot ee ae ee 1 
IACONO Oem NICO Nessa ets toy: ee ae ee Se ee eS 2 1 
PNEECUCI OMS [I omens ate Sa emcee or LN Oy oh ge te ps 1 
INEECHLONOADCIISIViOLGs SLOVONS —S2 22. 2 Soc) loc.ko2 52 ese ne oa sae 1 
ISCOQLOIEKHE a CONCAUGT CO ua” Sm enae ra tai c ee ae 1 
icurophorus oplongus, Meeks = 0. 222 fs sete cece se ce nee eeetese 1 
ICO USICUN TUS eC OKs te area etek ce Se yet ee ee 1 
INCA CICS, ST0e Ce vee iy oN ne ay eR fs RA PTs Pte eek oe 4 a 1 
Bellerophon carbonaria, Cox? (broad bands)......-..-.....-.------ 2 
EHELONNOW SP. t: (SMOOUNLSP)) elses) wES oe Seed Boo Ue. 2 
OrtROCeras: CreUurosinn, CeUNitZ aio <5 oe ce iain ows space eee ee aS 1 


-The following is a list of species recognized in the upper beds, but not 
found below the Weber quartzite : 


Buslimearcylindyica, PIsCher= <j. oso e's ote seboactadle ec biceu sce 1 
TE YTEL SU SUNS Ae oo oS OO eR Ee ea il 
DESIST ISN. 5 8 OST Eg a 1 


244 SYSTEMATIC GEOLOGY. 


Meckella striata-costata, Swallow .- « « -<..< <2 52-3 see erate 1 
Producius sub-horridus, Meek... ..... .2.2.--,2.2 + sees ae es ee 7 
Productus punctatus var. Rogerst, NP... 2 ee ae oe ee 2 
'Productus longispinus, SOW. - -o2 2-2 ee ee 1 
Spirifera, resembling sp. Forbesi, H. (a Lower Carboniferous species) - 2 
Spirifera octoplicatus, Hall? (identification doubtful)......-.--.--.--- 1% 
Snirverima..puichia,, Meek 2, — 2,2fce gee ee es es 4 
Humetria punctuliferd, SUM, e232 cere ee fee 1 
Athyris. Roissywn «(fragments guilty et sors ct ee e e 1 
Riynchonella Utah; Mare Sees os oe kee eee en ee 1 
Nitoula pond: MG CW Gs so eaters yes eee pee ee ee ee i 
NUCULGBIN, Ts <5 ext yea Peete ote 8 ee 1 
Nouculonahellsiviata, Stevens) 14 ase o See ee eee 1 
CHOU Chia 2. CONCHUA A MIGCK yee eee oe eee Sole ae eee 1 
Schizodus cunts, Meek ay 2 Ae Seer ee ee ee 1 
NGGdies 80 os 5b. atte Sa ee eee Cee ee eee 1 
Delleronuon Car bonaris, OX 12. Be oa ee ee eee 2 
BelerOpnow spd. o\sc iutind a doa es id oe a oe ee eee 2 
Orthoceras crebrosum, elnita as... 20a ee eS 1 


The Wahsatch limestone yields the following species, not recognized 
in the Upper Coal Measures : 


Zaphrents cxcentrica, Meek: «- 2.22222 scene 2tsno5 oe yee eee 1 
Zaphrentis sp.? (resembles Z. centralis, Ed. & Haime).-....-------- 3 
Lophophyllum proliferwum, McChes...-.-.........----------------- ih 
Cyathophyllum (Campophyllum) Nevadensis, Meek.........-..------- 1 
Archiocwdoris NES). ¢ 222 2 xs see ee ee eee 1 
Sweproriunchus erenistria, Phil. 225222 sieee = eee = 2 
Productysicora, DiOrbist a2 SS5uF Ss Seek Sy ee ae ee tes i 
Producius pertenuis,, Meck. 2... 2.2 25 See ee ee 1? 
Ithynchonetla Osageisis,. Swallow... 422-2 2.2242 see eee eee 1 
Terebratula bovvdens, Morton. ocean. Soe aes a ee ee 2 
Cardiomorpha Missouriensis, Swallow......--..---..--..--------- i 


RECAPITULATION OF PALAOZOIC. 245 


GOniatites, TOU: anette Te A fec(o es aaa ee oe il 
CY LOCEV Si COSSOLO I eee ot ts gs ee! Soo fae oe Ne ee ayia ete pate 1 


The followimg forms are common to both limestones : 
Lower. Upper, 


Syringopora multattenuata, McChes........--.-------------- of 
AUpnrencisisiansouryy, lal. 25. 2 cuss sees oe) eee ee Sees 4 1 
Lnthostrotion Whitneyi?) Meck. .:....- <.-..--- + --00-2--5----- Byte Ly 
Sirentorhynchus rovusius: Ela? - sce cc 2 Se ae toe 1 1? 
Sireptorhynchus: crassus. Meek © os 222-6 32.5% 92 = ce es oe 1 4 
Chonetes gramuliferd, OW ems ao ne enacts ine pe ene 4 1? 
Productus Nebrascensis; Meek ...:..... i. ...-----2--226-+--0---- 2 2 
TER OUUCIUS a DUNELLIUG wy MOP Gs ia oa 2h 32 spe er he, = eee s.cre es 2 2 
Productus prattenianus, Norwood....-.---:-+-.------:----- 3 
AROQULCLUS SCNUINCLICIUGLUS ML. a. = ent k= 2 o-oo he ec Ah es 6 5 
Progucius symmetwicus, McChes:... ..2-5-.- .---7-2--+4-2-5--- 4? 1 
Spiriera.camenata. WUOXtON,= 21. t- 46-2 c cee 2c) 2-8 oe =) 2 if 
Spirifera Rockymontana, Marcou: .--:-.:-=-+.----.+-~--2--- 13 3 
ManUnianlincaiast Marts. <2.) 2 0 Fee cue ccs eee eet oe eke 4 3 
Spiriferina Kentuckensis, Shum........--.----:22:---<----- 1 1 
PANDY TISESUOLLO MINA nats © Siegen Sod ee SoA te ee eee 5 7 


In the Wahsatch, in the Uinta, and at the little Rawlings Peak expos- 
ure was observed a series of argillaceous and calcareous shales with muddy 
marls overlying the Upper Coal Measure limestones, the whole reaching 
about 650 feet in thickness, and carrying from summit to base the follow- 
ing characteristic Permo-Carboniferous fossils : 


Aviculopecten curtocardinalis n. sp. 

Aviculopecten McCoyi, Meek. 

Aviculopecten sp.? Meek (Pal. Up. Mo., plate IL., fig. 10). 
Aviculopecten occidaneus, Meek. 

Aviculopecten parvulus n. sp. 

Aviculopecten, sp.? resembling Pecten Clevelandicus, Swallow. 
Aviculopecten Weberensis n. sp. 


246 SYSTEMATIC GEOLOGY. 


Eumicrotis Hawni, M. & H. 
Eumicrotis sp. undet. 

Myalina permiana, Meek. 
Myacites Weberensis, Meek. 
Myacites aviculoides, Meek. 
Myacites inconspicuus, Meek. 
Schizodus sp. = S. ovata, Meek. 


In the region of the Uinta and at Rawlings Peak the shales are 
compressed to a thickness of about 300 feet, but in the section of Weber 
Cation, where most of the fossils were obtained, the full 650 feet is observed. 
At the Uinta and at Rawlings there is no appreciable nonconformity between 
the Permian and the Coal Measure rocks; but at the Wahsatch, as already 
described, there seems to be a slight discrepancy. It is curious to note the 
difference in the character of the uppermost sediments of the Upper Coal 
Measures in the Wahsatch and elsewhere. As seen everywhere else, the 
horizons immediately under the Bellerophon limestone are all interca- 
lations of sand and lime, but in the Wahsatch they are fine argillaceous 
shales, characterized by wonderfully fine ripple-marks. 

The Permian is a shallow-water, ripple-marked, argillaceous deposit, 
appearing east of the Wahsatch. 


In the whole Paleozoic section there are 18,000 feet of siliceous sediment, 
13,000 of limestone, and about 1,400 of slates and shales. The general ab- 
sence throughout the Coal Measure horizons of beds of coal, and the equally 
conspicuous absence of shallow-water deposits, indicate that the whole great 
Paleozoic series was from the first received on the bed of a deep ocean. 
The sole evidences of littoral or shallow-water depositions are in the occa- 
sional sheets of conglomerate which are seen in the siliceous members and 
in the slight development of coaly matter near the top of the Wahsatch lime- 
stone in middle Nevada. When it is remembered that the configuration of 
the ocean bottom was accidented by enormous Archean ranges whose peaks 
towered up to the levelof and abovethe highest Paleeozoic deposition, it will 
be seen that the conglomerate beds might easily be formed from the local 
degradation of the island masses themselves. Doubtless these mountain 


RECAPITULATION OF PAL OZOIC. 247 


slopes contributed largely to the fragmentary materials of the Paleozoic 
series; but, on the other hand, there are greater arguments for supposing 
that the vast bulk of the detrital sediment entered the ocean from the west. 

Considered as a whole, the Palzeozoic series thickens to its western limit 
on longitude 17° 30’. West of that meridian there is a sudden, remarkable 
change in the whole geology. No more Palzozoic rocks are observed in 
Nevada, and in California only inconsiderable deposits of Carboniferous. 
Over the whole basin of Nevada the oldest post-Archean rock is the 
Trias, which lies directly upon the old Archean mountain slopes, without 
any interposition of Palzozoic beds. It is immediately evident that the 
Palzeozoic never extended over that region; in other words, that western 
Nevada formed during Paleozoic time a continental mass which bounded 
the ocean in that direction, and whose continued degradation furnished the 
greater part of the sediment that was spread out on the sea-bottom. When 
viewed from our latitude to the south, from the observations of other west- 
ern explorers, it is evident that the Palaeozoic series as a whole greatly 
diminishes in that direction. Northward, in Montana, the observed thick- 
nesses are quite inconsiderable as compared with those of the region of the 
Fortieth Parallel. The rocks of the Salmon River Mountains and Blue 
Mountains of Oregon and Idaho have not been sufficiently studied to 
indicate definitely whether the Paleozoic series also thins in that direction ; 
but from the scanty data now known it would seem that the area of this 
Exploration has opened up what was the region of deepest ocean and most 
extensive sedimentation. 

On the next page is a tabular statement of the Paleozoic strata in 
Utah and Nevada. 


SYSTEMATIC GEOLOGY. 


248 


WAHSATCH SECTION, 32,000 feet conformable. 


PALHOZOIC SUBDIVISIONS. 


WAHSATCH AND MIDDLE NEVADA. 


CARBONIFEROUS, 15,000 feet. 


Waverty, 


DEVONIAN, 
2,400 feet. 


Permian, 650 feet. Clays and marls and limestones, shallow. 
CesEt pes Blue and drab limestones pass- 
MU e  R ESL OZLCS ing into sandstones. 
2,000 feet, 


Weber Quarizite, 
6,000 feet, 


Compact sandstone and quartz- 
ite, often reddish, intercalations 
of lime, argillites, and con- 
glomerate. 


Wahsatch Lime- 
stone, 7,00o feet, 


limestone, with siliceous ad- 
mixture, especially near the top. 


Ogden Quartzite, 1,000 ft.| 


SILurian, 1,000 ft. 


Ute Limestone, 1,000 ft, 


CAMBRIAN, 12,000 feet. + 


Cambrian Sili- 
ceous Schists, 
11,000 feet. 


Cambrian Slates,800 ft. +-| 


Pure quartzite, with conglomerate. 


Compact or shaly siliceous limestone. 


MIDDLE NEVADA SECTION, conformable. 


CARBONIFEROUS, 15,000 feet. 


Upper Coal Meas- 
ure Limestone, | Heavy blue and gray limestones. 
2,000 feet. 

Weber Quartzsite, | Quartzite, with, near the middle, 


6,000 feet.+(?) 


angular conglomerates. 


Waksatch Lime- 
stone, 7,000 feet. 


Varied gray and blue limestone, 
often heavily bedded, drab in 
the Devonian horizon, 


WavERLY, 
Devonian, 
2,000 feet. Ogden Quartzite, 1,000 ft. 
Srvurian, 
2,000 feet. Pogonip Lime- 
stone, 4,000 feet. 
Cambrian 
, Quartzite. 
z ar 
z 
a 
= 
< 
ie) 


Pure and fine-grained. 


Saccharoidal blue and gray sili- 
ceous, sometimes shaly lime- 
stone. 


Compact quartzite. 


ag ee ae ee - - cy an 


= 2 
cs : 
Dire. f a 


TE 


AL MAP OF 


ARCHAAN, G@ 


we 


‘ 
2 


camper lll 


Ke 


‘ 
t 


TE (OUL,O)'C 


1 
a 


cows 


AGSUMIL YE TCA, C 


a Nah 


ee 
Wi 


=e 
SD) 
Shi] = 
g | | 
5 | | 
: 
| 
| 
| 
2 | | 
| 
3 
% ] 3 § 8 


Re sne 


DAM NG2 ONVAMEMOUN, (Oe AMEHe I OURMIN NE, Tis IPVAIRVATLAG, Jef IL; — TIL. 


PALEMOZOIC EXPOSURES. 


or, 


poe 


BS 


= —~ 
eg 


=A 
b=? 


2 
< 
a 


= 


Sa 


a WN a2 


oN 


Vs 
EZ 
Sacet 
le z£ 
i= rat 
A se ANS) 
When 
Ga 
XM) 
VW Nicae 


So! we =f) 


one Inch 


CARBONIFEROUS 


Ee] SUBSGARD OC ee Es UPPER COAL eS 
DEVONIAN LOWER COAL MEASURES WEBER QUARTZITE PERMO-CARBONIFEROUS | LJ 


CHAPTER IV. 
MESOZOIC. 


SECTION I.—TRIASSIcC.—ROCKY MOUNTAINS—UINTA RANGE—WAHSATCH RANGE— 
PROVINCE OF WESTERN NEVADA— WEST HUMBOLDT RANGE—PAH UTE RANGE— 
HAVALLAH RANGE—FISH CREEK, AUGUSTA, AND DESATOYA MOUNTAINS. 

SECTION II.—JuRASSsIc.—RoOcKY MOUNTAINS—UINTA RANGE—W AHSATCH RANGE— 
WESTERN NEVADA. 

SxcTion IIJ.—CRETACEOUS.—DAKOTA GROUP—COLORADL GRoUP—Fox HILL 
GROUP—LARAMIE GROUP. 

SECTION IV.—RECAPITULATION OF MESOZOIC SERIES. _ 


SC LLON 
TRIASSIC. 


Rocxy Movuntains.—Directly overlying the Paleeozoic limestones, in 
conformable superposition, and not infrequently overlapping the Paleozoic 
and coming directly into nonconformable contact with the Archean, appear 
the well known Rocky Mountain Red-beds, which from their position be- 
tween the Coal Measures below and the well recognized Jurassic beds 
above, have been generally assigned to the Triassic age. Reserving all 
discussion of the validity of this assignment to later pages of this chapter, 
it is proposed here to give simply a brief statement of their physical 
condition and continuity along the flanks of Colorado Range within the 
field of this Exploration. From the lower limit of the map, nearly up 
to the 41st parallel, the Red-beds lie directly upon the Archean, and form, 
with their soft, friable strata, a remarkable contrast with the adjoining 


crystalline rocks, the Red series varying in thickness from 300 to 850 feet. 
249 


250 SYSTEMATIC GEOLOGY. 


It is interesting to observe that where they are in direct contact with the 
Archean rocks, they have a dip rarely exceeding 15° and often retaining 
an approximation to the horizontal; while to the north, where erosion 
has been deep enough to reach and uncover the Palzeozoic series, the dip 
increases to the vertical, with exceptional instances of slightly reversed 
position. The region of contact between the Trias and the Archean affords 
an interesting display of the mode of deposition of the coarse, friable gravel 
and sandy material of the Trias upon the hard irregularities of the crystal- 
line series. 

The beds along the southern limit of the map, bordering the Big 
Thompson and the Cache-la-Poudre, attain a thickness of 800 to 850 feet, 
thinning thence northward and reaching a minimum in the region of Horse 
and Lodge-Pole creeks, where they scarcely attain 300, but thickening 
again in the region of Chugwater and Bush creeks to nearly 700 feet. 

On the western borders of the range, the conditions thus sketched are 
repeated. North of the Union Pacific Railroad, the soft, easily eroded 
beds of the Trias, varying from 400 to 800 feet in thickness, rest directly 
upon the uppermost limestones of the Coal Measures. South of the rail- 
road the Trias overlaps, and, as on the eastern side of the range, comes in 
contact with the Archean. Here, within the great bend of the Laramie, is 
a broad triangular region, fifteen miles on a side, in which the Trias pos- 
sesses only a very gentle dip from the Archzean, in many places resting 
truly horizontal. The dip upon the western side of the range is always 
gentle, from 4° to 10°. South of Red Lake there is an exposure of at least 
700 feet, while directly west of Laramie City there cannot be more than 
400 feet. At the Chugwater there is about 600 feet, with very heavy red 
sandstones at the bottom, interrupted by occasional fine conglomerates, 
these overlaid by finer red sandstones with interstratified beds of red clay ; 
these, again, by red shales, overlaid by compact, arenaceous limestone 
strata, three or four feet thick, followed by fine red sandstones of rather 
thick bedding, and a second seam of bluish-white cherty limestone from six 
to ten feet thick, the whole capped by heavy, reddish-yellow sandstones. 
At Box Elder Creek, where the section is about 650 feet in thickness, are 
displayed, counting from the base upward — 


TRIASSIC. 251 


1. Coarse red sandstones with conglomerates, equivalent to the vi 
lower members on the Chugwater.-.....-..-------------- 100 

pe Massive SAMUStONGS == oo sepa taea a eae alte nee cia sai 300 
. Yellowish-red sandstones, with variable bedding and texture. - - - - 100 


2 

3 

4. Laminated red shales, with some red clay -.....-------------- 

hee hhingbedcon wlio limestone... 222... a < <feo ie jee alee 

6. Fine-grained, earthy, crumbling sandstone, pink and red, with lay- >; 150 
SOA Ui Be PON meee ees ao ese or eee ee 

tegveddish-vellowssanstone 202 = erie ei ss ee se 


In the region of the Big Thompson, where the greatest thickness on 
the flanks of Colorado Range is exposed, the series consists of heavy beds 
of coarse and friable pink and brick-red arenaceous material, partly inter- 
rupted by conglomerates, partly so coarsely gritty as to conceal the trace 
of bedding, and partly again thickly accumulated strata of brick-red sand- 
stone, the middle region interrupted by red shales and clays, the whole 
closed by a series of pinkish, pinkish-gray, and yellowish-gray sandstones, 
the upper members containing several beds of pink and white gypsum and 
blue limestone. 

Taken as a whole, and with the exception of the gypsum and lime- 
stone beds, which nowhere within our field of observation exceed forty 
feet in thickness, it is essentially a sandstone series, for both clays and 
shales are exceedingly arenaceous, and the dominant color is a brick-red 
for the lower half of the series, and variable lighter reds, pinks, and yel- 
lowish reds for the upper half. While this division of color holds good 
in general, it is often varied by extremely brick-red, almost vermilion- 
colored beds appearing near the top, and light ones intercalated in the 
region of the heavy red lower strata. The position of the narrow blue 
limestone beds, as well as that of the gypsums, varies through the upper 
half of the series. Next to the red color, the most noticeable feature is a 
remarkably sharp, persistent cross-bedding, developing very fine flow-and- 
plunge structure with the most remarkable arrow-head sections, which is 
observed in the upper horizons, where the bedding appears heavy; but 
never, so far as we have observed, among those beds which come into im- 


252 SYSTEMATIC GEOLOGY. 


mediate contact with the Archean. Zones of conglomerate in general are 
either confined to the lower members of the series or else to the near neigh- 
borhood of the Archean. The pebbles are rarely very large in this mate- 
rial, and are almost all siliceous. Besides the several well defined limestone 
beds, a few of the horizons of the upper and impure sandstones appear 
highly calcareous; rocks which in hand specimens would never be supposed 
to contain lime, giving a brisk effervescence when treated with dilute acid. 

A typical specimen of the red sandstone taken from the upper members 
of the Trias, near the entrance to Big Thompson Camon, is a fine-grained, 
friable rock, deep-red, with a laminated, almost shaly structure. It was 
subjected to chemical analysis, the results of which will be found in the 
table of analyses of sedimentary rocks. The analysis shows, besides the 
siliceous and ferruginous material of the normal sandstones, the presence of 
an unexpected amount of soluble carbonate, including some dolomite, with 
an inconsiderable mixture of arenaceous material. It is noteworthy that 
no sulphates are detected, although the formation immediately in the neigh- 
borhood bears beds of quite pure gypsum. Below these shaly beds occur 
deep-red strata, having a coarser grain and no traces of the lamination 
characteristic of the last-named specimen, which upon being treated with 
acids gave no indication of the soluble carbonates. 

Laminated red shales, from a horizon near the top of the Trias on 
Horse Creek, and interstratified between coarse sandstones, were found on 
examination to contain an amount of calcareous matter equivalent to that 
of the Big Thompson, together with a similar amount of dolomite. The 
narrow beds of limestone already noted occur sharply defined from the 
enclosing siliceous material. Under the microscope they of course do show 
a considerable percentage of angular quartz grains, but they are almost 
wholly of dolomitic limestone. In the region of the Chugwater they occupy 
a horizon very near the top of the Trias, the lower bed consisting of a some- 
what cherty material, and the upper of a characteristic bluish-white, sili- 
ceous dolomitic limestone. These limestone beds, although outcropping at 
intervals all the way from the Big Thompson to the Chugwater, do not 
seem to possess any considerable continuity, but occur at or about the same 
horizon at irregular intervals. The indications are that there were cessa- 


TRIASSIC. 253 


tions of deposition of the siliceous material, and that the calcareous deposits 
were not in continuous sheets, but were gathered by the oceanic currents 
into limited areas, which in turn were buried by the succeeding sand-strata. 

Gypsum deposits characteristic of the red Triassie beds occur chiefly, 
if not altogether, in the upper half of the series, their irregular, lenticular 
masses occurring, as do the limestones, at intervals. The gypsum beds vary 
from two to twenty-five feet in thickness, the heavier masses occurring with 
a broad bedding, and thinning out from a point of maximum thickness in 
every direction. The sulphate occurs both massive-granular and highly 
crystalline, varying in color from a pure, dazzling white to a pinkish shade, 
according to the amount of ferruginous impurities. In general it appears 
as a streak of creamy whiteness in the bright red sand-strata, streaked 
and stained into a variety of pale pinkish and yellowish-pink shades. From 
the interesting locality at Red Valley, near the northern end of Laramie 
Hills, a specimen of gypsum gives nearly the characteristic formula, the 
analysis yielding — 


Sulphatewotelimene) Met cae ee eae oe ee (komtlal 
\ISEER Gy OE cola e, Nk AS Re rah ae tA ct ela an 21.21 
SPIN EE le opener ey ane, Sere a nee eae 99.32 


The Red-beds of Colorado Range have thus far yielded to our search 
no organic remains, saving obscure pieces of half-petrified, half-carbonized 
wood, which crumbles on exposure to the air, and displays no characteristic 
structure. The following are some of the more noticeable localities along 
the eastern base : 

Wherever along the eastern base of Colorado Range the strata of the 
ielined sedimentary series extend for any considerable distance westward 
toward the heart of the range, they are found to occupy an approximately 
horizontal position, showing that the rapid change of dip occurs very close 
to the eastern belt of foot-hill beds. An example of this rule is the 
recurve around the head of the Chugwater; but at the head of Bush Creek 
the upper valley, above the region of the Pliocene conglomerates, is occu- 
pied by a shallow basin of Trias, which rests, almost horizontally, directly 
upon the granite. The valley surface is entirely made up of the gypsiferous 


254 SYSTEMATIC GEOLOGY. 


upper portion of the Trias, a large part of the basin being covered with 
irregular outcrops of gypsum. The strongest bed observed is about fifteen 
feet thick, of clear, pure-white sulphate, only stained by the contact with 
ferruginous enclosing rocks. 

Around the Chugwater promontory outcrops a Trias curve, standing 
at very high angles, with a rapidly varying dip. The beds slope from 61° 
to 55° on the north-and-south lines, and only 25° where they reach an 
east-and-west trend. 

In the region of Lodge-Pole and Horse creeks, where the beds stand 
at an extremely high angle, they are more compact, fine-grained, often 
shaly, with a great appearance of argillaceous material, the colors being 
deep red and reddish yellow. As with the underlying beds and the over- 
lying Cretaceous in this region of high dip, the whole series is actually 
thinner than where its inclination-angle is much lower, and this can hardly 
be due to a local thinning of all the conformable series. It is rather refera- 
ble to the shrinkage due to unusual disturbance and compression. 

Whoever has examined the slightly compacted modern sea-sands made 
up of the débris of marine Pliocene, especially when placed under the 
microscope at a low power, cannot fail to remember the large amount of 
interstitial space between the particles of quartz, sand, and sea-shell. It is 
evident from such observations that rough sandstones can lose fully forty 
per cent. of their volume without any compression of the quartzy material. 
In the more compacted sandstones the interstitial space is either entirely 
made up of infiltrated argillaceous and ferruginous matter, or obliterated 
by pressure. In the case of the older quartzites, the Cambrian particu- 
larly, the outline of the original granular quartz may often be traced, flat- 
tened to a long, lenticular form. In the case of the Archean quartz- 
ites, the figure of the original particle is altogether lost, and the entire 
mass shows a confused cryptocrystalline structure. It is not strange, 
then, that a series of beds exposed along a line of 100 miles, as is the 
Trias east of Granite Ridge, should suffer very great variations of thick- 
ness: first, from an irregular depth of original deposit; secondly, from 
the factor of compression. It is assumed to be a rule that in all cases 
of extremely high dip the volume of each member of the sedimentary 


TRIASSIC. 255 


series is distinctly less than in cases of low dip; and the physical condi- 
tion of the rock is itself an evidence of this compression. Accordingly, 
when the gently dipping Trias sandstones of the Big Thompson region 
are compared with those near the head of Horse Creek, the dip, thick- 
uess, and actual petrological compactness are found to vary correspond- 
ingly. 

South of Box Elder Canon occurs another instance of a westward-ex- 
tending overlap of Trias resting directly in a depression of the Archzean 
in a nearly horizontal position, only dipping from 2° to 4° to the southeast. 
In direct contact with the granite is a considerable bed of reddish-gray 
conglomerate, overlaid by massively bedded red sandstones. This bed was 
nowhere recognized to the north, where it is possible that the Carboniferous 
always lay between it and the Archean, and the occurrence here is due 
to the immediate neighborhood of the Archean mass. 

From the Cache-la-Poudre to the southern edge of our map the forma- 
tion rapidly thickens and becomes correspondingly looser in texture. The 
series is defined in outcrop at the upper limit by the persistent, trough-like 
depression which separates the red Trias from the hard Dakota sandstone. 

On the Big Thompson the upper part of the Trias is characterized by the 
presence of several thin sheets of limestone, and in general the transition into 
the Jura is marked by a calcareous passage-member, mixed with varying 
sheets of sand, the whole having a thickness of about fifty feet. In this 
region the gypsum bed is about twenty-five feet thick, of nearly pure white 
erystalline-granular sulphate, interbedded with dark-red sandstones. 

The extremely gentle dip of the sedimentary formations on the western 
flank of the Archean mass of the range, renders the final surface, when 
beveled off by a uniform erosion, remarkably free from bold outcrops, so 
that the junction between the underlying grayish-blue limestones of the 
Upper Carboniferous and the Trias is often only discoverable by the change 
in the color of the earthy deposit which masks the more solid edges of the 
beds. Here and there at intervals are the limited escarpments of the red 
sandstone beds, with their bluff faces toward the range. At Red Buttes, 
near the Pacific Railroad, are the best exposures of the sandstone to be 
seen on the western slope. For some distance to the east and north of 


256 SYSTEMATIC GEOLOGY. 


the railway station the sandstones, marls, and clays have been eroded by 
the local streams, showing cliffs and buttes which reach 100 feet of vertical 
exposure. The basal sandstones of the series rest directly upon the bluish 
and yellow Carboniferous limestones. These lowest Triassic beds are here 
rather pale reddish-yellow, and are characterized by the development of 
concentric red spots. They are formed of distinctly visible grains of quartz, 
held together by a calcareous and marly cement. There are several zones 
of pebbles, and the whole series is prevailingly and characteristically red, 
up to the very base of the Jurassic. 

South of the railroad the Triassic beds still maintain their gentle dip, 
and in the region of the track overlap the Carboniferous and pass into 
direct contact with the Archean. It is a noticeable fact that the Laramie 
Hills, or northern part of the range, are separated from the more elevated 
portion to the south by a depression marked by the northern waters of 
Cache-la-Poudre Creek, the pass extending across the whole range in a 
northwest-and-southeast direction. This continuous depression terminates 
on the western side exactly where the Trias overlaps the Carboniferous, 
while the eastern end of the depression comes at the head of Box Elder 
Creek, where also the Trias overlaps the Carboniferous and in a similar 
manner comes in contact with the Archean. This, to my mind, would 
suggest a pre-Cambrian displacement here which has depressed the whole 
northern part of the range, the depression making itself chiefly felt along 
the eastern base of the northern half. 

South of the railroad, on the western side, the contact of the Trias with 
the Archean is rather interesting. It is seen gradually to overlap the gentle 
inclinations in thin beds, and to abut squarely against the steeper slopes 
of the Archean. In general, it dips gently away from the Archean, the 
Trias ridges being defined by the harder beds which have protected from 
erosion the softer and more shaly portions below; and wherever there are 
lines of erosion parallel to the contact-line with the Archzean, the steeper or 
more escarped faces are turned toward the range. 

Gypsum deposits are well shown north of the Willow Creek and 
North Park road, where they occur through a thickness of at least 80 or. 
100 feet, and are interstratified with dark, intensely red sandstones. 


TRIASSIC. 257 


South of the road are some remarkably eroded forms suggestive of ruined 
cities. 

West of Antelope Creek the Trias extends twelve miles to the south 
of the Wyoming and Colorado boundary, filling a bay-like depression in 
the Archean body. Here are exposed, along the eastern side of Laramie 
Valley, 1,200 feet of beds having a very slight dip to the north and west, a 
high, abrupt wall of nearly 1,000 feet presented toward the plains. Upon 
the front of this escarped precipice may be seen the interstratified marls 
and limestones of the Jura, overlying the heavier red gypsiferous beds of 
the Trias. In contact with the Archean body, the sandstones are of coarse 
ash-colored materials containing angular fragments and rounded pebbles, 
with more or less calcareous matter in the cement, followed by a hard, thin, 
cherty limestone, which passes up into reddish-gray sandstone, and above 
this the usual beds of coarse red sand, with numerous red clay beds, 
varyingly shaly, which give a prevailing argillaceous character to a wide 
zone of the sandstones. Within this red argillaceous series are thin beds 
of pure clay and white gypsum, the latter varying from two or three 
inches up to several feet, with one solid body of twenty-two feet enclosed 
between two series of intensely red, dark, indurated sand-rock. Above 
this gypsiferous zone occur heavy red sandstones, which pass through yel- 
lowish friable beds with marly intercalations into the calcareous beds of 
the conformable Jura. 

The following section illustrates the chief features of the Triassic 


series, as displayed here, beginning at the summit: 
Feet. 
1. Yellowish-red sandstone, passing down into fine, deep-red, evenly 


bedded, strongly coherent sandstone .........-----.--- 375 to 400 
2. Argillaceous shales and argillaceous sands, with interstratified layers 

of fine, pure clay, the whole prevailingly red, with grayish and 

yellowish-red zones carrying four or five beds of gypsum, one 

reaching twenty-two feet in thickness; in all..-......-....-- 150 
3. Red compact sandstones, beds of varying thickness, some coarser 

inal SlOvonS) Seba eT a oe Eryn ee ee ee 250 
4. Reddish-gray sandstones carrying a bed of cherty limestone four 


On Nye dteottnick-sthe whole .coo so. c}. 2 ae hie i schencexe eect 175 
17 Kk 


258 SYSTEMATIC GEOLOGY. 


Feet. 
5. Coarse, friable, ash-colored sandstones of remarkably loose texture, 


matrix containing more or less calcareous matter, with sheets 
of pebbles, partly rounded and partly angular cherty masses, 
together with some fragments of Archzean schists, both horn- 
blendic and, granitoid: 2260 ae tes ee eee 150 to 200 


The Triassic beds are characteristically developed in North Park, 
especially on the western base of Medicine Bow Range from near the 
head of Retreat Creek south for sixteen or eighteen miles. The exposure 
from the base, where they rest unconformably against the Archean, up 
to the marls and limestones of the Jurassic, is nearly 1,000 feet. At the 
base are some light-colored sandstones, carrying pebbles, which are 
usually small, well rounded, and of a siliceous nature, the cement being 
extremely fine ferruginous sand, which breaks with a rough fracture, 
allowing the pebbles to drop out at a blow from the hammer. A similar 
exposure is seen on the western side of the Park, where again it rests 
unconformably upon the Archean. There is only one point in the Park, 
and that near the head of the eastern of the three forks of the Platte, 
where are interposed any Paleozoic beds between the Trias and the 
Archean. At that point, for a distance of not more than two miles, the 
conformable underlying Carboniferous limestones are interposed. From 
the thickness of the overlying Cretaceous which is exposed in this Park it 
is evident that the basin was very deep, and it is not at all improbable that 
it is underlaid throughout by the whole series of Paleozoic rocks which 
are displayed in Colorado Range. 

At Elk Mountain and Cherokee Butte the belt of conformable strata 
wrapped around the Archean mass contains the Trias, which here presents 
very generally the characteristics seen on the eastern base of Laramie 
Hills. The series is distinctly defined here by the Carboniferous limestones 
below and the soft, Jurassic shales above. At Cherokee Butte, a little to 
the south of the trail, the Trias is the uppermost member of the inclined 
series, and passes directly under the North Park Tertiaries which obscure 
the Jura. There are about 800 feet in all. 

The western slope of the Rawlings quaquaversal uplift is marked by 
concentric monoclinal ridges. The Trias here shows a thickness of about 


TRIASSIC. 259 


700 feet, and at the base is formed of pinkish sandstones of rather fine tex- 
ture and thinly bedded, the upper portion having more of a massive habit 
and being a deep Indian red. About half-way up in the series is a bed, 
only about a foot thick, of greenish-drab lithographic limestone, enclosed 
in soft clays of variable purple and red. This bed is of interest here, since 
it recurs with great persistence along the flanks of the Uinta Mountains. 
The base member of the series is here noticeable for extremely thin joint- 
ing-planes. 

Along the western base of Park Range the Cretaceous is usually the 
lowest rock exposed, overlapping the rest of the conformable series and 
coming directly in contact with the Archean; but east of Hantz Peak, 
in a shallow recess of the Archean, and in contact with it, is a limited 
outcrop of red sandstones which have been referred to the Trias, al- 
though without any positive evidence. Farther south, near the southern 
limit of the map, where Moore’s Fork enters the Quaternary valley which 
lies between the Archzean and the ridge of Dakota sandstone to the west, 
at the base of the Dakota, are seen the shales and marly limestones of the 
Jura, underlaid by a long, narrow outcrop of the upper beds of the Trias, 
which, however, affords no indication of the thickness or general character- 
istics of the series. 

Uma Rance.—The Trias outcrops of Uinta Range consist of the edge 
of the upturned series displayed at four or five points at the northern base 
of the range, and a much broader and more intricate and extensive expo- 
sure on the south side, particularly in the eastern half of the range in the 
region of complicated secondary folds connected with Yampa Plateau. 

As displayed upon the northern margin of the range, its most eastern de- 
velopment is shown in the region of Vermilion Creek. The section of Trias- 
sic beds here laid bare, begins at the top of the series of shales which we have 
referred to the Permo-Carboniferous, the base portion consisting of red con- 
glomerate-bearing sandstones which carry a seam of drab limestone. Above 
these is a body of red sandstones of several hundred feet; then beds of 
massive buff sandstone varying from 600 to 1,000 feet, and corresponding 
to the cross-bedded sandstones of Flaming Gorge. Above these are fine 
white and red sandstones, with some intercalations of clay and shaly mate- 


260 SYSTEMATIC GEOLOGY. 


rials, this member equalling about 100 feet, making a total thickness of 
Trias of about 2,000 feet. It will be seen that in passing westward from 
the region of North Park, the Trias has at this point doubled in thickness ; 
moreover, that the prevailing color is no longer a pure brick-red, but the 
upper half of the series is a massive light-buff sandstone. These rocks con- 
tinue north from Vermilion Creek Canon about two miles, and then pass 
beneath the horizontal series of the Vermilion Creek Tertiary. 

The Trias is masked along the northern slopes of the range, until, west of 
Red Creek and west of the mass of Archeean quartzites and schists, it again 
makes its appearance, faulted down into contact with the Archzan and with 
the Weber quartzite. Its outcrops from this point west to the cation of Burnt 
Fork are characterized by remarkable sinuosities, of which the most con- 
siderable is where Green River cuts its canon into the Uinta Mountains at 
Flaming Gorge. Here the Trias bends from its cast-and-west course to a 
northwest course, crossing Flaming Gorge, then turns almost a right angle 
into a southwest strike for about four miles, after which, at Kingfisher Creek, 
it resumes the normal strike of approximately east-and-west. In Flaming 
Gorge Ridge the strike varies from east 50° south to east 50° north. At 
this point, the Tertiaries having been eroded from the Mesozoic series, the 
upper limit of the Trias is well marked by the variegated marls of the Jura 
and beneath by thin shale-beds of the Permian, which are interposed 
between the base of the sandstone and the summit of the Carboniferous 
limestone series. As displayed on Flaming Gorge Ridge, the following 
members are observed, beginning at the top: 


Feet. 

1. Massive, cross-bedded, white and buff sandstone. -...-..-..-- 400 to 450 

2. Yellow clayey ‘sandstones. - 22 — <2 eer ce ee eee 50 

3. Massive’ yellow sandstones -< -20<- eee *... 400 to 450 
4. Red sandstones with white seams, on the whole rather 

thinly: bedded .2: 2 inc 2 = elem 2 eee er eee 300 to 350 

5. Red, heavy-banded sandstones --.-.- .-.----------=--- 400 to 450 

6. Greenish and greenish-purple clays.....-.-------------- 200 to 250 


West of Flaming Gorge the valley of Sheep Creek follows the soft 
shales of the Permo-Carboniferous, leaving on the north high escarped walls 


TRIASSIC. 261 


of the Trias. At Dead Man’s Springs the massive sandstones of this north- 
ern wall have a dip of 50° to the north, and they are further character- 
ized by extensive deposits of gypsum. West of Sheep Creek the Trias 
continues to a little west of the valley of Burnt Fork. In the region of 
Mount Corson, the overlying Eocene and Pliocene beds, rising high on | 
the slope of the Uinta foot-hills, overlap the Cretaceous and Jura, and 
come in contact with the Trias. Close to the wooded ridges, far up on 
Burnt Fork, the upper massive yellowish sandstones of the Trias, locally 
flecked with red stains of oxyd of iron, are seen conformably underlying 
the Jura. Here the lower Red-beds, although colored on the map, are 
obscured by débris. But they are seen underlying the buff sandstones a 
little farther to the east, at the eastern base of Mount Corson. Still farther 
west of Burnt Fork they come out from under the Tertiaries in the region 
of Lime Pass and extend westward for seven or eight miles, showing but 
imperfect exposures. 

On the western side of Junction Peak, Little Snake River has eroded 
a deep valley through the Tertiary strata, exposing the lower members of 
the Cretaceous, the shales of the Jura, and underneath them the sandstones 
of the Trias, which rest conformably upon the soft shales of the summit of 
the Palzozoic. Thus exposed, the beds strike north 45° west, and dip 
about 45° to the southwest. 

The eastern edges of Escalante and Yampa plateaus are margined by a 
broad band of Triassic sandstones, which south of the cafon of Yampa 
River rapidly shallows in dip and broadens in area of outcrop, occupying a 
large portion of the southern Yampa Plateau. In the remarkable strike 
from Kast Mountain to Fox Creek, the upper buff sandstones of the Trias 
form a conspicuous topographical feature. South of the river the prevail- 
ing color of the whole Triassic outcrop is of the usual red. 

On the summit of Yampa Plateau, directly south of the junction of 
Yampa and Green rivers, is a fragment of the Trias which formerly capped 
the whole plateau and which has been spared by erosion. To the west of 
Yampa Plateau, around the two anticlinals of Section Ridge and Split 
Mountain, the Trias winds in a sigmoid curve, bending to the east around 
Island Park and resuming its normal westward trend along the southern 


262 SYSTEMATIC GEOLOGY. 


slope of the main body of the Uinta, by Tirakav Plateau. In these won- 
derfully sharp, complex curves the Trias has developed an amount of 
flexibility, a power to conform to sharp local bends, which is one of the 
most surprising orographical features of the region. 

A fine exposure of Trias is that laid open on Geode Cain, one of 
the upper forks of Ashley Creek. The first prominent ridge overlying the 
steeply dipping Bellerophon limestones is formed of a body of coarse, mas- 
sively bedded, deep-red sandstone escarped toward the north, and having 
numerous intercalations of saline impregnations, of which common salt is 
the chief ingredient. 

To the east of Geode Canon, between the two forks of Ashley Creek, 
is an exposure of thirty feet of solid white gypsum enclosed in the Trias 
sandstones and overlaid by red and white clays. Subjected to analysis, 
the gypsum is found to contain 76.7 sulphate of lime, 21.5 water. As 
exposed upon the surface, it has the appearance of a massive statuary 
marble, varied by pinkish and yellow veins. The red sandstones are here 
capped by harder, compact, yellowish-gray sandstones, above which are 
pale pink sandstones 300 or 400 feet thick, and above these a gap of 100 
feet or more, representing some soft, easily eroded beds, whose outcrop 
is lost beneath the surface accumulations. The pinkish sandstones are 
capped by the beds of flaggy red sandstone, and above that is a line of 
cliffs composed of 200 feet of yellowish sandstone, above which appear 
the heavy white cross-bedded sandstones about 600 feet thick. The 
cross-bedding here develops a remarkable section, in which the flow- 
and-plunge action are found inclined 30° and 40° to the true planes of 
stratification. Here are altogether exposed about 2,000 to 2,500 feet of 
Triassic sandstones. Within the Uinta, gypsum has only been observed in 
this region, and on Sheep Creek, at the northern base of the range. The 
failure to observe the sulphates cannot be wondered at, when it is remem- 
bered how much of the Trias is obscured by débris, and that the shales 
which enclose the gypsum are, more than all other parts of the series, 
liable to rapid degradation. 

In the reéntrant synclinal between Split Mountain and the main ridge 


the Triassic beds range high around the eastward curve, almost to the sum- 


TRIASSIC. 263 


mit of Yampa Plateau, forming a line of curved bluffs with steep escarp- 
ments always toward the hills, while the backs of the dipping beds form 
approximately the outer surface of the slopes. 

At Obelisk Plateau is a portion of the massive cross-bedded sand- 
stone of the Upper Trias, dipping 29° to the southwest and striking north 
65° west. Near the mouth of Antero’s Canon, on the west branch of Ute 
Fork, the upper cross-bedded sandstones appear prominently on the eastern 
side of the gateway formed by the mouth of the canon, where are exposed 
about 1,500 feet of white and brownish sandstones standing at the angle 
of 70°, with the lower, red strata conformably below them. 

From Obelisk Plateau as far west as Heber Mountain on the meridian 
of 111° 5’, the nearly horizontal Uinta Tertiaries extend far up the flanks 
of the range, often overlapping the whole Mesozoic series and coming in 
contact with the Upper Coal Measures, but at intervals eroded away, open- 
ing more or less exposures of Mesozoic rocks. At the heads of Lake Fork, 
especially in the gateway of the western branch, are exposed about 1,500 
feet of Triassic sandstones dipping 380° to 35° south, and striking north 
65° to 75° east. Here the uppermost exposures are about 600 feet of 
light-colored, buff, cross-bedded strata, which are capped by shaly clays 
assumed to be the bottom of the Jura. Under the cross-bedded series are 
yellowish-white sandstones, gradually becoming redder with increase of 
depth. 

Still farther west, in the cafion of the east branch of the Du Chesne, the 
following members of the Trias are uncovered: The upper limit is well 
inarked by a limestone carrying Pentacrinus asteriscus, which is considered 
to be the base of the Jura. Beneath this appears the white, cross-bedded 
sandstone, 600 to 700 feet thick, underlaid by 200 feet of yellowish sand- 
stone; below that, 300 to 500 feet of pinkish-white sandstone, beneath 
which is the seam of greenish limestone, with some shaly sandstone. This 
greenish limestone is the one before mentioned, which occurs as far east as 
the Rawlings uplift, and in future study will doubtless be correlated with a 
similar limestone sheet observed along the flanks of Colorado Range. Be- 
neath the horizon of the limestones are 5V0 feet of deep, brick-red sandstone. 


Between the two bodies, and near the greenish limestone, was found a 


264 SYSTEMATIC GEOLOGY. 


Naticopsis, a new species, having somewhat of a Jurassic aspect. The 
total exposure here is about 1,900 feet. 

West of the Du Chesne Fork, along Stanton Creek, are afforded some 
excellent developments of the massive light buff sandstone, the upper mem- 
ber of the Trias. This exposure extends nearly to the head of Stanton 
Creek, the whole valley bottom being on the Triassic beds. West of the 
head of the creek they are masked by the overlying Tertiaries, which here 
rise to a great height, and further by the floods of trachyte which over- 
pour the region for many miles to the north. Below the trachytes at Heber 
City, however, the foot-hills are formed of broken outcrops of reddish sand- 
stones striking northwest and dipping at 25° to the southwest. They are 
undoubtedly the lower red sandstones of the Trias, and are here in the very 
position which might have been predicted by the known curvature of the 
underlying strata of the Uinta. North of Kamas Prairie, for many miles up 
the valley of the Upper Weber, heavy Triassic sandstones are seen dipping 
to the north. They are well exposed just north of the mouth of the cation, 
where it emerges from Uinta Range upon Kamas Prairie, and here consist 
of heavy reddish beds intercalated with some clays and bearing one or two 
minor sheets of pebbles. In passing upward they are much covered by 
dcbris, and to the west are masked by the overlying trachytes; but enough 
could be seen of the upper members to recognize the massive cross-bedded 
sandstone, which is here redder than to the east, although the distinctive 
structure is as clear as at any place. At Peoria, a little village just 
north of the remarkable right-angle made by Weber River at the northern 
margin of Kamas Prairie, the erosion of the trachytes along the river valley 
displays the Triassic strata on both sides, overlaid by variegated marls and 
shales of the Jura. The dip is usually 50° to 60° to the north. There 
are 700 or 800 feet exposed, the lower members appearing under the tra- 
chyte. The upper portion, instead of the pale buff or white color charac- 
teristic of the cross-bedded series east and south of the Uinta, is here 
of the same bright pinkish tint which is seen at the quarry farther down 
Weber River below Echo City. The upper members, however, display the 
intricate cross-bedding which is characteristic of this horizon. 

Wausatcu Range—In Parley’s Park the foot-hills which border the 


TRIASSIC. 265 


valley on the western side are made of the ordinary Triassic sandstone 
dipping to the east. <A little way below Kimball’s they make a sudden 
right-angle bend, and strike to the east and dip to the north. The trend 
of this chain of outcrops continues east-and-west until the ends of the 
strata are sharply cut off upon the line of the western foot-hills of the 
range. Here, between Parley’s and Emigration cafions, the prevalent north- 
ern dip is varied by a local anticlinal including a little Permian within its 
axis. Directly north the characteristic rocks reappear with their normal dip 
to the north, passing under the synclinal of Emigrant Canton and reap- 
pearing on the spur east of Camp Douglas with a southerly dip. The sand- 
stones as they outcrop on the margin of Salt Lake Valley are pinkish, 
rather loose-grained rocks, varied in their lower horizons by considerable 
clay. It is difficult to determine closely the thickness of the Trias here. It 
seems hardly to exceed 1,200 feet. The rock near Camp Douglas is more 
compact than south of Emigration Canon, and splits evenly along the 
planes of stratification, producing an excellent building-stone. 

An important outcrop of the Trias is seen in Weber Canon, just below 
the mouth of Lost Creek. Here, at a prominent bend of the river, and at the 
eastern end of the wonderful exposure of Paleozoic rocks described in the 
preceding chapter, overlying the 650 feet of Permo-Carboniferous shales, the 
Triassic series is exposed, about 1,000 feet in thickness, displaying the same 
general distinction of color seen over this whole country, namely, a division 
of darker clay-bearing red sandstones below, and a series of lighter, though 
here pinkish, cross-bedded sandstones above. The distinction of color, 
however, is far less than in the eastern part of the Uinta, where the sand- 
stones are more loosely coherent and impure. Here the rock is a thoroughly 
compact sandstone and an admirable building-stone, for which it is exten- 
sively quarried by the Union Pacific Railroad Company. When exposed 
in bridge piers to the action of flowing water, it maintains its coherence 
very well. It is peculiar here by reason of a great number of joint- 
ing-planes and the occurrence of a white gypseous coating of all the 
joints. Underneath the cross-bedded portion is a thick bed of finely strati- 
fied sandstone, the colors varying from Venetian red to cream-color and 
pure white. A specimen of the compact rock submitted to analysis gave 


266 SYSTEMATIO GEOLOGY. 


94 silica, alumina being the principal impurity, with scarcely a trace of 
lime. The average dip is from 70° to 75° eastward. So far as observed, 
all the Triassic outcrops found along the base of the Wahsatch and 
in the country to the east are conformable with the underlying Paleozoic 
series. 

Province or Western Nevapa.—It is important to note that in pass- 
ing westward of Wahsatch Range the Trias never reappears until the 
meridian of 117° 20’ is reached in western Nevada. It there recurs in im- 
mense volume, lying altogether west of the ranges which are made up of 
Paleozoic and Archean members. In the ranges formed of the Triassic 
series in this western Nevada province there are no Paleozoic rocks, the 
Trias resting directly on Archean granites and gneisses. The region has 
been subjected to severe crumpling, irregular local displacements, and faults 
of stupendous extent, and has been deluged with repeated outbursts of vol- 
canic rocks. Finally, the depressed surfaces of the Triassic folds have been 
subsequently overlaid by extensive lacustrine deposits of Tertiary and 
Quaternary ages. As a result, the eastern limit of the Triassic formation 
touches the western limit of the Paleozoic, but their mutual relations are 
too much obscured by voleanie and Quaternary masses to be placed beyond 
doubt. Other arguments which will afterward be brought forward induce 
the belief that the Palzeozoic and Mesozoic are strictly nonconformable and 
unrelated groups. The westernmost of the great Paleozoic folds which 
occupy Central and Eastern Nevada is an isolated mass of limestones and 
quartzites which form the higher portions of Battle Mountain and Sho- 
shone Range. That chain of Paleeozoic elevations continues in a line 
nearly due south, though slightly swerving to the west, until it comes into 
near connection with the Sierra Nevada south of Owen’s Lake. The Wah- 
satch limestone and Ogden quartzite are easily recognized in Inyo Range, 
and this general north-and-south line, already mentioned as the western 
boundary of the Palaeozoic exposures, is believed to have been the western 
shore of the Palaeozoic ocean. West of the Sierra Nevada thin lime- 
stones of the Upper Carboniferous recur in connection with Triassic and 
Jurassic rocks, and have been considered by Professor Whitney as con- 
formable with them. But from Battle Mountain westward to the west- 


TRIASSIC. 267 


ern slope of the Sierra Nevada, over 200 miles, there are no Paleozoic 
rocks whatever. 

This region is essentially made up of three geological elements : first, 
an underlying Archean body; secondly, the conformable Mesozoic series, 
consisting of Trias and Jura, but no Cretaceous; thirdly, and of most super- 
ficial importance, the Tertiaries, volcanics, and Quaternaries, which cover 
fully half of the area. The Trias and Jura were deposited, as numerous 
exposures clearly show, upon an Archean and granitic foundation which 
possessed a highly accidented topography. As a consequence, now that the 
Triassic and Jurassic series have been violently displaced and crumpled, 
erosion frequently lays bare the peaks and ridges of the original Archean 
bottom, showing them to have been summits of erosion of considerable sharp- 
ness, and but slightly differing topographically from modern mountain peaks. 
The relation existing between the Archean and the overlying Mesozoic is 
almost precisely similar to that described in the previous chapter between 
the Archzean and the Paleozoic. . 

The Triassic ridges north of the parallel of 40° 15’ have an approxi- 
mately meridionaltrend. Southof thatlatitude they swerve to a southwesterly 
trend, nearly at right-angles.to the Sierra Nevada, which is the greatest of all 
the American Trias-Juraranges and developsanorthwest-and-southeast trend. 

One of the most curious features of this western Trias and Jura prov- 
ince is the fact that the deepest developments are confined to the three 
ranges—Havallah, Pah-Ute, and West Humboldt—and that to the west 
the original granite topography must have risen, as the Jurassic slates over- 
lap the Trias and come directly in contact with the granite, while west of 
the meridian of 119° the granite forms the principal feature, and the Ju- 
rassic slates are reduced to a thin edge. The deeper part of the sea, therefore, 
in which the strata of this province were deposited was narrow from east to 
west, and was characterized by granitic islands from the Sierra Nevada east- 
ward to the meridian of 119°. Thence eastward it rapidly deepened toward 
the Paleozoic headlands of Battle Mountain and Shoshone Range, reaching 
a depth which permitted the deposition of 18,000 or 20,000 feet of strata 
in the region of Pah-Ute and West Humboldt ranges. The whole condi- 


tions of the Triassic strata, as developed in this province, are so different 


268 SYSTEMATIC GEOLOGY. 


from the rocks of corresponding age east of the Wahsatch Mountains that 
in this connection it seems better to begin at once with the most character- 
istic, in fact the typical, locality, rather than follow a geographical descrip- 
tion, beginning with the easternmost members. Accordingly, since West 
Humboldt Range offers the most extended and instructive displays, their 
occurrence there will be described, as furnishing a key to the sequence of 
the whole region. 

West Humsotpt Rance.—This range is a fragmentary portion of an 
anticlinal fold whose axis is north 30° east, or diagonal to the meridional 
trend of the main northern portion of the range. The anticlinal itself is 
faulted on the axis, the western half forming the main body of the range, 
while the eastern member is depressed at the north, so that its beds rapidly 
pass under the Quaternary valley formation, but rise to the south until at 
Buffalo Peak they occupy heights nearly corresponding with the westerly 
dipping member of the anticlinal farther north. The range is further dis- 
placed by a northwest-and-southeast fault, which severs it into two dis- 
tinct portions. The line of this fault is marked by a valley which extends 
southeasterly from near the mouth of Sacramento Canon. The western 
member of the anticlinal, which occupies the whole range north of the 
mouth of Buena Vista Canon, consists at the base of a great thick- 
ness of quartzitic and argillaceous beds, which in passing northward are 
gradually depressed beneath the Quaternary, but to the south rise to the 
summit of the range, and at the head of Buena Vista Canon are seen to 
abut nonconformably against the mass of Archean granite and schist, 
which is one of the mountain-tops of the Mesozoic sea-bottom. This 
series, in passing southward, is exposed more and more deeply, until in 
Indian Canon a very great thickness is shown, probably not less than 
4,000 or 6,000 feet. Sacramento Canon also displays a vast thickness of 
these rocks. Toward the north they are simply argillites and siliceous 
beds interposed with siliceous argillites, but on approaching Buena Vista 
Canon they are observed to become gradually metamorphosed until they 
finally pass into a porphyroid which in situ and in hand specimens remark- 
ably resembles an erupted felsite porphyry. In the heart of the range 


south of Buena Vista Canon are passages which show absolutely no strati- 


TRIASSIC. 269 


fication, and, but for the unmistakable transition into unaltered beds to 
the north, might well pass for erupted rocks. This whole series contains 
no distinct beds of limestone, and wherever analyzed is remarkably free 
from carbonate of lime. Its lower limit is nowhere seen, and, owing to 
the disappearance of the strata-planes under extreme metamorphism, 
there is no possible mode of arriving at its total thickness. The upper 
limit, however, is sharply marked by an abrupt transition from the schists 
into a body of dark, carbonaceous limestone. To this whole underly- 
ing group of schists and porphyroids we have given the title Koipato, 
from the Indian name of this range. The directly overlying limestone 
forms the base of a remarkable alternating series of limestones and quartz- 
itic beds, characterized by fossils of the St. Cassian Alpine Trias age. The 
entire group, which is conformable within itself, and also conformably 
overlies the Koipato, consists of the following members, counting from the 
bottom upward: 


Feet 

i, Ibe Ss Sob Sees coe See Se eee ee 1,500 
2. Slaty quartzite (capped with black slates, 250 feet)....---.-.--- 1,500 
3. iMeayyiermucinous limestones... _ . 2 =.= jock «<2 ie cee e =o nj0 se 2,000 
Aeurewthiniy bedded quartzite 2.242522 2 jc s2e- 2 ctw. 2 | 800 to 1,000 
5. Limestone (owing to peculiarities of structure, thickness somewhat 

18) KOVR 8) 5 0} KO) OY 0) A Reem Bee ae eel ee 1,000 
Gy THY CUTE WALI Blas SE Re ea ee eee ee 2,200 to 2,800 


To this whole body of 10,000 feet of strata we have applied the name 
of Star Peak group, from its characteristic development at that impor- 
tant mountain. Directly overlying the uppermost quartzite at the north- 
west point of West Humboldt Range is a body of limestone about 1,000 
feet thick, capped with fine argillaceous slates from 1,000 to 1,600 feet 
thick, the upper members being concealed beneath the Quaternary. ‘The 
lower part of this limestone contains fossils of distinct Jurassic species, 
and is only mentioned here to bring out the fact that the Trias and the 
Jura are perfectly conformable. The Trias throughout this region, there- 
fore, begins with the Koipato or lower member, which is supposed to corre- 
spond to the dark Red-beds forming the lower half of our Triassic series 


270 SYSTEMATIC GEOLOGY. 


east of Wahsatch Range. The Koipato group is devoid of fossils, with 
the exception of a few crushed and distorted remains of the genus Nautilus, 
which were found in the American District south of Sacramento Canon. 
On the other hand, the Star Peak group yields an abundance of character- 
istic Alpine Trias forms. It will be remembered that the Trias east of the 
Wahsatch is also stratigraphically divided into two prominent parts of 
nearly equal volume: the lower Red-beds, which contain little or no lime- 
stone, and but few isolated beds of gypsum, and the upper Red-beds, which 
are characterized by occasional limestone seams of no great volume, and 
frequent occurrences of gypsum. These two Triassic seas, separated by 
a wide area of continental land, differ from each other in a manner 
which renders correlation next to impossible. If there is any correlation 
between the beds of the two series, it would seem probable that the Koi- 
pato is the equivalent of the lower Red-beds of the eastern sea, and that 
the overlying Star Peak group may be the equivalent of the upper Red- 
beds, the two being characterized by intercalations of limestone. 

A glance at the map will show that the Koipato group occupies the 
whole body of the range in the region of Sacramento Canon and Spring 
Valley Pass, and that it trends diagonally across the range, occupying the 
anticlinal fold, with the Star Peak group dipping to the northwest and 
southeast upon either side of this central mass. Passing north, the upper 
members of the Koipato form the foot-hills from Buena Vista Canton 
north to Santa Clara Canon, the valley Quaternary hiding the lower mem- 
bers. The greatest development is in the high hills directly north of Sacra- 
mento Canon and Spring Valley Pass, but some of the most characteristic 
rocks are obtained from the head of Buena Vista, Cottonwood, and Indian 
canons. Near the northern end of the outcrop, at the mouth of Star 
Cajion, the upper members of the Koipato are shown, consisting of slaty 
quartzites, with an imperfect, irregular cleavage, in general of dark greenish 
grays and brown colors, with a slight calcareous admixture near the 
upper limit, while the lowest members are more purely argillaceous. 
The very summit strata form a little transition-group of fine red and yellow 
marls, immediately sueceeded above by the black basal limestones of the 
Star Peak group. Downward the marls become more arenaceous, and are 


TRIASSIC. AA 


followed by thickly bedded quartzites, more argillaceous below and more 
altered. Southward they pass gradually into the remarkable series of the 
Koipato porphyroids. In the region of Buena Vista and Cottonwood canons 
the upper marls are rapidly succeeded downward by argillites and clayey 
mud rocks, with alternations of coarse grits and excessively fine hornstone. 
Pale olive argillites of remarkably impalpable grain are seen along the 
northern ridge of Cottonwood Cation. The analysis of this bed is given in 
the Table of Stratified Rocks. 

On the same ridge are some interesting light-drab cherts, having a 
conchoidal fracture, and showing under the microscope a very microcrystal- 
line texture. For its chemical composition, see Analytical Table of Sedi- 
mentary Rocks. In general, the unmetamorphosed beds of the Koipato group 
are either purely siliceous or highly siliceous argillites, which are low in all 
chemical bases except alumina and potash. [rom these unaltered forms the 
transitions are very gradual, showing every change between the original con- 
dition and the purely suberystalline metamorphic porphyroid, in which limpid 
crystalline grains of quartz and imperfectly developed orthoclastic and tri- 
clinic feldspars are clearly visible. One of the most interesting of the transi- 
tional forms is the development of parallel white planes of crystalline feldspar, 
interlaminated with dark felsitic zones, which owe their deep colors to freely 
disseminated microscopical carbon. These earlier stages of metamorphism 
usually show all the feldspathic material in parallel planes. A rather more 
advanced stage shows distinct individualized crystals of feldspar, more or 
less perfectly bounded in a true microfelsitic groundmass, which some- 
times contains fully developed crystals of quartz or of feldspar, some- 
times of both. he felsitic groundmass shades all the way from black 
through purple, gray, green, and brown, at times showing shades of pale 
gray and drab nearly reaching pure white. Under the microscope the 
quartz grains are frequently seen to enclose foreign fragments resembling 
the groundmass. These inclusions, however, do not in their form or ar- 
rangement resemble the inclusions of igneous rocks, but are rather to be 
classed with the dust-like microlitic impurities observed in the feldspars of 
diorite. Minute flakes of white mica and grains of magnetic iron not infre- 
quently occur. The microscopical and chemical analyses unite to demon 


22 SYSTEMATIC GEOLOGY. 


strate the invariable presence of carbon, which sometimes reaches so high a 
proportion as to render the thin section entirely opaque. In the region of 
Cottonwood Canon the felsitic groundmass is more coarsely crystalline, 
and the feldspars more highly developed, many showing under the micro- 
scope the characteristic twin striation of the triclinic varieties. Local 
decompositions of this rock show cavities filled with ocherous substances, 
resulting from the decomposition of magnetic iron. Near the head of In- 
dian Canon, where the summit members of the Koipato group are reached, 
the metamorphism has extended upward into the horizon of the marly rocks 
which mark the summit of the group; and here the microscope shows a 
great deal of reddish calcite in the felsitic matter, the calcite containing a 
great deal of earthy oxyd of iron, besides some grains of quartz. Directly 
under these calciferous porphyroids are some brownish-gray rocks, in which 
the feldspar and quartz grains are very large and prominently developed. 
The analysis of the rock is given in the Table of Analyses of Sedimentary 
Rocks. 

Here, then, is a group of rocks of the lower Triassic horizon, which 
are traceable from their original condition as siliceous and argillaceous sed- 
iments, through all the stages of metamorphism, up to the development of a 
truly crystalline rock, and, as the analyses show, without the addition of any 
further chemical constituents, the ultimate composition of the porphyroids 
agreeing absolutely with those of the unaltered argillites. They are charac- 
terized by the almost total absence of soda, the low percentage of lime, the 
high and almost uniform percentage of potash, and the comparatively regu- 
lar ratios of silica and alumina. These rocks, it seems to me, possess an un- 
usual importance, from the fact of this rapid transition into the erystalline 
state without the admixture of other elements, without the interference of 
subterraneous heat, and without having suffered a change at any great 
depth. They were never overlaid by more than 14,000 or 15,000 feet of 
rock at the utmost, and it is evident from the inspection of almost any deep 
section that the weight of that amount of overlying material is insufficient to 
produce the molecular change observed here. Moreover, the metamorphism 
is very much localized. It is contiguous to an underlying granitic moun- 
tain, and it is also within the arch of an anticlinal which has been subse- 


TRIASSIC. 273 


quently subjected to very great compression and final fault. If my views 
concerning the origin of granite, as set forth in the Archean chapter, are to 
have any weight, the production here of the purely crystalline schists 
within the compressed region of an anticlinal fold would seem, without vio- 
lating the probabilities, to be due to local pressure alone. In treating of 
the interesting modification of the crystalline schists in Humboldt Range, 
(page 67), a series of changes was described by which the parallel gneiss- 
oid arrangement of the constituent minerals was broken up by longitudi- 
nal compression, and the granitoid result obtained. In this case there is 
the actual development of crystalline minerals—quartz, feldspar, and horn- 
blende—and of a cryptocrystalline felsitic base. It is uncertain whether the 
flakes of mica are the result of a new crystallization or were originally con- 
stituents of the sedimentary beds. While the weight of overlying masses, 
such as we know must have overtopped the Koipato beds here, could not 
by any possibility be supposed to induce the observed metamorphic change, 
the enormous compression to which the axial region of an anticlinal of 
20,000 or 30,000 feet of rock must have been subjected would probably 
afford the requisite pressure and mechanically disengaged heat for molec- 
ular rearrangement. In examining a series of rocks, from the loosest 
agglomerations of rounded sediments through the increasingly compact 
forms up to the purely crystalline state, the entire change may be expressed 
as a more and more intimate contact of the particles. It is not impossible 
that the granite mass which lay near this axis served as a fulcrum for the 
immense power of compression to work against, and this, perhaps, would 
account for the extreme forms of metamorphism in the immediate neighbor- 
hood of this granite mass. Granite having, if my views should be admitted, 
reached the limit of compression possible in the superficial crust, would offer 
a comparatively rigid body against which the beds of loosely compacted sedi- 
ment might be crowded and their volume diminished by the obliteration of 
those spaces which intervened between the original sedimentary particles. 

In Santa Clara, Star, Coyote, Buena Vista, and upper Cottonwood 
caiions the uppermost marls of the Koipato group are seen to be con- 
formably overlaid by limestone No. 1, or the basal member of the Star 
Peak Alpine Trias group. This zone is 1,200 to 1,600 feet thick, and near 

18 kK 


274 SYSTEMATIC GEOLOGY. 


the bottom is almost black, passing up into the ordinary grays and blues 
of a purer limestone. Between Star and Santa Clara camfions it is much 
fissured, and is stained red by infiltrated oxyd of iron. The carbonaceous 
matter which gives the black color to the rock is in varying proportion, but 
chiefly concentrated toward the bottom of the series. The analysis of a 
specimen of this rock is given in the table accompanying Chapter VI. 
Immediately above the Koipato summit marls the carbonaceous lime- 
stones are richly charged with Alpine Trias fossils, the faunal equivalents 
of the St. Cassian and Hallstadt beds of the Austrian Alps. They include — 


Halobia dubia, Gabb. 

Halobia sp.? 

Orthoceras Blakei, Gabb. 

Endiscoceras Gabbi, Meek. 

Trachyceras Whitneyi, Gabb. 

Trachyceras Judicarium, 

Trachyceras Judicarium subasperum, Meek. 
Gymnotoceras Blakei, Gabb. 

Arcestes perplana, Meek. 

Arcestes Nevadensis, Meek. 


From Buena Vista Canon were obtained — 


Modiomorpha ovata, Meek. 

Modiomorpha alata, Meek. 

Posidonomya stella, Gabb. 

Sphera Whitneyi, Meek. 

Arcestes perplana, Meek. 

Goniatites (Clydonites) levidorsatus, v. Hauer. 
Gymnotoceras Blakei, Gabb. 

Fragments of sauroid vertebrata. 


In Coyote Cafon but little search was made for organic remains. 
Nevertheless there were found, among poorly preserved forms — 


Ammonites Blakei, Gabb. 
Rhynchonella sp.? 


TRIASSIC. 275 


In Bloody Cafion, a small ravine between Coyote and Star cafons, 
were collected from the upper beds of limestone Ammonites sp.? 
Star Cation furnished — 


Ammonites Blakei, Gabb. 
Halobia dubia, Gabb. 
Arcestes perplana, Meek. 


Besides the above, there have been described from this limestone in 
Star Cafion, by Professor W. M. Gabb, the following forms : 


Spirvfera Homfrayji. 
Terebratula Humboldtensis. 
Ethynchonella lingulata. 
Posidonomya stella. 
Monotis subcircularis. 
Avicula Homfrayi. 


And from Buena Vista Cafion : 
Myacites (Panopea) Humboldtensis. 


The upper members of this limestone, not far below Star City, have 
yielded several saurian vertebrae. In general, the upper part of the lime- 
stone is more altered than the lower levels, and the fossils are correspond- 
ingly imperfect. The Halobia, although remarkably distinct in the lower 
part, in the upper are merely vague impressions. The rounder shells, like 
the Nautilus and Rhynchonella, although better resisting the prevalent alter- 
ation, are not infrequently replaced by erystalline calcite. 

Directly over limestone No. 1 is a body of slaty quartzite, varied by 
greenish chloritic schists and capped by 250 feet of black, carbonaceous, 
argillaceous slates. The entire thickness is about 1,600 feet. No fossils 
were obtained here. The prevailing character is not unlike the unaltered 
part of the Koipato group. Chemically, it closely resembles it. The 
upper members of the black slates become perceptibly calcareous, the 
microscope showing minute striated crystals. The green chloritic schists 
appear a prominent feature of this group, and are scattered at intervals 


276 SYSTEMATIC GEOLOGY. 


through the entire 1,500 feet, showing rudimentary feldspars. See analysis 
in table cited. 

The microscope shows the same prevalence of carbon, the same un- 
finished feldspar crystals, evidently developed in situ; and looking back 
the reader will see that the analysis is quite like those of the Koipato 
group. This member is therefore essentially the chemical equivalent of the 
Koipato, but in a far less altered condition. The dip of these schists is 
about 40° to the west. 

Directly above them, and quite conformable, is limestone No. 2 of the 
series, a very heavily bedded, gray, semicrystalline body, about 2,000 feet 
thick. This is much fissured and stained with oxyd of iron, and the few 
fossils which have been found are too indistinct for specific determination. 
They are known to belong to the genera Ammonites and Rhynchonella, 
however, and are most probably of the species more perfectly preserved in 
the lower limestone. A remarkable display of this limestone is made in the 
south fork of Star Canon, and at the head of the north branch of Coyote 
Canon. Here the abrupt slope of the prominent spur of Star Peak exposes 
a precipitous front of 800 or 900 feet, in which the beds of limestone, 
although rendered indistinct by crystallization, are seen in a general way 
to incline westward, quite conformable with the underlying quartzites and 
schists. 

The top of this great body of limestone passes by a rapid marly 
gradation into a pure white quartzite, intercalated with finer siliceous 
schists. The thickness of this body is not known, but it can hardly be over 
1,000 feet. It is essentially a true quartzitic member, and hence differs 
from the argillaceous strata of the Koipato and that which separates the 
limestones (No. 1 and No. 3). 

The immediate summit of Star Peak is made of a black, carbonaceous 
limestone, which directly overlies this quartzite, and in the series is desig- 
nated as limestone No. 3. While the trend of the range here is pretty 
accurately meridional, the strata all strike across the range at an angle of 
about north 30° east. In consequence, the members pass diagonally 
across the summit, and the quartzite which lies between the first two lime- 
stones is distinctly seen at the head of Buena Vista Canon, occupying a 


TRIASSIC, 26% 


position near the crest of the range. The quartzite which overlies lime- 
stone No. 3 probably crosses the top of the range at a point where it is so 
covered by soil and débris as to be unnoticeable. 

Limestone No. 5, whose lowest carbonaceous members form the sum- 
mit of Star Peak, slopes conformably to the west, and forms the surface of 
the mountain, extending some distance down toward Humboldt Valley. 
The varying dip and the accumulations of surface material make an esti- 
mate of its thickness difficult. It may be roughly set down at 1,000 feet. 
The dip of this limestone declines to about 18°. 

Over it, and especially well exposed in Humboldt Canon on the west- 
ern side of the range, is a heavy body of quartzite of a pure siliceous type, 
characterized by many interesting cross-jointings. The character of the 
exposures makes this member also hard to estimate, but we consider it to 
be over 2,000 feet thick. 

This closes the Alpine Trias group. It is immediately overlaid by a 
limestone containing different Jurassic types, which will be described in the 
Jurassic section. Here, therefore, the Alpine Trias consists of three lime- 
stones and three quartzites, the whole about 10,000 feet thick, making, 
together with the Koipato, a known thickness for the exposed Triassic 
series of about 15,000, or possibly 17,000 feet. As before noticed, the meta- 
morphic character of the deep exposures of the Koipato renders an estimate 
of their thickness impossible, but from all that we could see there could 
hardly be less than 4,000 to 6,000 feet. The exposures of Alpine Trias in 
the Star Peak group are probably exceeded in California, but their extreme 
metamorphism again in the great belt of upturned rocks in the Sierra 
Nevada renders the reconstruction of a section exceedingly difficult. 

The eastern half of the anticlinal of this range is a mere fragment, 
its eastern edge depressed beneath the Quaternary of the plain. The face 
corresponding to the axial fault is raised to a height nearly equal with 
that of Star Peak. The strata which dip eastward from 28° to 45°, and 
even 50°, are thoroughly conformable throughout, and display a partial 
repetition of the sequence already described at Star Canon. Along the 
western face of the hills west of Buffalo Peak, northward to Sacramento 
Canon, are found the porphyroids, less altered and rather more thinly 


278 SYSTEMATIC GEOLOGY. 


bedded and regular than farther north. These partly crystalline schists 
contain half obliterated remains of the genus Nautilus. Limestone No. 1 
of the Star Peak group occurs directly over these schists, and yields the 
following fossils : 

Halobia dubia, Gabb. 

Trachyceras W hitneyi, Gabb. 

Ceratites Haidingeri, Gabb. 

Ammonites sp.? 

Ammonites sp.? 

Goniatites levidorsatus, v. Hauer. 


The summit of Buffalo Peak consists of a heavy body of limestone, 
which is underlaid by a quartzite appearing to pass over limestone No. 1, 
described above as bearing fossils. This section of the range consists, 
therefore, of a small exposure of the upper part of the porphyroids of the 
Koipato, which contain fragments of Nautili, and limestones No. 1 and 
No. 3 of the Star Peak group, with their intermediate quartzite. 

West of the northwest fault before mentioned as separating the range 
into two parts, outcrops a heavy bed of limestone, which is similar in all 
respects to the lower and middle limestones of the Star Peak group, darkly 
carbonaceous at certain levels, and again passing up into a pale gray 
rock. The lower dark members contain indistinct forms of Ammonites 
and Rhynchonella. The rest of the range, to its termination in the Mopung 
Hills, shows more or less altered members of the Star Peak and Koipato 
groups, dislocated, displaced, and deluged with subsequent volcanic rocks. 
They yield no fossils, and throw no additional light upon the character- 
istics of the Trias of the region. 

Pan-Ute Ranee.—In its larger features, this ridge, next east of the 
West Humboldt, repeats the structure of that range in the same latitude. 
North of the great basaltic mass of Table Mountain, the range consists of a 
granite nucleus, which outcrops at Granite Mountain and north of Spauld- 
ing’s Pass, unconformably overlaid by an immense but obscure series of dark, 
varied siliceous and argillaceous schists, considered to correspond with the 
Koipato group of West Humboldt Range. The orographical structure, 


TRIASSIC. 279 


however, is far more complicated, and the relations of the beds are never 
made out with the same clearness as at Star Canon or Buffalo Peak. Di- 
rectly south of Granite Mountain, the Koipato group, which here forms 
the eastern member of the anticlinal, dips east, and is overlaid by the 
heavy basal limestone of the Star Peak group, the latter overlapping the 
Koipato quartzites as it passes north, and coming into unconformable con- 
tact with the Archzean of Granite Mountain. As the limestones are thrown 
westward and wrapped in a curve around the western base of the Archzean 
mass at Wright’s Cation, so here the easterly dipping Star Peak group 
limestone trends in a curve around the eastern base of the Granite Mount- 
ain Archean mass. 

The whole northern part of the range is subject to severe local disturb- 
ances and dislocation. The Star Peak limestones rise in a nearly vertical 
position, developing a sharp anticlinal, whose eastern member rapidly passes 
under the Quaternary of the plain, while the western or more important 
member dips at angles varying from 20° to 80°, and is thrown into a variety 
of contorted positions, besides being broken by numerous faults, which are 
traced with difficulty. As a result, the section does not approach in value 
that of Star Cafion. In the dark limestones south of Dun Glen—the low- 
est member of the westerly dipping series, correlated by us with the basal 
limestone of the Star Peak group—were obtained the following forms: 


Pentacrinites asteriscus, M. & H. 
Spiriferina Homfrayi, Gabb. 
Spirifera (Spiriferina) alia, n. sp. 
Terebratula Humboldtensis, Gabb. 
Edmondia Myrina, n. sp. 


From the same formation Professor Gabb has described the following 
species : 
Nautilus multicameratus. 
Ammonites Homfrayi. 
Mytilus Homfrayi. 
Myophoria alta. 
Ethynchonella equiplicata. 


280 SYSTEMATIC GEOLOGY. 


Pentacrinus asteriscus, ordinarily considered a Jurassic species, is here 
found embedded with unmistakable Alpine Trias fossils, but associated also 
with Spirifera alia, a Palzeozoic type. Messrs. Hall and Whitfield remark: 
“We know of no species of Spirifera or Spiriferina in rock of this age re- 
sembling the one under consideration, or with which it can be confounded. 
The substance of the shell, like all those from the same locality, is badly 
exfoliated, and has apparently undergone some change which has to some 
extent obliterated the natural features, so that we are not able to say defi- 
nitely if it be punctate or not, and consequently are in some doubt in regard 
to its generic relations.” 

Havatran Rance—Like the Pah-Ute, Havallah Range offers a very 
complex structural problem which would occupy a far greater space 
than I permit myself here. It consists of an elevated mass of Triassic 
rocks, exposing both the Koipato and Star Peak groups, resting, as in the 
case of the Pah-Ute and West Humboldt, unconformably upon Archean 
bodies, and broken through by intrusive rocks of post-Jurassic age, and, 
finally, in Tertiary time deluged at the northern and: southern extremities 
by outflows of rhyolite and basalt. Immediately north of Golconda Pass 
it will be seen that the range is a single ridge of the Alpine Trias group, 
which bifurcates, the rocks of one branch resting upon the Archean granites 
in the region of Summit Spring, the other continuing northward to near the 
valley of the Humboldt, where it is masked by rhyolites. As shown upon 
the general section in the Geological Atlas in the cut corresponding to Map 
V., eastern half, the range consists of a mass of generally easterly dipping 
Star Peak rocks, of intercalated limestones, slates, and quartzites, which 
have minor folds, locally creating western dips. The angles in this part 
of the range are always low, and the surface of the country is so covered 
with débris that the actual sequence cannot be made out with clearness. 
The western ridge widens rapidly, gradually assuming the form of a broad 
anticlinal, which is much obscured by local disturbances. In the heart of 
the range, at Signal Peak, is a vast display of quartzitic and argillaceous 
rocks, considered to be the equivalent of the Koipato group, overlaid con- 
formably by masses of limestone, quartzites, and slates, referred to the Star 
Peak group. For the detail of this structure, as well as that of Pah-Ute 


TRIASSIC. 281 


Range, the reader is referred to Volume II., Chapter V. For our present 
purposes, it is sufficient to say that in the westerly dipping slates of the foot- 
hills has been found a single Triassic form, Halobia dubia, characteristic of 
the lower Star Peak. 

The Triassic rocks of this range have a peculiar interest from their 
near approach to the Carboniferous of Battle Mountain. Thus far, in pli- 
cated and disturbed masses of this and Pah-Ute Range, no Carboniferous 
rocks have been discovered. It is possible that they may be found here- 
after, and their relations to the younger Trias determined. Buta glance 
at the eastern half of Map V. will show that there is nowhere a direct con- 
tact of the Carboniferous and Triassic series. The hypothetical relation of 
the two series is shown upon the general Atlas section-sheet in section cor- 
responding to Map V., eastern half. There the Carboniferous rocks, both 
quartzites and limestones, are seen dipping westward at an angle of from 
25° to 30°; and immediately west of the granite mass the Trias appears in a 
nearly horizontal position. 'The formations are too far apart to assert that 
this discrepancy of angle offers any true solution of their relation. For 
reasons hereafter to be brought forward, they are considered nonconform- 
able; but it must be confessed that this conclusion is not derived from any 
observed contact of the series. 

Fis Creek anp Aucusta Mounrains.—This chain of elevations con- 
sists of a continuous mass of eruptive rocks, from granite to basalt, em- 
bracing the older rocks—syenite, diabase, and felsitic porphyries—and 
containing also andesites, trachytes, rhyolites, and basalt. Accidental 
erosion has laid bare at two points along the western foot-hills limited 
outcrops of sedimentary rocks. That near the western base of Mount Moses, 
in Fish Creek Mountains, consists of a body of quartzites closely resembling 
those of the Koipato group. They rest unconformably upon the granite, 
and are overlaid by a tremendous flood of rhyolites. Farther south, at the 
western extremity of Shoshone Pass, near Shoshone Springs, is another 
limited exposure of limestones and argillites, the dark color of the sediment- 
ary rocks forming a conspicuous contrast with the pale shades of the sur- 
rounding and overlying rhyolites. These limestones are crumpled into a 
sharp anticlinal fold, having a north-and-south trend, the eastern member 


282 SYSTEMATIC GEOLOGY. 


standing almost vertical, the western series dipping off at an angle of 20° 
to 25°. There must be at least 1,000 feet of limestone exposed here, with 
interstratified arenaceous and clayey beds. The limestones are at times 
very dark on their weathered surfaces, coated with a peculiar crust of car- 
bonate of iron, and locally converted into nearly white crystalline calc- 
spar, having a peculiar concretionary habit. South of the springs are 
some greenish cherts, quite like those of the uppermost quartzite member 
of the Alpine Trias, West Humboldt, and allied also to the conglomerates 
to be presently described in the Desatoya Mountains. The main body of 
limestone is characterized by numerous fossils of Jurassic facies, which will 
be described under their proper head. The rocks underlying the Jurassic 
are considered to belong to the Trias, and to represent the uppermost mem- 
ber of the Star Peak group. 

Desatoya Mounraixs.—The conditions here resemble those of the Au- 
gusta. The entire mountain body is a vast series of rhyolite outbursts, 
piled one upon another, which have failed to overflow a high summit 
directly north of the New Pass Mines, where is exposed a body of Triassic 
rocks about six miles from north to south by four miles from east to west, 
occupying the central ridge of the mountains, and upon the eastern de- 
clivity passing under rhyolites, but constituting the whole western mount- 
ain slope quite down to the plains. The central mass rises about 4,000 
feet above the surrounding valley, and consists of a monoclinal body 
striking north 20° east and dipping 30° to 35° westward. The larger 
portion of the mass, and the whole summit of the mountains, are com- 
posed of a great underlying member, not less than 6,000 feet thick, of 
greenish and purple cherty conglomerates with red cement, capped with 
about 1,000 feet of quartzites and conglomerates having a peculiar yellow- 
ish, weathered surface, passing up into a bed of purple argillaceous roofing 
slate. This series is considered to represent the Koipato group, and it is 
interesting as displaying, though in a less degree, some of the forms of 
metamorphism already described in West Humboldt Range. Green por- 
phyroidal conglomerates are a prominent feature, bearing close lithological 
resemblance to some of the conglomerates found in American District 
south of Sacramento Canon, in West Humboldt Range—the rocks men- 
tioned as bearing distorted casts of Nautili. 


TRIASSIC. 283 


The Koipato group in the Desatoya Mountains, so far as observed, bears 
no fossils. Indeed, its metamorphosed condition renders the future finding 
of fossils very doubtful. As compared with the same group in West Hum- 
boldt Range, the predominance of conglomerates is the main distinguishing 
feature. ‘The zone of roofing-slates, also, which forms the uppermost mem- 
ber of the group, occupies the position of the summit marls which imme- 
diately underlie the basal limestone of the Star Peak group in West Hum- 
boldt Mountains. As exposed in Ammonite Canon, the roofing-slate summit 
of the Koipato is succeeded conformably by dark, compact, earthy lime- 
stone, often extremely carbonaceous, and not less than 1,500 feet thick. A 
band of yellow calcareous shales forms the lowest member of this group, 
which is immediately succeeded by dark-blue, finely laminated, calcareous 
shales rich in Triassic fossils, especially of the genus Ammonites. From this 
horizon were obtained — 


Halobia dubia. 

Pteria (Avicula) sp.? 

Pecten deformis (fragment). 
Myacites sp.? 

Orthoceras Blakei. 

Ceratites Haidingeri. 

Ammonites Billingsanus. 

Goniatites (Clyodomites) levidorsatus. 
Ammonites (Gymnotoceras) Blakei. 
Ammonites Ausseanus. 


From the upper limestone beds were obtained — 
Spiriferina Homfrayé 
Terebratula sp.? 
Chemnitzia sp.? 
From the limestones at the southern point of the range, near the head 
of South Cation, were obtained also the following forms : 
Halobia dubia. 


Halobia (Daonella) Lomelli. 
Modiolopsis (Modiomorpha ?) ovata. 


284 SYSTEMATIC GEOLOGY. 


Modiolopsis (Modiomorpha ?) lata. 
Lima (Clenoides) Gabbi. 
Ammonites (Gymnotoceras) Blakei. 
Acrochordiceras Hyatt. 
Entomoceras Laubei. 

Lima (Limatula) erecta. 


As in Havallah Range, the Triassic and Jurassic exposures of the 
Augusta and Desatoya Mountains are never seen either in actual contact or 
even in proximity with the Paleozoic rock. As at the north, they are 
separated by broad Quaternary valleys or massive eruptions of Tertiary 
voleanic rocks. It is a matter of regret that the precise relations of the two 
series, as far as our work goes, are indeterminate along this line. West 
of West Humboldt Range, in the Kamma and Truckee Mountains, are two 
unimportant outcrops, which, from their petrological characteristics, have 
been referred to the Trias. They are, however, of no systematic importance. 


SECTION II 


JURASSIC. 


Rocky Movunrains.—In the conformable series of upturned foot-hill 
rocks along the eastern base of Colorado Range, next above the group of 
gypsiferous red sands of the Trias, lies a thin body of clays, shales, marls, 
and cherty limestones, varying from 75 to 250 feet thick, capped by the 
always easily recognizable conglomerate which forms the base of the 
Dakota or lowest group of the Cretaceous series. Along these foot-hills 
the group has yielded no organic remains, and it is referred to the Juras- 
sie purely on lithological and stratigraphical grounds; but so great is 
the permanence of this narrow series between the Cretaceous conglomerate 
and the Trias Red-beds that there is not the slightest doubt in correlating it 
with beds of similar position and composition farther west, which carry 
an abundance of the distinctive Jurassic fossils.* The upper limit of this 
series is uniformly marked by the cessation of soft shaly and marly beds, 
and the sudden transition to Cretaceous conglomerates. The lower limit 
of the Jurassic series is more variable and less definite. In certain places 
the uppermost Red-bed of the Trias is directly followed by marly clays 
and shales similar to the fossiliferous Jurassic marls farther west. In such 
cases the line is drawn at the top of the red sandstone; but it should not 
be forgotten that the upper members of the Trias farther west are them- 
selves not infrequently clay, and that the Jurassic fossils occur separated 
from the main body of the Trias Red by the similar marly and clayey 
material. At best, the line between the Trias and the Jura on the eastern 
base of the mountains is only indefinite. The variability in thickness from 
75 to 250 feet, it would seem, may be due partly to the original thickness 


* Since the above was in type Prof. O.C. Marsh has announced the discovery of gigantic Jurassic 
reptiles at Morrison and Cafion City, and at other points in middle Wyoming, where they are associated 
with Belemnites densa and other characteristic Jurassic mollusca. A fuller note of these discoveries will 


be found in the section of recapitulation of Mesozoic. 
285 


286 SYSTEMATIC GEOLOGY. 


of the deposition, and in great measure to the variability in compression. 
As a whole, the colors of the series differ from the light creamy Cretaceous 
above and from the prevailing red of the foot-hill Triassic below. They are 
often pinkish, grayish, and yellow, with cloudings of reddish-purple and pur- 
plish-gray in the region of the calcareous beds. 

A section taken near Box Elder Creek, where the stream leaves the 
mountains, at the maximum thickness of the series, gives a total of from 225 to 
250 feet. At the base is a reddish-yellow, friable sandstone, followed by thin, 
gray, arenaceous marls. Above that, and fading gradually into it, is a grayish 
marl with reddish-brown bands of clay and thin layers of sand, followed by a 
rusty orange sandstone banded with light-yellow clay; above this a cherty 
yellowish and bluish limestone of varying thickness, passing, by a gradual 
increase of arenaceous material, into a yellowish sandstone; next a thin, 
white marl, only a few feet in thickness, shading into gray and streaked 
with clay at the top, the whole capped by a friable, yellowish sandstone. 
Owing to the softness and crumbling nature of a large portion of these 
beds, the actual thickness of each is difficult to determine, as they pass 
into one another by imperceptible gradations, and, with the exception of 
the limestones, show hardly any marked individualization. 

The series has its greatest thickness in the region of the Big Thompson. 
Northward, toward Lodge Pole Creek, it is difficult to trace, on account of 
obscuration by loose soil and the increased resemblance to the Trias. 
Seventy feet will probably cover the extreme thickness in this region. 
Farther north the Jurassic again increases to 150 and 180 feet, the most char- 
acteristic beds being reddish-yellow sandstones, shales, and marls. In the 
period of conformable deposition the recurring concentration of limy strata 
increased during the Jurassic, rendering the actual beds of limestone thicker 
and more defined than in the Trias, and imparting to nearly all the sand- 
stones a marly nature. There are two distinct types of Jurassic limestone; 
one hard, dense, and cherty, often of a very fine lithographic type, usually 
gray; the other less compact, exhibiting a greater variety of color and 
texture, and usually dolomitic. A specimen of the latter is given in the 
table of stratified rock analyses, Chapter VI. 

Finally, gypsum, so prominently included in the Red-beds of the Trias, 


JURASSIC. 287 


recurs at various horizons in the Jurassic, lacking continuity of stratifi- 
cation, and never reaching a thickness of more than two or three feet. It 
is natural that a body so soft and easily eroded as the Jurassic should be for 
the most part covered up with deposits of loose soil, and that in general 
it should be an obscure member of the whole series. As will be seen 
farther on, however, the main characteristics persist with the thickening to 
the west, where are ample organic remains. 

In the geological province east of Wahsatch Range, the rocks of Ju- 
rassic age are the invariable and conformable accompaniment of the Trias. 
Its outcrops are brought to light by the same series of upheavals and sub- 
sequent erosions which has exposed the underlying Trias. While the rocks 
of the latter group are essentially a series of sand-rocks, those of the Jura 
are characteristically shales and shaly limestones. Their greatest thick- 
ness is immediately along the base of the Wahsatch, where the series attains 
a breadth of 1,800 feet. Thence they gradually thin out eastward, reaching 
a minimum of seventy-five feet along the eastern base of Colorado Range. 
This diminution of thickness from the most western to the most eastern expo- 
sures coincides with the habit of the whole underlying series. The Jurassic 
occupies an intermediate position between the varyingly coarse siliceous 
sediments below and the wide-spread sheet of grits and conglomerates of 
the Dakota Cretaceous above it. Between these two easily recognizable 
horizons the Jurassic series, where exposed, may invariably be recognized, 
and even in the absence of fossils its stratigraphical boundaries are so 
exceedingly well defined that throughout the area of the Fortieth Parallel 
Exploration its limitations are quite as clearly fixed by the character of its 
material as by palzontological evidence. 

The light, cherty, Jurassic limestones are well displayed near Big 
Thompson Cation, where the series is seen overlying the calciferous Trias. 
The limestone bed is here about ten feet thick, enclosed between fine, light- 
yellow marls. In the Big Thompson region, the plane of division between 
Trias and Jura is especially obscure, on account of the expansion of the cal- 
ciferous marls, which pass downward by a series of sandy transitions into 
the upper horizon of the Trias. 

Near the mouth of Box Elder Creek, where it emerges from the moun- 


288 SYSTEMATIC GEOLOGY. 


tains, is a good exposure of the Jurassic series about 200 to 240 feet thick, 
the various members shading into one another so much as to render it diffi- 
cult to distinguish them. Beginning at the top, it is capped by a reddish- 
yellow, friable sandstone, passing downward into gray arenaceous mars, 
the lower gray marls being banded with purple and grayish stripes and 
clay layers; these are underlaid by rusty orange sandstone with layers of 
light-colored clay ; beneath this the cherty limestone passes down into yel- 
low calcareous sandstone, which is followed by white marls descending 
into gray marls with clay, the whole resting upon fine gray and grayish 
friable sandstone, which is immediately underlaid by the upper part of the 
Triassic Red-beds. 

This difficulty of separating the upper Trias and the Jura is again 
observed on the western side of Laramie Hills, near Red Buttes In the 
upper part of the Jura series the limestone has a flesh-red color and 
uniform texture, and contains fine, gritty grains of sand. The pure 
limestone material, subjected to analysis, is shown in the table of analyses 
cited. 

Jurassic rocks occur from the Red Buttes southwestward to Red Lake, 
usually showing but limited outcrops, and those confined chiefly to the 
calcareous portion of the series. Upon the summit of the high Triassic 
plateau southeast of Red Lake are exposures, about 200 feet thick, of 
Jurassic rocks, the summit members having been eroded off. Beginning at 
the top, the beds are as follows: a sandstone body 100 feet thick, white 
and friable at the top, reddish-brown, slightly intercalated with variegated, 
clays and marls in the middle, passing downward into cream-colored, marly 
sandstone; beneath this, 25 feet of bluish-gray, cherty limestone, followed 
by 75 feet of grayish-white sandstone, which rests upon the yellowish-red, 
cross-bedded sandstone of the top of the Trias. 

At the dome-like quaquaversal upheaval at the northern edge of Map 
I., near the 106th meridian, at Como, the easily recognized Dakota sand- 
stones and conglomerates overlie a series of Jurassic rocks, which are 
exposed from 175 to 200 feet in thickness. Passing downward from the 
base of the Dakota Cretaceous, the Jurassic consists of, first, gray clays 


and sandy marls, containing a great many gritty particles of angular sili- 
) S ys 8 


JURASSIC. 289 


ceous sand; secondly, creamy marls, with thin, sandy layers; thirdly, bluish- 
drab, cherty limestones; fourthly, fine, ash-colored marls, with thin beds, 
varying in thickness, of light-colored limestones ; fifthly, gray and orange- 
colored marls, with coarse sandy intercalations; sixthly, a reddish-yellow 
sandstone, which is immediately succeeded by brick-red compact sandstone 
of the Trias. In the marls, both above and below the limestone, which 
lies a little above the middle of the series, occur numerous Jurassic forms, 
among them the following : 


Pentacrinus asteriscus. 
Belemnites densus. 

Tancredia Warreniana. 
Trigonia quadrangularis, n. sp 


The yellow and cream-colored marls two miles east of Como also con- 
tain lamellibranchiate fossils, though imperfectly preserved. While or- 
ganic forms are so rare as never to have been observed by us along Colo- 
rado Range, the Belemnites and Pentacrinus in the Como marls are enormously 
abundant, their hard forms weathering out of soft enclosing marls and 
clays, and lying freely strewn upon the surface. 

The Jurassic beds of North Park are recognized by their lithological 
characters, which are very persistent, and their unmistakable position 
between the red Trias and the Dakota conglomerate. The cherty limestone, 
so characteristic of the middle portion of the Jurassic, is very persistent 
through North Park, and wherever the surface of the series is not too much 
covered by Quaternary detritus, the limestone outcrops form a slight, per- 
ceptible ridge. 

The dome-like uplift of Rawlings Peak exposes the Jurassic series, 
which is here seen to possess somewhat different characteristics from those 
already described. Directly under the Dakota Cretaceous conglomerates 
are found beds of limestone dipping conformably with the conglomerate 8° 
or 10° eastward. The surface is so cumbered with débris that the soft 
and marly parts of the Jura are nowhere exposed. Directly over the 
Triassic sandstone, however, are about 100 feet of soft, argillaceous beds, 


including some seams of arenaceous material. Coming to the surface 
19 k 


290 SYSTEMATIC GEOLOGY. 


through the soft detritus some distance above are two outcrops of lime- 
stone, a dark earthy bed ten feet thick, overlaid by fifteen feet of arena- 
ceous limestone, containing — 


Camptonectes bellistriata. 
Eumicrotis sp.? 

Astarte sp.? 

Belemnites sp.? 

Ostrea sp.? 


Above these fossiliferous limestones is a gap of 100 feet obscured by 
soil, though showing slight outcrops of sandy argillites. 

Uinta Rance.—Among the inclined beds upon either side of the great 
anticlinal of the Uinta, the Jurassic series holds its appropriate place, and 
differs from the outcrops to the east, already mentioned, in a consider- 
ably increased thickness and large proportional addition of calcareous 
material. It is, however, still characterized by the predominating pres- 
ence of clays and shales, whose habit of easy erosion gives to the gen- 
eral outcrop of the series the same débris-covered and obscure character 
which has been previously noticed. There are outcrops of considerable 
importance on the eastern edge of the O-wi-yu-kuts Plateau, extending in 
a northwest direction from the valley of Vermilion Creek. Here the cal- 
careous members which occur in the middle of the group and at its base are 
reduced almost toa minimum. In the region of Flaming Gorge, and thence 
westward to Mount Corson, the displays of Jurassic rocks are more impor- 
tant and more clearly seen The general section is a basal member of lime- 
stone more or less shaly, and often almost entirely replaced by sandy 
shales, reaching a maximum, so far as our observations go, of 200 feet. It 
was observed by Major Powell reaching 250 feet. Above this is a variable 
thickness of sandstones and sandy shales, never in our observations ex- 
ceeding 250 feet, succeeded upward by a body of limestone which has 
been noticed by us reaching 300 feet in thickness, and above that by 
a body of variegated clays intercalated with thin beds of sandstone and 
certain marly sheets These clays, besides the middle and basal lime- 
stones, have all been observed to carry well defined Jurassic types of 


JURASSIC. 291 


fossils. In the Flaming Gorge region, from the middle limestones, we have 


obtained — 
Camptonectes bellistriata. 


Gryphea calceola. 
Pentacrinus asteriscus. 
Lihynchonella gnathophora. 


From the basal limestones at Sheep Creek have been obtained — 


Camptonectes bellistriata. 
Myophoria lineata. 

Gryphea calceola. 

Pentacrinus asteriscus. 
Belemnites densa. 

Trigonia (two species). 

Ostrea sp.? 

Volsella. 

Neritella (like N. Nebrascensis). 
Chemnitzia. 


Here also is a bed of gypsum. 


Upon Black’s Fork the upper horizon of the Jura is very well defined by 
the basal conglomerate of the Dakota Cretaceous, and its base equally well 
marked by the summit of the upper cross-stratified member of the Triassic 
series. In the basin-like head of Burnt Fork the middle group of Jurassic 
limestones outcrops, having a strike of 15° south of east and dipping 45° to 
the north, capped by white sandstones belonging to the upper part of the 
Jura. South from Dead Man’s Springs, the first noticeable outcrops are 
peculiar metamorphosed sand-rocks, on a steep ridge overlooking the gorge 
of Sheep Creek. Underneath these, and probably representing the middle 
Jurassic limestone, are calcareous beds containing the following fossils : 


Camptonectes bellistriata. 
Myophoria lineata. 
Gryphea calceola. 
Pentacrinus asteriscus. 


292 SYSTEMATIC GEOLOGY. 


On the southern side of the Uinta, in the region of Ashley Creek, over- 
lying the white sandstone ridges of the upper Trias, are intervals of clayey 
valleys, representing the lower shales and limestone of the basal part of the 
Jurassic series. They are here largely covered with soil and débris, and 
the limestone nowhere makes a clear appearance. A low ridge is traced 
through this clayey interval, which is formed of a gypsum bed. It is about 
25 feet thick, and is quite massive and compact, only differing from the 
snowy-white gypsums in the neighboring Triassic rocks by a grayish- 
white color. On analysis it yields 75 per cent. of sulphate of lime and 21 
per cent. of water. Like the Trias gypsums, these bodies are not exposed 
for any great longitudinal extent, and are considered as lenticular deposits 
in the clays. A little south of and hence overlying this, in a ridge of glis- 
tening light sandstone, is a second series of gypsum deposits. The sand- 
stones are capped by about 50 feet of blue and drab limy shales and lime- 
stones, carrying the following well defined Jurassic fossils : 


Gryphea calceola. 
Eumicrotis curta. 
Belemnites densa. 


The thickness of the series here is very difficult to estimate, but it is 
probably greater than on the northern slope of the mountains, and cannot 
fall far short of 750 feet. A little farther east, beneath the Wyoming 
conglomerate at the top of Obelisk Plateau, are clays intercalated with 
sandy shales, and having at times a somewhat odlitic structure. They carry 
numerous Gryphee calceola. 

At the western end of Uinta Range, near the village of Peoria, the cross- 
bedded Triassic sandstones are seen to be directly overlaid by a body of 
lithographic limestone, which has a peculiar habit of breaking into lenticular 
fragments. It is frequently intercalated with yellowish, earthy marls. Both 
the sands and marls carry numerous Humicrotes curte. These marls and 
limestones are overlaid by a series of variegated shales and soft beds, all 
quite conformable, passing up into friable sandstones and mauve-colored 
shales, which in turn are overlaid by conglomerates of the Dakota sand- 
stone, here exceedingly coarse. The middle of the Jura is somewhat 


JURASSIC. 293 


calcareous, but real limestone is mainly confined to the basal member, which 
rests conformably upon the top of the Trias. 

WausatcH Rance —At the head of the lower Weber Canon the upper 
cross-bedded sandstones. of the Trias are overlaid by a considerable body of 
yellow and blue limestone and calcareous shales, yielding — 


Cucullea Haguet 
Myophoria lineata. 
Myophoria sp. % 
Myascites subcompressa. 
Volsella scalpra. 


The lowest member of this basal limestone series is broadly and heavily 
bedded, but it passes upward into calcareous shales, which are interstratified 
with true lime-beds, the whole covering a thickness of about 600 feet. 
Above this is a long interval of soil-covered hill, through which the thin 
edges of shaly outcrops, both siliceous and argillaceous, are seen, growing 
more calcareous in passing upward, and at length covered by thin argilla- 
ceous shales carrying well defined ripple-marks. The whole Jurassic here 
is from 1,600 to 1,800 feet thick, and is prevailingly calcareous through the 
lower half and prevailingly argillaceous through the upper half, all its ma- 
terials being of a very fine grain. The strike here is 16° or 18° east of 
north, and the dip from 78° to 80° east. It is quite conformable with the 
underlying Trias and Paleozoic series, and forms the uppermost exposed 
member of the great conformable group. The latest argillaceous members 
of the Jura series here have yielded no fossils. A little southward, in Kast 
Creek Carion, at Parley’s Park, the plane of demarkation between the 
Dakota conglomerate and the Jura presents a distinctly characterized 
change, and the upper Jurassic rocks are thinly bedded argillaceous shales, 
quite similar to those which overlie the Devil’s Slide in Weber Cajfion, 
opposite the mouth of Lost Creek. 

Plate XII. is a view of the Devil’s Slide, an interesting projection of the 
harder sandy beds of the Jurassic above the surface, from whose flanks the 
softer shales have been eroded away. 


Western Nevapa.—Over the Mesozoic region of western Nevada, 


294 SYSTEMATIC GEOLOGY. 


~ 


within the Fortieth Parallel, and in the total absence of Cretaceous, the 
Jurassic is the uppermost member of the conformable group, and has hence 
suffered more from erosion than either part of the Triassic. In consequence 
only a small part of the Mesozoic exposure is of Jurassic beds. Character- 
istic fossils were collected by us at three points, and the range of the group 
was extended on competent stratigraphical evidence. 

I have shown that the uppermost of the three limestone bodies of the 
Star Peak Alpine Trias group is overlaid by a quartzite, and that in turn 
capped conformably by a heavy, gray, subcrystalline limestone. This is 
seen on the northwest point of West Humboldt Range and south of 
Buena Vista Canon on the east base. In these two positions the contrary 
dip and relation to the underlying Star Peak group show the upper lime- 
stone to be a high member of the great faulted anticlinal of the range. 

In the dark-gray beds of the east base are found Belemnites Nevadensis, 
a new species, and several indistinct, badly preserved bivalves. From the 
upper limestone of the northwest part of the range were collected Montli- 
valtea and Cardium too decomposed and imperfect for specific determination. 

A similar body of limestone about 1,200 feet thick has been exposed 
at the east base of the Augusta Mountains, nearly surrounded by great 
massive eruptions of volcanics; it is a mere isolated outcrop; all its oro- 
graphical connections concealed by the lavas ; even its stratigraphical base 
and summit lost; a mere fragment of limestone, but carrying in its upper 
members the following curious group of Mollusca: 

Terebratala Augusta, n. sp. 

Leptocardia carditoidea, n. sp. 

Leptocardia typica, n. sp. 

Aviculopecten (Eumicrotis?) Augustensis, n. sp. 
Pecten sp.? 

Pecten sp.? 

Gryphea sp.4 

Descina sp.? 

Meek, Hall, and Whitfield call attention to the extremely late facies of 
this collection, which, according to their judgment, has a Cretaceous and 


even an Eocene look. But the occurrence of Jurassic forms, which these 


JURASSIC. 295 


undoubtedly are, having the facies of a later fauna, is distinctly paralleled 
by the extremely late aspect of the Cretaceous fauna of California, whose 
upper members will in future, in my belief, be correlated with our Laramie 
group. 

Over the Jurassic limestone on the northern point of West Hum- 
boldt Range lies a very heavy body of variable but generally argillaceous 
slates. 

The exposure on Humboldt Cafion is of over 2,000 feet. And on the 
north side of the Humboldt valley the same slate group is exposed with 
even greater thicknesses. 

In the southwest extension of West Humboldt Range south of 
Oreana there is a very great thickness of the slates, which are there inter- 
esting from the great volume of extremely fine-grained papery shales 
intercalated in the other more slaty argillites. Under the microscope the 
Oreana shales and the slates from over the limestone at Humboldt Canon 
are seen to be thickly crowded with pale microlites, probably of feldspar, 
which have a close external resemblance to colorless microlites in the De- 
vonian slates of Germany. When looked at by reflected light through the 
loupe, all these microlitie slates show a peculiar fine play of light, evidently 
the effect of minute reflections from the microlitic facets. 

The Jurassic limestones do not recur in our part of Nevada west of 
West Humboldt Range, but the slates form a persistent sheet, which is 
seen in nearly every range lying directly on the Archzean rocks or abutting 
against the slopes of the old schist ranges. 

It is quite clear that these upper Jurassic slates are to be correlated 
with the similar rocks at Mariposa, in California, which are well charged with 
true Jurassic fossils, and are further interesting as being the containing 
rock of the great auriferous quartz lodes, as Prof. J. D. Whitney has shown. 

In the Nevada province, then, the Jurassic consists of a limestone 
between 1,500 and 2,000 feet thick and overlying slates probably about 
4,000 feet thick. 


SiC LLON. rite 
CRETACEOUS. 


At the close of the present chapter will be found an analytical map 
showing the distribution of pre-Mesozoic and Mesozoic exposures. ° The 
object of showing the superficial areas of pre-Mesozoic rocks is the same 
that induced me to show the Archzean masses upon the Paleozoic analytical 
map, namely, that the relation of the rocks of the period discussed, with 
the preéxistent masses may be clearly seen. A glance at this map will 
show where the Cretaceous rocks come in contact with older formations, and 
where they form the earliest masses of an outcrop. 

The chief fact of interest connected with the whole Cretaceous develop- 
ment is, that it does not continue west of the meridian of the Wahsatch. 
Kast of that line its exposure is simply a question of suflicient stratigraphi- 
cal disturbance to bring it to the surface, or the accidents of erosion 
which have removed it from its former high position. With the excep- 
tion of a small Archean region in the Rocky Mountains, altogether east of 
the 107th meridian, the whole region now occupied by the basin of Green 
River and the Uinta was evenly covered with Cretaceous sediments which 
are altogether marine, and are of interest as being the last oceanic strata 
covering the region between the 105th and 112th meridians in these lati- 
tudes. 

The Cretaceous here represented a period of comparatively uniform 
calm, so far as orographic disturbances go; and although it is characterized 
by successive subsidences, they were so general and gradual as to leave no 
traces of their mode of operation, except the succession of conglomerate 
strata and tiers of coal-beds. 

The Cretaceous formation is defined below by the occurrence of the 
Jurassic series, well identified through a considerable portion of its exten- 
sion by characteristic fossils. Between the Cretaceous and the Jurassic 
there is absolute conformity, except upon the immediate flanks of the 


Wahsatch, where the evidence is decidedly obscure and quite contra- 


296 


CRETACEOUS. 297 


dictory, the majority of the appearances indicating the usual conformity 
between the Cretaceous and the Jura; others, which it must be con- 
fessed offer a poor quality of evidence, point to a nonconformity here 
between the Cretaceous and the Jura, such as is observed on the western 
flanks of the Sierra Nevada in California, which formerly led me to believe 
that the Wahsatch and the Sierra represented the two shore lines of a Ju- 
rassic continent against which the Cretaceous rested unconformably. But 
I am now obliged to modify that view, and to believe that the Cretaceous, 
Jura, Trias, and Permian of the Wahsatch are all conformable. However 
that may be, from the Wahsatch eastward the entire Cretaceous series cer- 
tainly rests with absolute conformity upon the Jura. 

Immediately succeeding the close of the Cretaceous deposition a most 
powerful orographical movement took place, resulting in the plication of the 
Cretaceous and underlying rocks, the relative lifting of the Rocky Moun- 
tain region as regards the basin of Green River, and the draining of the 
Mississippi or mediterranean ocean. 

Within the area examined by us the rocks subsequent to the Mesozoic 
are altogether nonconformable with the Cretaceous, with the slight excep- 
tion of a region in the middle of the Green River Basin, where the lowest 
of the Eocene rests upon the somewhat eroded top of the Upper Cretaceous 
with coincidence of angle. Elsewhere there is a discrepancy between the 
Cretaceous and the Kocene, the lower part of the Kocene itself being made 
in great measure from the disintegration of the Cretaceous. 

There is no evidence whatever of the Cretaceous ever having passed west 
of the Wahsatch, and all the known facts contribute to support the belief 
that a region a little west of the Wahsatch, now faulted downward, marked 
the western limits of the Cretaceous sea. To the east it extended beyond 
the limits of the present Rocky Mountain system, and its deposits form a 
prominent feature of the geology of the plains eastward into Kansas. 

The upheaved sedimentary rocks along the eastern foot-hills of Colo- 
rado Range offer several admirable sections from the base of the Cretaceous 
far up into the series, and these exposures have formed the subject of con- 
tinued study by Dr. F. V. Hayden and the late Prof. B. F. Meek. The see- 
tion, as elaborated by them, has been constantly re-observed by us with 


298 SYSTEMATIC GEOLOGY. 


such concurrence of result that we have cheerfully adopted their nomen- 
clature from the base of the series up to the summit as defined by them. 
Beyond that horizon, and conformably overlying the Fox Hill group of 
Hayden, is a considerable series of rocks over which a conflict of opinion 
now exists. These rocks Dr. Hayden has successively considered as Ter- 
tiary and as transitional between the Cretaceous and the Tertiary. They 
conformably overlie the Fox Hill of Meek and Hayden, and are developed 
throughout a large part of Wyoming, as well as upon the great plains 
east of the Rocky Mountains south of the 41st parallel. That there 
might be no misunderstanding as to the stratigraphical position and nature 
of the rocks themselves, Dr. Hayden and I mutually agreed to know them 
hereafter as the Laramie group, and to leave their age for the present as 
debatable ground, each referring them to the horizon which the evidence 
seemed to him to warrant. It is proper that I should say here that the 
result of our investigations leads me to the distinct belief of their Cretaceous 
age, and in this examination of the stratigraphical geology of the Fortieth 
Parallel they are assumed to be within the upper line of the Cretaceous. 
Excepting this point of difference, we unhesitatingly follow the stratigraph- 
ical division of the Cretaceous already instituted by Meek and Hayden. 
Over the great extent of exposures upon which these rocks have been 
observed from Missouri to New Mexico, it is not at all remarkable that 
certain of the minor groups should be found to vary stratigraphically, while 
others remain uniformly persistent. Dr. Hayden himself mentions the fact 
that the Fort Benton, Niobrara, and Fort Pierre—his Cretaceous Nos. 2, 
3, and 4—were decidedly variable, and in some sections one or other of 
the members was entirely wanting, or its place was represented by a new 
petrological member. This experience of Dr. Hayden’s was repeated by 
us, and I appealed to him to offer a name which would represent the three 
groups combined. Accepting his suggestion of the name of Colorado, we 
have applied it to our maps and sections; and, as the legend at the side 
of the map will show, it is intended to embrace the three divisions. I now 
proceed to the examination of the Cretaceous exposures. 

Daxora Group.—Overlying the softer marls and shales of the Jurassic 


along the whole chain of foot-hill outcrops of Colorado Range, wherever 


CRETACEOUS. 299 


the whole inclined series is not overlaid by Niobrara Pliocene, the base of 
the Cretaceous is seen in the Dakota sandstones and conglomerates, a body 
varying from 200 to 300 feet thick, a strongly coherent rock, which resists 
weathering; and since it is overlaid by the softer materials of the Colorado 
group, as well as underlaid by the equally soft Jurassic, it forms a promi- 
nent outcrop, and throughout a considerable portion of many miles of expo- 
sure along the eastern base of the mountains from north to south, it ap- 
pears in wave-ridges with a sharp face toward the range, and the more 
gentle inclination of the backs of the strata toward the east. These ridges, 
which resemble the form of an in-rolling wave, have received the senseless 
name of “ Hog-Backs.” The base of the Dakota is usually a peculiar 
conglomerate, which passes upward into hard, yellowish-brown, rusty sand- 
stone, containing un irregular dispersion of iron oxyds. 

The basal conglomerate is a singularly persistent feature wherever we 
have found the lower Dakota exposed. Along the base of the Rocky 
Mountains it consists of a paste of gritty, fine, siliceous sand, containing 
small pebbles, subangular and rounded, of black, white, red, and brown 
cherts, with a few fragments of Archean schist which contain the crys- 
talline ingredients of a hornblendic gneiss, and a few pebbles of a mixture 
of red orthoclase and milky-white quartz, such as occur in the Archiean 
rocks of the Laramie Hills. An interesting feature of this conglomerate is 
the extreme induration of the cement. Under the hammer the conglom- 
erate breaks with almost equal difficulty through the matrix and pebbles. 
But the looser texture of the paste is detected in the constant weathering 
out of pebbles. Where exposed to drifting sands, the cement and pebbles 
wear down almost evenly. The difference in weathering is due not so much 
to difference of hardness as to difference of porosity between the pebbles 
and the cement. These conglomerates are variable in thickness, and pass 
up into hard, yellowish-brown sandstone, with distinct heavy bedding. 

The uppermost member is an exceedingly friable, nearly white sand- 
stone, characterized in some places by large amounts of carbonaceous mate- 
rial, and in others by a great deal of clayey iron ore. Along the northern 
part of Colorado Range, by Laramie Hills, the Dakota is often considera- 
bly shaly, while to the south it is more coherent and weathers in blocks 


300 SYSTEMATIC GEOLOGY. 


of considerable size. Analysis proves it to be very free from calcareous 
material. The microscope shows it to be made up predominantly of frag- 
ments of quartz, but to contain a good deal of fine argillaceous matter, and 
not a little of a chloritie earthy mineral. Its exact chemical constitution 
will be found in the table of analyses of stratified rocks. 

The Dakota sandstones occur very prominently in the mouth of Big 
Thompson Creek, where they form a powerful ridge 300 feet thick, which 
is their greatest development east of the mountains. The basal conglomer- 
ate is here seen to be overlaid by sandy, saccharoidal beds, followed by a 
white, almost quartzitic zone resembling the matrix of the conglomerate. 
The section is as follows: 


Feet. 

1. Coarse yellow quartzitic sandstones, frequently conglomeratic, pass- 
ing up into a yellowish-brown sandstone, almost a quartzite... 200 

2. Coarse yellow sandy beds, with frequent clay-seams, capped by a 
coarse, suvary sandstone 202 2 2o cee ae oc oe ee ee eee 100 
Potalhzs itor: dhe Age Jats PRES ee eee eee 300 


On the western side of the Archzean spur, directly north from Big 
Thompson, they dip 45° westward, with a general trend of north 35° or 
40° west. On the eastern side of the same Archzean body they resume 
their gentle eastern dip of 14° to 16°. 

Between the Cache la Poudre and Park Station is an admirable display 
of this formation in a strong outcrop with a north-and-south strike, dipping 
to the east at angles varying from 15° to 20°. Indeed, from the Big 
Thompson to the 41st parallel the Dakota forms an almost continuous ridge. 
It is again traceable from Wallbach Spring to Shelter Bluffs, and around 
the peculiar southwardly projecting promontory of Archzean at the Chug- 
water forms a marked horseshoe ridge rising above the low, valley-like 
outcrop of the soft, underlying Jurassic. 

On the west flank of Colorado Range, partaking of the gentle westerly 
dip of the stratified series which margin the western base of Laramie Hills, 
the Dakota group forms a wide belt, extending from the northern limits of 
our map ina due south line as far as Red Butte Station, when, following 


the curve of the conformably underlying rocks, it deviates to the south- 


CRETACEOUS. 301 


west until it abuts against Sheep Mountain. It thus forms a broad band 
from three to four miles in width, at the southern part lying nearly hori- 
zontal, and having an inclination of only 3° to 5° at the northern limit of 
the map So gentle is the slope, and so thoroughly covered is the 
surface of the plain with Quaternary accumulations, that outcrops are very 
rare. Here and there over the Jura shales are seen the harder conglom- 
erates, passing up into rusty coarse sandstones. On the whole the majority 
of outcrops are formed of a yellowish-brown sandstone, the upper mem- 
bers characterized by scattered occurrences of carbonaceous clays. 

South of the railway the inclination of the beds to the northwest is only 
from 1° to 3°. It is difficult in this nearly horizontal region to obtain the 
thickness accurately. Like all the gently dipping sedimentary rocks upon 
the western side of the range, this member seems to be thicker than in the 
corresponding positions on the eastern side, where the steeper easterly dips 
have been accompanied by much greater compression. 

At the little quaquaversal uplift near Como Station, the northern face of 
the ridge south of Como is formed of a reddish sandstone bearing Jurassic 
fossils, and immediately over this is the Dakota sandstone, here a compact, 
yellowish-brown rock, which readily breaks into huge cuboidal blocks, as 
observed in North Park and at various points along the wave-ridges of 
the eastern foot-hills. North of the lake a low wall of Dakota sandstones 
is seen dipping northeast at an angle of 35° or 40°. 

Along the eastern side of North Park the Dakota presents features very 
similar to those already described on the eastern side of the range. It over- 
lies the soft, marly shales of the Jurassic, which, as usual, are eroded out, 
forming a shallow valley to the east and underneath the Dakota. The 
latter, with a dip of 19° southwest, forms a bold ridge, which is continuous 
in front of the Archeean spurs, and is cut down by the streams that cross its 
trend. Asa whole the strike is due northwest, but is subject to a remark- 
able sinuosity, which produces short, broken ridges, and not the long, 
smooth, continuous wave-lines seen elsewhere. The exposure here, as shown 
on Retreat Oreck, is about 350 to 380 feet in thickness, and is composed of 
the usual yellowish-brown sandstones, not infrequently compacted into a 
quartzitic condition, together with the characteristic basal conglomerate, 


302 SYSTEMATIC GEOLOGY. 


the pebbles of which here were usually about the size of a filbert, and con- 
spicuous among them were fragments of pure white quartz and jetty-black 
chert. 

On the western side of the Park it comes directly in contact with the 
Archean along the eastern slopes of the great mass of Ethel Peak. It out- 
crops at intervals through an immense amount of glacial débris, dipping to 
the east at angles from 25° to 50°. Here, as at Retreat Creek, the black 
shales of the lower member of the Colorado are clearly seen in contact 
with the yellow sandstones. The thickness of beds here seems to have 
increased considerably over those displayed on the eastern side of the 
range. ‘There can hardly be less than 400 feet. 

One of the most interesting features of the geology of the whole Rocky 
Mountain region is the manner in which the sedimentary beds describe free 
continuous curves around promontories of Archean. At Elk Mountain, a 
circular, nearly isolated mass of Archean schists and granites, this phenom- 
enon is well shown. Overlying the Jurassic marls, which, as usual, form a 
region of comparative depression, the Dakota rises in the characteristic 
sharp wall which is cut through by only two or three creeks. At its north- 
ern base are seen the overlying Colorado clays in distinct conformity. The 
dip-angles here rise to 85°, with a strike of remarkably bold horseshoe curva- 
ture, as may be seen from the geological map. 

In a similar manner, around the entire quaquaversal uplift of Rawlings, 
above the earthy slope formed by the Jurassic marls, is seen the outcrop of 
powerful Dakota sandstones. An excellent exposure is that about four 
miles east of Rawlings Springs, where the characteristic basal conglomerate 
is seen to be made up of the usual dense cement, with pebbles the size of 
a filbert, of black chert and reddish-brown jaspers. The matrix, as devel- 
oped here, is seen under the microscope to be largely made up of the 
fractured and partially rounded fragments of crystalline quartz. Large 
blocks which result from the disintegration and degradation of the Dakota 
again display the fact that the matrix is as unyielding as the jasper pebbles. 
The western faces of bowlders, swept by the prevalent west wind, which 
often blows with great violence and is freighted with sharp, cutting sands, 
display excellent examples of wind-polish. The surface is as brilliant as 


CRETACEOUS. 303 


glass, and is modified by peculiar irregular protuberances and drill-holes, 
which cut through pebbles and matrix indifferently. The Dakota sand. 
stones here show a large amount of limpid quartz-grains and partially kao- 
linized orthoclase crystals. 

The heads of Yampa River, Elk River, and Moore’s Fork converge 
from a remarkable recurve in the Archean mass of Park Range. South 
of the great curve of Moore’s Fork the lowest of the younger series is the 
Trias, but north of Yampa Springs the Dakota sandstones overlap the Ju- 
rassic, coming into contact with the Archwan, as they do directly across the 
range at the base of Ethel Peak. 

In Uinta Range, above the canon of Vermilion Creek, is a broad, open 
valley, carved out of Cretaceous strata. The heavy masses of Triassic 
sandstones are overlaid by the usual variegated shales and marls of the 
Jura, which are here much eroded away. The quartzitic conglomerate 
appears at the base of the Dakota series, containing the well known black 
and white chert pebbles, which are unusually small. Besides the ordinary 
rusty-yellow sandstone, the group here encloses nearly 100 feet of yellow 
and grayish sandstones containing clay-seams. The total thickness is about 
500 feet. 

South of the Uinta, at Ashley Creek, the ridge of Jurassic limestone is 
followed by a deeply eroded trough which the overlying soil shows to be 
made up of red and purple Jurassic shaly clays. Immediately above this 
comes the pebble-bearing conglomerate at the base of the Dakota, which 
passes upward into a white sandstone. Over it are 150 feet of blue clay 
slates, again overlaid by compact brown sandstones, which form the summit 
of the Dakota and which here carry Inoceramus Ellioti, Cardium n. sp., and 
Lucina or Astarte. In this ridge of Dakota sandstone, on the southern side, 
Mr. Emmons found a coal-bed ten feet thick, having a brilliant lustre and 
clear black color, and apparently of excellent quality, being altogether free 
from clay or selenite seams. 

Just north of Peoria, on Weber River, overlying the variegated Juras- 
sic shales, appears the Dakota. The basal conglomerate has here increased 
to 200 feet in thickness, the cement being still of the characteristic fine 
quartzitic material, while the pebbles have increased to the size of a cobble- 


304 SYSTEMATIC GEOLOGY. 


stone, some even reaching nine inches in diameter. They pass upward 
into light yellow sandstones, from 200 to 250 feet thick, with a very little 
display of blue shale near the middle of the sandstones. The strike here 
is a little north of east, and the dip varies from 50° to 60° northward. The 
total thickness is about 400 feet. 

Up Chalk Creek, about half-way between Coalville and Bear River, 
is a considerable mass of conglomerate trending north-and-south and dipping 
at a high angle to the west. From its position underneath the black shales 
it is considered to belong to the Dakota. A similar outcrop standing verti- 
cally at the Needles, a limited body altogether surrounded by Eocene, from 
lithological resemblance alone is also referred to the Dakota. 

In the Wahsatch, along the divide between Emigration Cafion and 
East Canon Creek the relation between the Cretaceous and underlying rocks 
is certainly very obscure. North of Kimball's the old relation of conformity 
between the Jura and the Cretaceous is distinctly seen. The conglomerate 
at the base of the Dakota is finely displayed at least 100 feet thick and 
carrying large pebbles from the size of a fist to eight inches in diameter 
The ordinary sequence is very clearly shown in the natural section exposed 
in East Canon Creek. In the hills to the north and west, however, the rela- 
tions are obscure. The country is much covered with soil and forest, the 
outcrops are not continuous, and over the older rocks, especially on the 
Mountain Dell road, is seen a conglomerate closely resembling that at the 
base of the Dakota, which rests unconformably upon the whole older series, 
from the Upper Coal Measures up to the Jura. This conglomerate outcrops 
about six miles up from the mouth of Parley’s Canon, on the road to Parley’s 
Park. The discrepancy of angle between the conglomerate and the Trias 
which underlies it amounts to this, that the latter has a high dip, rising to 
60°, while the conglomerates are at an angle of 25° or 80°. Physically 
these conglomerates closely resemble those of the Dakota, and it is notice- 
able that when struck with a hammer the cement and the pebbles break 
with equal ease; a feature I have never observed in the overlying Kocene. 
From this arose the impression which I formerly held very strongly, that 
the Cretaceous was unconformable with the Jura; but the region is one of 
ereat structural disturbance, and the outcrops are insufficient to prove this 


CRETACEOUS. 305 


absolutely ; and since it is an exception to all the other appearances, it is 
perhaps best to await further facts before finally accepting the idea of a 
nonconformity. This conglomerate, however, is lithologically identical with 
that displayed at Peoria, which is unmistakably conformable with the under- 
lying and overlying rocks. 


CoLtorapo Group.—With strict conformity the sandstones of the Da- 
kota are overlaid by the triple group of the Colorado. As stated in the 
opening of this section, the Colorado Group is a combination agreed to be- 
tween Dr Hayden and myself, including the three variable numbers, 2, 3, 
and 4 of the old Meek and Hayden section. The following is a generalized 
section of the occurrence of this group, as shown along the eastern base 
of Colorado Range, counting from the base up: . 


Fort Benton Group (Cretaceous No. 2, M. & H.): 
1. A dark plastic clay series, with varyingly ferruginous and ar- 
gillaceous layers. 
2. Grayish-blue clays, often inclining to black, more or less cal- 
careous toward the top. 
For the whole group, 200 to 450 feet. 


Niobrara Group (Cretaceous No. 3, M. & H.): 

1. Argillaceous limestones, often based directly on the dark shales 
of the Fort Benton, but sometimes merging into it when the upper 
Benton shales are calcareous. 

2. Light, variegated marls, prevailingly yellow, but often charac- 
terized by a variety of brilliant colors. 

3. Yellow, white, and cream-colored marls, with gypsum. 

4. Whitish-gray marls. 

5. Yellow marls and intercalated saccharoidal yellow limestone. 

6. Bluish-gray, soft, earthy beds, partly calcareous and partly ar- 
gillaceous. 

All of these members are extremely variable in thickness, owing 
partly to the irregular compression and partly to the actual change in 


the original deposit, the whole series being from 100 to 200 feet thick. 
20 K 


306 SYSTEMATIC GEOLOGY. 


Fort Pierre Group (Cretaceous No. 4, M. & H.): 
1. Grayish-black carbonaceous shales and marls. 
2. Nearly black arenaceous clays. 
3. Interstratified beds of clay and sand; in many localities the 
clay predominates ; in others the sand. 
Altogether, 250 to 300 feet. 
Total Colorado, 600 to 1,000 feet. 

This combination of the three members of the old Meek and Hayden 
section into a new group is rendered of value for the reason already 
expressed in the opening of this section, namely, the great variableness of the 
three members in detail, but is even more satisfactory in that it gathers into 
one member the great clay formation of the lower Cretaceous. 

The whole Colorado group, composed of these three members, is 
bounded on the upper surface by the heavy sandstones of the Fox Hill, and 
below by the still more compact sandstones of the Dakota. It is essentially 
a great body of shales and clays, divided in the middle by a zone of marls 
and calcareous beds. Its usual mode of weathering is to form a deep trough 
directly upon the back of the inclined Dakota. Whether horizontal or in- 
clined, the outcrop of the Fort Benton is usually below the neighboring 
level. Directly above it the marls and sandstones of the Niobrara group 
offer a greater resistance to erosion, and consequently form a series of slight, 
outcropping ridges, beyond and above which the soft clays of the Fort 
Pierre again form depressions, and the typical appearance is therefore two 
depressions, separated by the hard, ridgy outcrops of the Niobrara. 

The exposures along the eastern base of Laramie Hills, north of the 
railway, are rather slight. But they are always seen wherever any consid- 
erable section is opened across the Colorado, as around the promontory of 
the Chugwater; the stream-bed showing upon its banks numerous exposures 
of soft clays, outlining a low valley of erosion around the harder sandstones 
of the Dakota. On the north-and-south ridge, between Lodge Pole and 
Ilorse creeks, the lower marls of the Niobrara carry immense numbers of 
the genus Ostrea, mainly Ostrea congesta, these making up nearly the whole of 
the rock. The overlying carbonaceous clays of the Fort Pierre carry also 
numbers of the form Baculites ovatus. The same topographical features are 


CRETACEOUS. 307 


traceable from Shelter Bluffs to Wallbach Springs. In both cases, however, 
the uppermost part of the Colorado is unseen, the beds being hidden under- 
neath the overlying Tertiary. 

South of the 41st parallel, from under the escarped edge of the hori- 
zontal Pliocene plateau, appears the whole Colorado series, dipping—if we 
may judge from the Niobrara, which is the only group whose position is 
characteristically shown—about 16° to 18° to the west, while a little east- 
ward the Fort Pierre declines to a dip of 6° or 8°. At Park Station, in 
beds probably belonging to the Niobrara, were found — 


Inoceramus problematicus. 
Inoceramus deformis. 
Inoceramus Barabini. 


From there southward the Colorado outcrop describes a changing curve 
conformable with the sinuosities of strike of the underlying rocks. It va- 
ries from two to three and a half miles in width, and is characterized by a 
rather smooth, grassy plain, defined along the middle at the horizon of the 
Niobrara by successive ridges of marls and limestones, which rise a few 
feet above its level, presenting an escarped face toward the mountains and 
a more gentle inclination toward the plain. Only in certain favored locali- 
ties, where surface-accumulations of soil are insufficient to mask the out- 
cropping beds, or where the shallow erosion of the rivers and stream-beds 
lays them bare, are the shales of the Fort Benton seen; but upon any cross- 
section line the successive ridges of the Niobrara shales can be traced. 
They form a curious topographical feature, because so limited and yet so 
persistent. What is true of the Fort Benton is also true of the Fort Pierre 
shales above the Niobrara. They are often recognized only by the color 
of the earth where vegetation exposes the decomposed shaly surface, or 
where some trivial cut of erosion lays them bare. In certain places the 
upper part of the Fort Benton is extremely calcareous, and then the line of 
separation between it and the calcareous base of the Niobrara becomes im- 
possible. 

There is great variety in the limy and marly beds of the Niobrara. 
One of the most characteristic features is its base, a bluish-gray lime- 


308 SYSTEMATIC GEOLOGY. 


stone intercalated with a few varyingly thick beds of light-colored clays, 
which are frequently fossiliferous. Above the limestones are yellowish 
white and cream-colored gypsiferous marls. The mode of occurrence 
of the gypsum is quite interesting. It is seen occurring as thin sheets 
and lenticular masses parallel to the stratification of the marls, and again 
occupies thin seams of jointing. Often upon the surface of the weathered 
marl-slopes glittering flakes of gypsum are thickly strewn. Above the 
sulphate-bearing marl occurs a deep-yellow marl, having generally a sac- 
charoidal look, and capped by the bluish-gray, soft, earthy beds, which are 
considered the uppermost members of the group. 

From Park’s Ranch southward to La Porte, and from La Porte to Big 
Thompson Creek, these colored marls are seen outcropping at horizons about 
300 feet above the prominent ridge of the Dakota. From the bluish-gray 
limestone, which is the base-member of the Niobrara, we obtained Inocera- 
mus problematicus. Chemical analysis proves this rock to contain 65.93 per 
cent. of carbonate of lime, the residue consisting of fine blue clay. Single 
beds of the overlying marls, even when not more than eight inches thick, 
may be traced outcropping for several miles in a low ridge above the grassy 
level of the plain. At the Big Thompson the marls are seen to describe a 
semicircle around the lower sedimentary beds, curving westwardly into a bay, 
and again trending southeasterly, passing, at the southern edge of our map, 
under the beds of horizontal (Pliocene) conglomerate. 

In the province of the Plains the whole Colorado series is 600 to 700 
feet thick north of the railway, thickening southward until probably it is 
fully 1,000 feet in the region of the Big Thompson, although the accurate 
measurement is exceedingly difficult, if not impossible. There the lower 
shales are always seen conforming to the dip of the Dakota, namely, about 
14° to 20° eastward. A good instance is the dip of 16° shown by the Nio- 
brara, just below La Porte. But a little higher in the series, and a little 
farther east, comes a very decided change of inclination, and the shales 
decline, reaching angles as low as 8° and 5°. This change of dip is alto- 
gether confined at the surface to the soft, flexible shales of the Fort Pierre, 
and is an interesting instance of sharp flexure without dislocation. From 
the character of the underlying beds, it would seem probable that underneath 


CRETACEOUS. 309 


this fiexure their more rigid bodies have suffered actual rupture. The group 
as a whole is highly fossiliferous, yielding, along the eastern base of the 
mountain, the following forms : 


Inoceramus problematicus. 
Inoceramus deformis. 
Inoceramus Barabini. 
Ostrea congesta. 
Scaphites nodosus 
Baculites ovatus. 
Ammonites sp.? 


The lower Fort Pierre yielded Scaphites nodosus and an undetermina- 
ble Inoceramus. The upper outlines of the Fort Pierre, and those of the 
Colorado, are indicated by a mural face of sandstone turned toward the 
mountains, rising only 3, 4, or 5 feet above the surface of the Plains. The 
sandstone strata dip off very gently to the east, and may be traced in a 
slightly sinuous line from Box Elder Creek to the southern limit of the map. 

Laramie Plains, the great depressed region between Colorado and 
Medicine Bow ranges, is essentially a broad level upland of the Colorado 
group of the Cretaceous. On the eastern base of Bellevue Peak, in the 
bay-like recess, the Colorado clays come into direct contact with the 
Archean rocks. For the rest, they overlie the belt of Dakota sandstones 
which sweeps uninterruptedly around the east and south margin of the 
plain and forms a continuous exposure of rock from the region of Sheep 
Mountain north to the northern extremity of our map, the belt varying 
from 12 to 25 miles in width. The valleys of the Big Laramie, Little Lar- 
amie, and Dutton and Rock creeks are eroded through the Colorado shales 
and marls. Their banks are in general rather low, and the exposures are 
decidedly imperfect. Where the North Park road approaches the mountains, 
dark, thinly bedded shales are seen dipping to the north, intercalated with 
impure limestones, more or less varied by arenaceous material. Underlying 
the carbonaceous clays are outcrops of variegated marls rising a few inches 
above the level of the Plains in a manner characteristic of the Niobrara, and 
carrying immense numbers of Ostree congeste. These beds all dip away 


310 SYSTEMATIC GEOLOGY. 


from the mountains from 8° to 15°. Below the light-colored, almost white 
marls are calcareous, slate-colored, muddy rocks, increasingly argillaceous 
as they descend, and gradually losing the caleareous character. ‘These are 
underlaid by brownish rusty sandstones. 

Where the Big Laramie leaves Medicine Bow Range, in bluish-gray 
marls marking the junction of the Fort Benton and Niobrara, occur numer- 
ous Inoceramus problematicus. 

Near Bellevue Peak the same interesting change of dip already men- 
tioned east of the Colorado, recurs in the Fort Pierre horizon. The caleare- 
ous beds of the Niobrara, containing numerous Ostree, decline at gentle 
angles of 8° or 10° to the north, while the Fort Pierre black clays, after 
continuing the angle of the marls for a short distance, rapidly curve into a 
nearly horizontal position. 

At Como and Rock Creek stations the Fort Benton beds are well 
shown, exposing here 350 or 400 feet of dark, more or less carbonaceous 
clays, with intercalations of sandy clay and pure sandstones. The Fort Ben- 
ton at Como carries certain strata strongly impregnated with iron oxyds, fre- 
quently resulting in concretionary structure. These ferruginous bands are 
exceedingly well developed at Rock Creek, where the varying oxydation 
gives to the exposed strata all the alternating colors of volcanic ash. These 
argillaceous iron-stones, thus far of no practical value, may eventually be 
found rich enough to prove valuable as ores of iron. The ferruginous 
strata vary in thickness from a few inches to three feet. Chemically, they 
are argillaceous carbonates, more or less oxydized, effervescing freely under 
acids, and leaving a residuum of clay and sand. After passing the sta- 
tion, Rock Creek continues its course in a sharp cation through the Fort 
Benton clays. A few miles east of Como Station one of the upper sand- 
stone beds of the Fort Benton is compact enough to afford a good building- 
stone, and is used by the railroad company for the construction of culverts 
and other stone work. These sandstones carry numerous but imperfect 
leaves and stems of deciduous trees. 

Within North Park, following the outcrops of the Dakota sandstones 
already described upon the mountain foot-hills, the Colorado group is ex- 
posed to a very great thickness, overlaid at the horizon of its uppermost 


CRETACEOUS. uel 


members by the undisturbed Tertiaries which occupy the main area of the 
park. All three divisions of the Colorado are distinctly seen, though the lime- 
stones and marls of the Niobrara are perhaps less characteristically developed 
than on the eastern slope. The dark clays and ferruginous layers of the 
Fort Benton are capped by a buff and gray limestone which marks the base 
of the Niobrara. This limestone forms an admirable datum-level through- 
out the whole North Park. It has a thickness of only 20 feet, but is 
remarkably persistent, of extremely fine texture, somewhat: siliceous, 
breaking with a fine conchoidal fracture, and when struck with a hammer 
emits a peculiar bituminous odor. It is essentially a bituminous, siliceous 
limestone. The marls directly overlying this, which form the body of the 
Niobrara, are extremely variable in the proportion of lime and sand in their 
composition. At times they are clear marl; again, tolerably pure yellow 
saccharoidal sandstone, with hardly a trace of lime. The Fort Pierre 
group consists of extremely fine black shales, passing into yellowish- 
white sandstones, very friable and roughly bedded, developed to a consid- 
erable thickness, though probably not reaching the base of the Fox Hill. 
These upper beds yield Baculites ovatus and Inoceramus Barabini, forms thus 
far more characteristic of the upper Fort Pierre than of the overlying Fox 
Hill. Throughout these sandstones there is also a considerable proportion 
of intercalated clay-zones, more than we ever observed in the Fort Pierre. 
The entire thickness of the Colorado series as developed here is between 
1,600 and 2,000 feet. The lower members of the group are well exposed 
on the south flanks of Bruin Peak, near Platte River. Overlying the 
lower clays is seen a steep bank of marls and dark, earthy limestones, 
crowded with a species of Ostrea. 

The Colorado beds are also interestingly seen on the southern slope 
of Sentinel Peak, where they incline southward at an angle of 22° to 
25°, overlying a fine development of Dakota sandstones. All along the 
eastern margin of the Park, from Sentinel Peak to East Camp, wherever 
not obscured by soil, the Colorado beds are finely developed. Ordinarily 
the clay and shale portions are hidden by soil and disintegrated clay ; 
but, as usual, the bituminous limestones and overlying marls of the 
Niobrara horizon are traceable with great continuity. At Parkview 


Bil SYSTEMATIC GEOLOGY. 


Peak there are irregular displays of limestone, in great measure masked 
by the outbursts of trachyte, and the exposed masses of Cretaceous sand- 
stone are themselves interrupted by numerous dikes. Here is seen quite 
an exhibition of caustic contact-phenomena. 

The best display of these rocks on the ridge which separates North 
and Middle parks is at Ada Spring, where the clays and marls of the Colo- 
rado are overlaid by the trachytes at the south and overlapped by the 
horizontal Tertiaries at the east, north, and west. The ravines east of Ada 
Spring cut the groups at right-angles, showing the bituminous limestones 
and argillaceous marls of the Niobrara and the overlying intercalations of 
clay and sand belonging to the Fort Pierre. From the lower bed of lime- 
stone was collected a specimen of Inoceramus, together with an oyster that 
Professor Meek ascribes to the Fort Benton horizon. The marls here are 
not above 150 feet thick, and pass into yellowish-gray shales above. ‘The 
Colorado group is also well displayed at the eastern base of Ethel Peak 
and on the foot-hills north of Crawley Butte. 

South of the uplift at Como the clays and marls of the Colorado cover 
the whole plain in a southwesterly direction, occupying the valley of the 
Medicine Bow, or rather the southern half of its water-shed, and filling a 
deep reéntering bay between Rock and Elk mountains. Around the 
northern base of the sedimentary series of Elk Mountain, the Colorado, 
or at least its lowest members, continues as far as Rattlesnake Pass, where 
the horizontal Tertiaries of the Platte overlap it. It is interesting to 
observe the mode of overlap of the Colorado. At Rattlesnake Creek it lies 
at the base of the slope of the hard Dakota sandstones, separated from the 
Archean mass by the Jura, Trias, and Carboniferous limestones; but 
sweeping around to the northeast point of Elk Mountain it gradually over- 
laps all the other formations and comes directly into contact with the 
Archean, maintaining this contact around to the northwestern point of 
Rock Mountain, and forming a deep bay through which the upper waters 
of Medicine Bow River have their course for twelve or thirteen miles. An 
interesting topographical feature of the Cretaceous in this region is the 
manner in which Medicine Bow River flows northward through the easily 
eroded beds of the Colorado till it reaches a mural escarpment of the over- 


CRETACEOUS. 34) Ls 


lying Fox Hill sandstones, whose harder material forms a barrier to its 
farther northern flow, and deflects it into an easterly and northeasterly 
direction; the river, after it encounters the Fox Hill, following approxi- 
mately the contact-line between that formation and the Colorado. The 
exposures of the Colorado beds through this region are very variable, but 
on the whole sufficient to make out clearly their presence and relations. 

Just north of Medicine Bow Station the beds strike north 65° to 70° 
west, and dip 17° to 18° southwest. Here the white marls of the Niobrara 
yield Ostrea congesta, with an imperfect Inoceramus ; and below the Niobrara 
series, in the sandy beds of the Fort Benton, occur Inoceramus altus and, a 
little higher in the series, Scaphites Warrenianus. Northwest of Elk Moun- 
tain the recognizable portion of the Niobrara between the two sets of clays 
appears to be hardly more than 100 feet thick. Northwest of Sheep Butte 
and south of Rattlesnake Road the Fort Benton beds are present, carrying 
a high proportion of ferruginous clays. The iron here is in concretionary 
and lenticular masses, black and brownish-black, with a conchoidal fracture 
and a hardness of 4. Throughout the cracks and fissures of these ferru- 
ginous clay-stones there is more or less spathic iron and a good deal of ear- 
bonate of lime Besides this, the whole formation is varyingly character- 
ized by carbonaceous matter in clays. A specimen of this clay-iron is 
analyzed in the table of chemical constitution of stratified rocks. Although 
rich enough for smelting, it nowhere occurs here of workable magnitude. 
The strike north of Elk Mountain is north 35° to 40° east, dipping 52° to 
57° northwest. 

Under the conglomerates which cap the northern edge of Savory 
Plateau appears a mass of conglomerate-bearing sandstone, evidently the 
Dakota Cretaceous, dipping in such a manner as to show a local qua- 
quaversal uplift. The conglomerates dip at a slope of 55°, the angle 
declining as they descend into the valley. Following down a line from 
the northern point of the plateau directly across Sage Valley, the con- 
glomerates and sandstones are overlaid by blue clay-shales, followed by 
thin-bedded sandstones and interstratified clays. These are succeeded 
by yellowish-brown, concretion-bearing sandstones, considerably cal- 
careous, followed by 100 feet of blue and white clays containing thin lime- 


314 SYSTEMATIC GEOLOGY. 


stone beds full of Ostrea congesta. A little way above is a second thin, shaly 
limestone, also abounding in Ostrea congesta, and characterized by the pres- 
ence of much aragonite. It would seem here that the sharp division-line 
found so often between the Benton and the Niobrara is wanting, and that 
the former is prevailingly calcareous at the top, the line being impossible to 
draw, as is so often the case along the Laramie Hills. Over this calcareous 
region the character of the soil shows that the Fort Pierre clays are present, 
although their attitude is masked. Along the northwestern side of Bridger’s 
Pass and the northern side of Sage Creek the area of the Colorado beds is 
sharply defined by a mural face of the Fox Hill sandstone, which future 
description will show to be of great geological importance. 

Around the quaquaversal uplift of Rawlings the Colorado beds occupy 
the base of the slope. 

North of Hantz Peak outcrops a considerable mass of conglomerate- 
bearing sandstone, almost a quartzite, overlaid by shales, which are sur- 
rounded and almost overlaid by the trachytes of Steves’s Ridge. There is evi- 
dence of a great deal of local crumpling againstthe Archean; and in some ver- 
tical shales, doubtless of the Colorado group, were obtained unidentifiable spe- 
cies of Ostrea and Inoceramus. Farther down the river the shales of the Colo- 
rado overlap the Dakota and come directly into contact with the Archean. 
Outerops are never continuous, but they consist of blue and drab shales, and 
slight developments of marl, the whole overlaid westward by the grayish- 
white sandstones of the Fox Hill. Between the isolated trachyte body 
known as Sugar Loaf Peak and the Archzean is a local anticlinal of which 
the lowermost exposure is Jurassic, capped by the sandstones of the Dakota, 
and those by the shales of the Colorado. 

The exposures of Cretaceous along the northern slopes of the Uinta 
are confined to three areas—the eastern end of the O-wi-yu-kuts Plateau, 
a region extending from Bruce’s Mountain to Mount Corson, and the ex- 
treme western end of the range at Kamas Prairie. 

At Vermilion Creek the clays of the Colorado, with the middle zone of 
the marly Niobrara limestones, are seen overlying the Dakota conglomerates 
and sandstones. The outcrops form a series of smooth, clayey ridges, from 
1,500 to 1,800 feet in thickness. 


CRETACEOUS. 315 


Where Green River enters the Uinta, over a broad region extending 
twelve or fifteen miles on each side of the river, and from four to six 
miles in a north-and-south line, the overlying Tertiaries have been 
eroded away, showing the whole series of sedimentary beds from the 
Weber quartzites up to the higher members of the Cretaceous. Overly- 
ing the Dakota, which is here expanded to about 450 feet, and contains 
within the sandstone the prominent body of blue shale already described, 
the flat plain country to the north is composed of a broad exposure 
of Colorado beds. They are for the most part covered with soil, but 
here and there the lateral ravines on the immediate foot-hills display the 
contact between the upper sandstone of the Dakota and the blue Fort 
Benton shales. The latter are here remarkably fine-grained and papery in 
structure. They carry fish-scales and fragments of fish vertebrae, and are 
overlaid by the calcareous Niobrara zone which comes to the surface in 
yellow and gray marls and sandy limestones. The line of demarkation 
between the Benton and the Niobrara is altogether obscure, and the region 
as a whole serves only to show that the Colorado group is persistent to this 
longitude, and is here fully 1,800 feet thick. 

Around the southern and western margins of the Yampa Plateau its 
complicated orographical boundaries are bordered by sinuous outcrops of 
Cretaceous, as shown upon the map. The troughs which lie between the 
prominent anticlinal projections are altogether composed of softer beds of 
the Colorado Cretaceous, which extend down Green River for several miles, 
and form an important area drained by the lower parts of Brush and 
Ashley creeks. Upon Ashley Creek, directly above the Dakota sandstones 
and conglomerates which here rest upon the soft shales of the Jurassic, are 
about 100 feet of blue-clay slates, forming the base of the Fort Benton, 
which passes upward into a brownish sandstone yielding the following 


fossils: 
Inoceramus Ellioti. 


Cardium, n. sp. 
Lucina or Astarte. 


On the southern face of the ridge, on the top of this yellow and white 
sandstone, was found a seam of coal ten feet thick, of remarkably good 


316 SYSTEMATIC GEOLOGY. 


quality Above this the succession of clays and marls is obscured by 
débris. Where the Indian trail crosses Brush Creek this coal recurs at a 
corresponding horizon, fossils characteristic of the Colorado group being 
found both above and below the coal-bed. The strata enclosing the 
coal have a dip of 45° to 50° to the northeast, and represent the southern 
member of the deep synclinal which lies between the Split Mountain 
projection and the main mass of the Uinta. The coal-seam here, as on 
Ashley, is about ten feet thick, and is divided by several seams of 
sandy and argillaceous matter. About 200 feet above this, on the ridge, 
though geologically below it, occurs a second coal-bed, within the limits 
of the Dakota and perhaps not far from its base, although the Jurassic out- 
crops which should mark the horizon of division are here obscure. This 
coal-bed recurs near the western end of the Uinta upon Red Fork. The 
upper part of this stream flows parallel to the strike of the upturned beds, 
and displays the identical coal-seam enclosed in a white, friable sandstone. 
Along the singularly curved ridge constituting the western base of Split 
Mountain, the main coal-seam, which forms a distinct monoclinal trough 
fifteen or twenty feet wide, is bounded by an overlying series of sand- 
stones that contain globular concretions from six to ten feet in diameter, 
which weather out from their loose sandy matrix and cumber the slope. 
These great spheroids are marked with projecting ridges checked off at 
intervals on their surface into meridians and parallels, like a globe. On 
analysis they yield 45 per cent. of carbonate of lime and a consider- 
able proportion of alumina, which was not estimated. The beds here dip 
40° to 50°. Directly overlying the spheriferous sandstone which adjoins 
the coal are the lower clays of the Fort Benton. 

In the angle between the Wahsatch and the Uinta the greater part of 
the area is covered by either horizontal or gently dipping beds of the Ver- 
milion Creek Eocene. In the valleys of Weber River and Chalk Creek, 
and in the hills upon either side of these two lines of erosion, is laid bare a 
considerable area of Cretaceous rocks, as may be readily seen on the map. 
Along the Uinta, as displayed in the valley of Weber River below Peoria, 
the Dakota sandstone, there a conglomerate carrying very heavy beds, is 
overlaid by a broad mass of the Colorado series, which consists only 


CRETACEOUS. ay Le 


partially of the clays and marls that are typical farther away from 
the Wahsatch. It is here characterized rather by sandy than by argil- 
laceous and shaly materials. Although there is a hint of the softer clays, 
they are neither so conspicuous nor so pure as farther east. The dip from the 
high angle of the Dakota, as seen below Peoria, declines to 30° to the north, 
and the valley thence down to Coalville is entirely in the beds which we 
conceive to belong to the horizon of the Colorado. There are several minor 
folds, and a considerable amount of dislocation, the faults having a trend 
nearly at right angles to the strike of the strata. 

Between Rockport and Wanship there is an anticlinal developed in 
the Colorado beds. The strata, which down to that point have dipped 
to the north, rise with a southerly slope, pass over the anticlinal, and again 
incline to the north. Here also occurs an interesting change of strike. The 
parallelism with the Uinta is entirely lost, and at Coalville the beds strike 
only a little east of north, dipping to the northwest. Below the little town 
of Wanship, on the left bank of Weber River, the prevailing beds are a 
mixture of clays locally intercalated in yellow and gray sandstones, with 
some massive white strata carrying pebbles. The beds just above Wanship, 
where they pass under the horizontal Tertiary, are considered to be about 
on the horizon of those exposed at Coalville. The bed of coal which is 
shown at the Spriggs mine, and which appears to have been locally thrown 
to the southeast, recurs on the western bank of the river, and passes above 
Wanship. <A better section is exposed upon the Coalville side of the river. 
The hills to the southwest of the village, which are capped with horizontal 
Tertiary, are much covered with detritus; but in the valley of Chalk 
Creek are exposed at numerous places the black shales and marly beds 
of the Colorado, trending in the region of Coalville to the northeast. 
In passing eastward the strike curves around to a nearly east-and-west 
line, and six miles east of Coalville it is due east-and-west. Again, 
east of Uptown it curves into a nearly north-and-south line; so that 
between Wanship and Castle Rock, on the Union Pacific Railroad, the 
strata make two bends, each nearly at right angles, the northwardly strike 
developed at Coalville recurring south of Castle Rock. These two great 
flexures are accompanied by a series of faults, both longitudinal and 


318 SYSTEMATIC GEOLOGY. 


transverse, which divide the whole exposure into dislocated blocks on a 
grand scale, and render the examination of single sections exceedingly un- 
certain, probably exaggerating our ideas of the local thickness. About a 
mile up Chalk Creek valley, and a quarter of a mile to the north of the 
stream, the rock as exposed on the surface of the spur is a buff and gray 
sandstone, carrying frequent pebble-zones intercalated with thin, laminated 
clays. About 100 feet below the horizon of the Chrisman mine, which is 
evidently the same bed opened in Spriggs’s mine at Coalville, the inter- 
laminated clays and sandstones contain the following fossils : 


Inoceramus problematicus. 
Cardium subcurtum 
Lucina. 

Macrodon. 

Modiola multilinigera. 
Arcopagia Utahensis. 
Corbula. 

Martesia. 

Neritina pisum. 
Turritella Coalvillensis 
Eulima funiculus. 

Fusus (Neptunea?) Gabba. 
Melampus. 


This list is completed from the section of Professor Meek,* although 
most of the species were first collected here by us, and the locality thereby 
brougbt to Meek’s attention. 

Above the coal horizon are yellow sandstones which, both in the regions 
of the Chrisman mine and in the Spriggs mine, carry Inoceramus problematicus 
and Ostrea solenisca. Above this, and forming the valley-bottom at the mouth 
of Chalk Creek, is a thickness of 50 or 60 feet of soft, black clays, which 
represent the lower clays of the Fort Pierre group. Along the northern 
side of the valley, and forming a cliff which rises in the angle of the con- 
fluence of Chalk Creek with Weber River, is a body of sandstone showing 


* Geological Survey of the Territories, 1872, p. 439. 


CRETACEOUS. 319 


a cliff 30 or 40 feet high, and containing casts of Avicula, Cardium, Trape- 
zium, and Tellina. These sandstones are prevailingly white at the bottom 
of the cliff, and at the top are coarser, being yellowish in the middle. 
Following down the strata-backs, on the northern slope of the hill, the ravine 
along the north is composed of clays intercalated with sandstone, the base 
of the second ridge yielding, from sandy beds of a rusty yellow color — 


Avicula gastroides. 
Cardium. 

Tellina. 

Gyrodes depressa. 
Fusus Utahensis. 


This whole group of sandstones, beginning with the Avicula beds above 
the black shales which overlie the black clays carrying Inoceramus prob- 
lematicus, is considered, from lithological resemblance to the Fox Hill beds, 
as developed farther east and northeast, to represent the bottom of that 
eroup. Below that horizon clay-beds recur, though not with the regu- 
larity and volume that we have seen farther east. Still, they form as prom- 
inent a member as do the sandstones; whereas from that horizon upward 
through an exposure of over 3,000 feet the beds are prevailingly sandstones 
which bear a close resemblance to the main body of the Fox Hill farther 
east. With this important stratigraphical change there is a great break in 
the organic remains, the prominent species, Inoceramus problematicus, not 
passing above the top of the Colorado, so far as observed. Inoceramus 
problematicus was also found in Chalk Creek valley, above Uptown, in dark 
clays which apparently represented those that underlie the Spriggs coal-bed. 

The conglomerates of the Dakota form a ‘very powerful feature in East 
‘Cation below Parley’s Park, and are overlaid by a considerable thickness 
of intercalated clay beds, gray sandstones, and conglomerates. From the 
uppermost sandstones, directly where they pass under the horizontal Tertiary, 
were obtained a large number of casts of bivalves in a white, almost quartz- 
itic sandstone immediately overlying a heavy bed of conglomer. ate. They 
are specifically undeterminable, but closely resemble those found in the 
laminated clays and sandstones 100 feet under the Spriggs mine. 


320 SYSTEMATIC GEOLOGY. 


A further outcrop of the Colorado beds is observed near Croydon, 
where a rusty yellow sandstone forms a considerable cliff, underlaid and 
overlaid by dark clays. The fossils obtained from these sandstones, although 
specifically undeterminable, belong to the genera Inoceramus and Macrodon. 

As between the Colorado group, in the Rocky Mountain region, and 
the Wasatch, it will have been perceived that the pure clays and brittle marls 
of the eastern region have in the main given way to sands and conglom- 
erates, and that in the western area coal-beds, which are wanting at the 
east, are frequent all the way through the group. 


Fox Hitt Grovp.—North of the 41st parallel on the Great Plains the 
horizontal Niobrara Pliocenes, in stretching westward, have overlapped all 
the Upper Cretaceous, and the Fort Pierre beds are the uppermost members 
exposed. But south of that parallel the Fox Hill sandstones form a 
broad belt extending from the escarpment of the Tertiary southward to the 
southern limit of the map, along the Plains. In the region of our map this 
belt varies from six to nine miles in width. The partition-plane between the 
Fort Pierre and Fox Hill is the junction of the upper dark clays of the 
former with a rusty, coarse, loose-textured, yellow sandstone of the latter. 
It will be remembered that the upper clay-beds of the Fort Pierre on the 
Plains dip at a very gentle slope, averaging 2° to 4°. Over this the basal 
sandstone of the Fox Hill group shows itself in a low ridge five or six feet 
high, which is traced in a meridional direction southward on the Plains, as 
shown on Geological Map I. This sandstone, in several localities, carries 
the characteristic fossils of the Fox Hill group. They are first found by us 
east of Park Station, about a mile north of Cache la Poudre Creek. Here 
were numerous specimens of Inoceramus, well preserved, including I. Bara- 
bini, associated with Ammonites. The exposures of this belt are always ex- 
tremely limited, outcropping on the slightly undulating plain, which for the 
most part is covered with earth and well grassed, the underlying rock being 
concealed. Occasional outcrops, however, prove the Fox Hill formation to 
be well developed here, with a thickness of 1,200 or 1,500 feet, and to con- 
sist of the ordinary soft, yellow, friable sandstones, rendered impure by more 
or less argillaceous material, and containing distinct but always quantita- 


CRETACEOUS. 321 


tively unimportant beds of clay. The upper 300 feet are a more compact 
sandstone which so far yields no fossils. 

On Laramie Plains the only development of the Fox Hill is that which 
lies to the north and east of the projecting mass of Medicine Bow Range 
marked by Rock and Mill peaks. Here the friable yellow sandstones of 
the Fox Hill overlap the Colorado beds and come directly into contact with 
the Archzan. They form a gentle, sloping plateau, almost horizontal, 
though dipping slightly to the east and extending out from the Archzan 
mass from six to eight miles. Along its outer margin it is clearly seen to 
overlie conformably the sandy beds which there cap the clays of the Fort 
Pierre division of the Colorado. The main color of the Fox Hill sandstones 
is here more reddish than east of the mountains. Directly south of Mill 
Creek is a body of brownish gray sandstones carrying layers of rich car- 
bonaceous shales with seams of coal, the shales reaching three feet in thick- 
ness between massive sandstone beds, the latter yielding a few impressions 
of deciduous leaves. This is a region of extreme local disturbance, the 
strata striking from north 30° to 40° east, and dipping 50° or 60° north. 

Between Cooper and Four Mile creeks, the plateau of Fox Hill sand- 
stones is traversed by two wagon-roads. South of the upper one was found 
a new species of the genus Axinea, described as A. Wyomingensis, occurring 
with Inoceramus Barabini. 'The valley of Rock Creek shows excellent 
exposures of Fox Hill beds, which rise on either side of the stream for about 
300 feet. Knormous numbers of the genus Jnoceramus occur in the sand- 
stones here. ‘To the south of Rock Creek, and between there and Cooper 
Creek, sandstones rather low in the Fox Hill series are seen to be inter- 
calated with various beds of carbonaceous shales, and with unimportant beds 
of lignitic coal. East of Colorado Range the Fox Hill beds contain no 
lignites, and these are the first which have been observed in passing west- 
ward. On the north side of Cooper Creek valley, enclosed in beds of hard 
slaty clay, which are underlaid and overlaid by massive, light-colored sand- 
stones, are further developments of coal. It is clear that these stratigraphi- 
cally underlie the beds which carry the distinct Fox Hill fossils, Zroceramus 
Barabini and others. The Rock Creek coal-outcrops are on the old Over- 
land Stage Road, oceurring in a similar manner to those at Cooper Creek, 

21K 


322 SYSTEMATIC GEOLOGY. 


and on about the same geological horizon. It is singular that these ex- 
tremely promising coal-bearing beds have never been more thoroughly 
explored for commercial purposes. 

By referring to the sheet of general sections in the Atlas, a better idea 
of the relations of the Fox Hill sandstones may be obtained than by follow- 
ing the very complicated structural details shown upon the general maps. 
In the uppermost partial section shown upon the sheet, the division corre- 
sponding to Map I. of the Northern General Section, it will be seen that the 
narrow bed of the Colorado series, in all not over 1,500 feet thick, is capped 
by 7,000 or 8,000 feet of sandstones, of which the Fox Hill forms about 
3,800 feet. These consist of red and yellow rusty sandstones, characterized 
by a good deal of ferruginous material, varyingly coarse, almost always of 
loose texture, and carrying throughout the whole extent limited and irregu- 
lar beds of shales and clays, some carbonaceous, others highly calcareous. 
It will be seen how these heavy masses of sandstone come to the surface 
near Medicine Bow Range and against the sides of the anticlinal of Raw- 
lings Peak. 

From Medicine Bow Station they form the surface to within three 
miles of Carbon. Along that line all the beds dip westward. The surface is 
a gently rolling country, with occasional sharp edges of sandstone rising 
a few inches or a few feet above the plain. The base of the series con- 
sists of coarse yellowish beds interstratified with ferruginous clays, shales, 
black carbonaceous clays, and steel-gray-colored beds, the clay intercala- 
tions being an insignificant part of the great sandstone group. 

In the region of Carbon, the Fox Hill sandstones are very well devel- 
oped, and dip from every direction inward toward the town. ‘To the south- 
west they are well exposed in Simpson’s Ridge, where they rise 800 feet 
above the village. The general trend of this ridge is north-and-south, and 
it is built of an imperfect anticlinal, the beds on the eastern side dipping 
eastward at 50° or 60°, while upon the opposite side they incline westward 
at 35° or 40°. In the axis of the fold are seen some medium-grained, 
pearl-gray sandstones, passing upward into arenaceous clays, characterized 
by the presence of a considerable amount of iron, the following subdivis- 


ions being noted : 


CRETACEOUS. 323 


. Thinly laminated arenaceous clay. 


Doe 


Rusty sandstones with ferruginous seams. 
Ferruginous fine-grained clay-stone, 4 feet. 
Fine black clay, 50 feet. 

. Ferruginous clay-stone, 3 feet. 


Sm Se 


So) Ox 


. Crumbling, rusty sandstone. 


Overlying the last member are white sandstones, passing into red. 
North of the railway and east of the North Platte is a noticeable ridge 
having a monoclinal structure, dipping to the northeast, and composed of 
Fox Hill sandstones. Below Fort Steele this ridge determines the course 
of the river, exactly as the Fox Hill bluffs to the east have deflected the 
Medicine Bow from its normal direction. 

The characteristic feature of the outcrop of the Fox Hill throughout 
all this region of Wyoming is the bold bluffs of massive sandstone stand- 
ing out in powerful escarpments above the always topographically lower 
areas of the Colorado clays. These bluffs, as in the case of Separation Peak, 
rise 1,000 feet above the clays of the Colorado. ‘The maximum thickness of 
the Fox Hill here cannot be less than 3,500 to 4,000 feet. There are a 
few casts of Inoceramus and Baculites, together with some plant remains. 

A section across the ridge on the western side of the Platte, south of 
Fort Steele, shows that the lower 2,00J feet are principally beds of mass- 
ive sandstone, 50 or 100 feet thick, with but very little shale. Above 
these are about 1,500 feet of more thinly bedded sandstones, whose individ- 
ual members vary from five to fifteen feet in thickness, and contain a great 
many interlaminated shales, which are often bituminous, and thin seams 
of coal. In the valley south of the ridge, south of Fort Steele, the younger 
sandstones are decidedly ferruginous, show a considerable change of char- 
acter, and are supposed to represent the bottom of the Laramie. ‘The 
entire Fox Hill here is estimated at about 8,500 feet. About four miles 
northeast of Fort Steele the river cuts a cation through nearly horizontal 
beds of the Fox Hill. A friable yellow sandstone, shown about thirty 
feet above the river level, is rich in fossils of the genus Ostrea. 

The middle of the interesting oval uplift of Bitter Creek quaquaver- 
sal is occupied by a Quaternary valley, whose longer expanse is with the 


324 SYSTEMATIC GEOLOGY. 


axis of upheaval, north-and-south. It is crossed diagonally by the valley 
of Bitter Creek. The lowest Cretaceous exposures, which are laid bare in 
the middle of this upheaval, are obscure occurrences of shaly beds of the 
Colorado, which, for the most part, are covered with Quaternary débris, but 
outcrop in the little hill in the middle of the valley, and on the south, toward 
Quaking Asp Mountain, constitute a considerable area, although they are 
to a large extent concealed by more recent débris. Around this nucleus of 
the Colorado are traced, in irregular but nearly continuous concentric ovals, 
the outcrops of the Fox Hill, and over them those of the Laramie. On the 
eastern side of this oval body the dips are from 5° to 7° to the east, as 
shown by the railway-cuts from Black Butte to Salt Wells. On the oppo- 
site side they decline to the west from 12° to 15°, as seen in the region of 
Rock Springs, while toward the south, beyond Quaking Asp Mountain, the 
outcrops of Laramie sandstones dip 25° to 30° to the southwest. 

About six miles east of Rock Springs is seen a compact sandstone of 
almost quartzitic nature, containing casts of Ammonites, Cardium, and Inoce- 
ramus, specifically undeterminable. This is overlaid by coarse gray sand- 
stones, dipping 13° to the west. Continuing down in the series, the Fox 
Hill beds quickly pass under the Quaternary. In the region of Quaking Asp 
Mountain is a fine display of Fox Hill sandstones. This peak is quite a 
plateau-like summit, made of sandstones dipping southwest and striking 
northwest. They are decidedly compact. The central Quaternary plain is 
edged upon the southwest by a line of bluffs referred to the Fox Hill. Again, 
north of Salt Wells Station the Fox Hill beds describe an oval curve, with 
the convexity to the north, and there contain fragments of Ammonites and 
Inoceramus. The upper strata of the I*ox Hill, where they approach the 
Laramie group here, are often very thinly bedded, and show a tendency to 
split up into broad flakes like flagstones. They are also more compact than 
the overlying Laramie series. Coal-seams are decidedly infrequent, and the 
presence of Ammonites, Baculites, and Inoceramus is confined to the Fox 
Hill series. Reckoning by the average dip and width of outcrop, the trans- 
verse section of the Fox Hill here gives about 3,000 feet. In the sand- 
stones east of Salt Wells is found a compact, green, argillaceous rock, 


close-grained and lithologically not far removed from one already de- 


CRETACEOUS. BAD, 


scribed on the eastern side of the Platte at Fort Steele, and in Oyster Ridge. 
It is a slightly caleareous clay-rock, and is not seen in the Laramie. 

From Bear River City, on the Union Pacific Railroad, in the southwest- 
ern corner of Wyoming, is an exposure of the narrow crest of an anticlinal 
of Cretaceous, called Oyster Ridge, which, with the exception of slight inter- 
vals, where it is masked by overlying unconformable Eocene rocks, continues 
to the northwest for 50 miles, passing beyond the limit of our map north of 
Ham’s Hill. The chief exposures are at Bear River City and in the valleys 
eroded by Ham’s Fork and the Little Muddy. In general, thisis a long, nar- 
row chain of outcrops, partly an exposure of the axial region and partly rocks 
of the western half of the fold. The strike of the bed varies from north 30° 
east to due north. There is evidence of a considerable amount of faulting and 
a good deal of erosion before the deposition of the overlying Eocene Tertia- 
ries. At Ham’s Hill the Fox Hill series are exposed as massive sandstones and 
intercalated sandy shales dipping 20° to the west. Farther north, and be- 
yond the limit of our map, on Fontanelle Creek, the axis of this anticlinal is 
observed, showing that it is a very long, persistent fold. Where the Little 
Muddy cuts through Oyster Ridge the Fox Hill sandstones are again seen 
dipping to the west and striking north 15° east. In a little shallow valley 
within Oyster Ridge some disintegrated clay-beds are seen, succeeded along 
the east by the Fox Hills, dipping easterly. They are undoubtedly the 
upper members of the Colorado series, occupying the crest of the anticlinal ; 
the Fox Hill, which has been eroded from over them, dipping to the east 
and west of them. Nowhere else in Oyster Ridge has the eastern mem- 
ber of the fold been observed. In this ridge Ostrea solenisca forms solid 
beds of great thickness, the individual shells reaching twelve inches in 
length. The sandstones contain some peculiar intercalations of siliceous 
clay-slate made up of fine grains of pellucid quartz in a clayey matrix. At 
the extreme southern end of the long, longitudinal valley of the south fork 
of the Little Muddy, the stream-bed occupies a synclinal trough in the Fox 
Hillsandstones, which seems to be a minor secondary synclinal on the western 
flank of the main upheaval. There is a good deal of local disturbance, and 
at the southern end of the valley the rocks on the western side of the syn- 
clinal dip to the east at an angle of 45°. At the very upper end of the valley 


326 SYSTEMATIC GEOLOGY. 


they dip from both sides 60° toward the centre. Some clays underlying 
the lowest Fox Hill on the eastern side of the synclinal contain Cardiun 
auperculum. 'The clays out of which these fossils were obtained have been 
bored for petroleum, and a small amount of it has been obtained. They are 
doubtless the upper members of the Colorado, and are only mentioned here 
as forming the lower boundary of the Fox Hill. East of this, again, are 
found the regular western-dipping Fox Hill sandstones, the continuation of 
Oyster Ridge, which here incline 20° to the west, carrying a twenty- 
foot vein of coal. The reference of these beds to the Fox Hill, however, is 
rendered somewhat uncertain by the amount of local faulting. It is quite 
possible that the sandstones belong to the Colorado, and that the coal cor- 
responds to that found on the southern slope of the Uinta, and indeed at 
Coalville. 

The southward continuation of this series, after an interruption of a 
few miles by overlying Tertiaries, reappears at Aspen, on the railway. 
Here over the Colorado clays, which are well developed, carrying fish-bones 
and fragments of Ammonites, besides beds of grayish limestone which mark 
the Niobrara horizon, the sandstones of the Fox Hill are well exposed, 
dipping from 10° to 15° westward, carrying numerous Ostrea solenisca. 

At Bear River City the hills to the north and west of the station are 
formed of heavy whitish sandstones, standing nearly perpendicular and 
enclosing several beds of coal. The sandstones are rich in Inoceramus 
problematicus and some undetermined univalves. Above the Colorado clays 
the exposure of these sandstones amounts to 7,000 or 8,000 feet in thickness. 
They are for the most part white, though occasionally inclining to brown, 
and carry at intervals beds of heavy conglomerate and irregular inter- 
calations of clay. Of this whole mass about 3,000 to 3,500 feet are assigned 
to the Fox Hill series. 

The Big Horn Ridge, an interesting topographical feature east of 
Green River, near where it enters the Uinta Mountains, consists of the 
full series of the Fox Hill sandstones overlying the soft intercalated 
clays and marls of the Colorado, which occupy a broad valley depression 
between the ridge and the slopes of the Uinta, which are here of the solid 
Dakota sandstones at the base of the Cretaceous. The Fox Hill sandstones 


CRETACEOUS. 327 


are sharply defined at the base by the clays and clayey shales of the Colo- 
rado, and are bounded in the ascending series by the rusty red sandstones 
of the Laramie, but are partly margined on their northern flank by the 
Eocene, which overlaps the greater part of the Laramie series. The pow- 
erful Fox Hill sandstones passing eastward are faulted down into contact 
with the Red Creek Archean at one point, where their average dip of 25° 
to the north is suddenly increased to a vertical position ; and farther east- 
ward they are again underlaid by the Colorado beds, and near Bruce Moun- 
tain pass finally under the overlapping Eocene beds. South of Big Horn 
Ridge and in the clays near Green River the upper part of the Colorado 
formation yielded Baculites and Inoceramus of undeterminable species. 
The Fox Hill in the Big Horn ridges is hardly less than 3,300 feet thick. 

The only considerable exposure of this group south of the Uinta 
within our belt is at Wansit’s Ridge, where, over the Colorado clays and 
sandy shales, is a brown shaly sandstone passing up into 100 feet of white 
massive sandstones, overlaid by 50 feet of bituminous sandstone, the latter a 
greenish, coarse-grained rock, over which are 50 feet more of sandstones 
slightly bituminous. This bituminous sandstone is a very peculiar occur- 
rence, not observed elsewhere in the Cretaceous of the Fortieth Parallel. 
Seen upon the weathered surface, the rocks present the ordinary appear- 
ance of a light yellowish sandstone, but the fracture is pitchy black. A 
specimen analyzed yielded 11 per cent. of bituminous matter and 85.5 of 
silica. These beds strike 20° south of east and dip 20° to the southwest. 
They recur on the eastern side of Green River, forming ridges along the 
valley of White River. 

In the section exposed at Coalville the boundaries of the various mem- 
bers of the Colorado are no longer distinguishable. The shales are con- 
stantly interrupted by sheets of sandstone, which here form decidedly the 
predominating feature. The immense beds of black clays of the Fort 
Pierre and Fort Benton, which along the eastern part of the Uinta are so 
easily distinguishable, are here so subdivided by sheets of sandstone as 
to be no longer clearly recognizable. Moreover, the characteristic limy zones 
of the Niobrara are not observed. Directly north of Coalville, on the 


north face of the first ridge, in the shales which overlie it, and in a yellow- 


328 SYSTEMATIC GEOLOGY. 


ish-gray sandstone, are specimens of Inoceramus problematicus, which have 
been assigned by Professor Meek to the horizon of the Niobrara, and were 
not supposed to pass above it. It would seem here that it must have a 
higher range and pass up into the Fort Pierre. Be this as it may, the alter- 
nation of clays, shales, and sandstones continues upward in the series from 
the Inoceramus problematicus bed for about 280 feet. At that point occurs a 
heavy, massive bed of whitish sandstone, carrying Ostrea solenisca and 
Cardium. 'This appears to be the lowest horizon of the Ostrea solenisca, 
and corresponds to the uppermost level of the main intercalations of sand 
and clay. I am inclined to regard the 280 feet above the Inoceramus prob- 
lematicus clays which closely overlie the Spriggs coal-vein as equivalent to 
the Fort Pierre, and to draw the base line of the Fox Hill at the bottom of 
the heavy white Ostrea solenisca sandstones. These sandstones occur on 
the northwestern side of the valley beyond the first ridge north of Coalville, 
and are seen on the southern base of the second ridge. From that point 
upward there is an exposure of 3,000 feet, chiefly sandstones, though more 
or less intercalated with local clay and shale-beds of moderate dimensions 
and some considerable sheets of conglomerate. About 800 feet up in the 
series, on the face of the third ridge, overlaid and underlaid by sandstones, 
occurs a dark clay-shale, containing the interesting mixture of marine and 
fresh-water fossils so fully described by Professor Meek. The list which is 
made up from his collection and ours includes — 


Anomia, 
Inoceramus, and 
Cardium, 


and is reénforced on the opposite side of the river, where the same horizon 
is again identified at the Carleton Mine, by — 

Unio, 

Cyrena Carletoni, 

Neritina Bannisteri, 

Neritina (Dostia?) bellatula, 

Neritina (Dostia?) carditiformis, 

Eulima chrysalis, 


CRETACEOUS. 329 


Eulima inconspicua, 
Turritella spironema, 
Melampus antiquus, 

Physa, and 

Valvata. 


The occurrence of such an association of fossils, with distinct marine 
forms above and below them, requires no remote explanation. We are here 
close to the original shore of the Cretaceous ocean; immediately westward, 
beyond the longitude of the Wahsatch, lay the continent from which 
these sediments were derived. Evidences of deep-water deposition are 
unfailingly observed wherever the lower part of the Colorado group is 
exposed in this neighborhood. There is equal evidence of increasing shal- 
lowness, with frequently varied sediment during the upper part of the Col- 
orado. Throughout the Fox Hill limited sheets of clays, local conglomer- 
ates, sandstones, and shales are intercalated. For the explanation of these 
fresh-water forms embedded in marine strata it is superfluous to argue an 
elevation of the marine beds. It is entirely unnecessary to suppose any- 
thing more than the washing in of fluviatile shells, exactly as to-day any- 
where on the Atlantic coast the river species are swept out through the 
estuaries, and mingle with true marine forms. The real point of interest 
about these fresh-water shells is the marked aflinities with known Tertiary 
types. If found by themselves, dissociated from the acknowledged marine 
Cretaceous forms, they might have been referred by almost any paleontol- 
ogist to the Tertiary age. Oceanic conditions, by the variations of the 
general marine area and consequent shallowing or deepening of pelagic 
basins and the ever-increasing salinity, should more powerfully modify 
marine species than the fresh waters of continental rivers would their forms. 
The early differentiation of fresh-water types should create no surprise, and 
the discovery of this singularly Tertiary-like group deep in the Cretaceous 
should no more than open our eyes to the early specialization of fresh-water 
molluscan types. Above the horizon of these shells are about 1,000 feet of 
gray sandstones, the lower portion of which carries at several horizons com- 
pacted masses of Ostrea solenisca, both casts and shells. At the upper part 
of the 1,000 feet, in a soft gray sandstone, are indistinct Inoceramus, Ostrea, 
and Cardium. 


330 SYSTEMATIC GEOLOGY. 


On the southern slope of the high hill directly south of the mouth of 
Echo Canon are seen the last members of the conformable Cretaceous series 
in this region. They consist of an exposure of about 700 feet of a pink, red, 
and striped mixture of conglomerates and sandstones, with a few shaly inter- 
calations. These I refer to the base of the Laramie. The exposure of lox 
Hill, therefore, as shown in this section between Coalville and Echo City, 
embraces about 3,000 feet of rocks, for the most part gray, buff, and yellow 
sandstones, carrying purely marine Cretaceous types to the very upper- 
most edge, where, however, the chronologically rather valueless forms of 
Ostrea abound. One thousand feet up in the series lies the group of 
coal-beds opened at the Carleton Mine, both underlaid and overlaid by 
distinct Cretaceous types, and carrying the admixture of fresh-water 
Cretaceous shells already mentioned. In this whole series the species 
Inoceramus problematicus does not occur, but there are two other species of 
Inocerami. 

Ferruginous beds, which have been heretofore described in the Fox 
Hill, occur about 1,000 feet from the base of the series. North of Echo 
City the Eocene conglomerates and sandstones which cover that region are 
eroded away on both sides of the river, displaying an almost continuous 
outcrop of Cretaceous from a mile north of the town to Croydon. The con- 
glomerates which first make their appearance in the neighborhood of 
Witch’s Rocks are supposed to be correlated with the conglomerates which 
along the Wahsatch mark the base of the Laramie. For three miles after 
passing Witch’s Rocks, the mixed sandstones and shales of the Fox 
Hill, which here have a predominant buff color, are exposed along the right 
bank of the river, the hill-slopes above being made of the horizontal 
Eocene. The edges of the Cretaceous strata are presented to the valley, and 
it is chiefly the harder or sandstone portions which come to the surface 
through the débris that has rolled down from the Eocene. In general, the 
type of rocks is a reduplication of that exposed south of Echo Canon. Innu- 
merable oysters occur near the upper regions, and, in descending, Inoce- 
rami and Corbule make their appearance, together with a large number 
of indistinguishable bivalves. The occurrence of conglomerates is here 
even more noticeable than south of Echo Canon. 


CRETACEOUS. Beal 


Laramie Grour.—Throughout the whole Cretaceous, up to the upper 
limit of the Fox Hill group, there is among the geologists who have lately 
studied these formations, so far as I know, neither doubt nor dispute. With the 
exception of a few instances—where purely fresh-water fossils occur, both 
underlaid and overlaid by marine Cretaceous forms, and therefore clearly 
referable to that age—all the series from the top of the Jura to the top of the 
Fox Hill are characterized by an uninterrupted succession of marine Cre- 
taceous forms. The great sandstone series of the Fox Hill is conformably 
overlaid by a continuation of the sandstones, which attain a thickness of 
from 1,500 to 5,000 feet, varied very greatly in lithological character over 
different areas, but in general characterized by the frequent occurrence of 
workable beds of lignite and innumerable seams of carbonaceous clay. 
The fossil forms which are found in this series have led to a disagreement 
which has now become historic as to the age of the beds. They were at 
first, by Meek and Hayden, held to be distinctly Tertiary. That opinion 
has since been so modified as to lead those gentlemen to designate them as 
beds of transition. On the other hand, Dr. Le Conte, Professor Newberry, 
Professor Stevenson, and Major Powell have all committed themselves to 
the view advanced by me in Volume III. of this series in 1870, that the 
whole of the conformable series is Cretaceous. During the slow gathering 
of the evidence which shall finally turn the scale, I proposed to Dr. Hay- 
den that we adopt a common name for the group, and that each should 
refer it to whatever age his data directed. Accordingly, as mentioned in 
the opening of this chapter, it was amicably agreed between us that this 
series should receive the group name of Laramie, and that it should be held 
to include that series of beds which conformably overlies the Fox Hill. 

As we have seen, the characteristic of the Fox Hill upon the Great 
Plains is that of general lithological uniformity throughout considerable 
stratigraphical depths. These sandstones pass imperceptibly into the 
Laramie group, a series of strata which in this portion of Colorado are 
characterized by the occurrence of numerous workable lignite-beds. It is 
also the Lignitic series of Meek and Hayden in the Upper Missouri section. 
Much greater lithological variation is evident over the area shown on the 


map as Laramie than in the underlying Fox Hill. A great amount of 


332 SYSTEMATIC GEOLOGY. 


argillaceous and shaly intercalations, with some pure clay beds and fre- 
quent carbonaceous shales, is the main characteristic of the Laramie. 
The prevailing colors are deep rusty-yellow, pink, red, and buff The 
position of this series on the Plains shows either a slight dip to the east or 
west or perfect horizontality. In other words, it is a region of slight wave- 
like undulations, the inclination of whose flanks is always under 5° or 6°. 
Since this is the uppermost member of the great conformable series, extend- 
ing upward from the Cambrian base, the upper limit is perhaps never 
reached. About 1,500 feet only are exposed. Below this group there are, so 
far, in this region, no workable deposits of coal, either in the Fox Hill, 
Colorado, or Dakota. Near what we consider to be the base of the Lara- 
mie is a prominent yellowish, friable sandstone, which may be traced north 
and south by a low ridge outcrop, the sandstone carrying beds of coal and 
carbonaceous clay. Six or seven miles west of Carr’s Station, this red 
sandstone is found carrying a bed of coal near where the Cretaceous passes 
under the escarpment of the overlying Pliocene. The strata here dip to the 
east from 8° to12°. The coal-bed itself is more than three feet thick, over- 
laid by blue clay and underlaid by black, carbonaceous clay. The sand- 
stones overlying the coal carry a large number of fossils of the genus Ostrea. 
This red sandstone bed, with its enclosures of coal and clay, continues 
quite down to Cache la Poudre Creek, and is conspicuous in the latitude of 


Park’s Station. Considerably above this horizon of coal—as, for instance, 
on the high bluffs of the Cache la Poudre west of Greeley and Evans, the 
most westerly occurrence being seven or eight miles west of the former 
town, but still far above the horizon of the coal-bearing red sandstone—in 
beds dipping 1° to the east, were found marine Cretaceous fossils. They 
also occur on Lone Tree Creek and Crow Creek. The following types 


have been identified: 
Avicula Nebrascana. 


Nucula cancellata. 
Cardium speciosum. 
Mactra Warreniana. 
In addition to these species collected by us, J. J. Stevenson, from near 
Evans and Platteville, the latter just south of our map, obtained— 


CRETACEOUS. 333 


Ammonites lobatus, 
Mactra alta, 


and an undetermined species of Anchwa. It is admitted that two of these 
forms—Cardium speciosum and Mactra Warreniana—are characteristic of 
the upper part of the Fox Hill series, and therefore this marine series which 
overlies the coal may, with a certain degree of fairness, be considered to 
belong to the upper part of the Fox Hill. All these. fossils, it will be 
observed, are found at points lying west of the Denver Pacific Railway. 
Either the coal-beds mentioned in the red sandstones, which are clearly 
overlaid for a considerable thickness by the sandstone-beds carrying the 
above-described fossils, are Fox Hill (in which case the horizon of the coals 
is brought lower than has been formerly admitted in this region), or else 
the marine Cretaceous forms elsewhere characteristic of the upper part of 
the Fox Hill have lived over into the Laramie or Lignitic period. No 
animal forms have been found by us in connection with the higher coal- 
seams in the Laramie here. The occurrence of this group of fossils at so 
many places above the horizon of the coal-beds of the lower part of Hay- 
den’s Lignitie (now the Laramie) series, in my opinion indicates that Dr. 
Hayden was in error in marking the lowest limit of the Laramie by the 
occurrence of the sandstones and coal-beds. It was very natural that he 
should draw here the line which he had formerly drawn on the Upper Mis- 
souri, establishing the top of the Fox Hill by the lower beds of lignite; 
but since in Utah, Wyoming, and southern Colorado the coal-beds are 
found to descend quite to the base of the Cretaceous, it is evident that no 
egroup-lines can be drawn on the coal-beds, except in the most local and 
restricted way. These marine fossils are so plainly Fox Hill that in my 
judgment they should be included within it, and the base of the Laramie 
moved up so as to exclude the beds which bear them. Thus drawn, the 
upper coal-beds east of the Denver Pacific Railway would be left in the 
Laramie, but the formation would here be characterized by no marine fos- 
sils. In order to prove a marine origin for the whole Laramie series, it 
will be necessary to bring to light new evidence east of any fossiliferous 
beds which we have seen. In spite of the fact that thus far I am not aware 
of the upper part of this series having yielded any marine fossils in this 


304 SYSTEMATIC GEOLOGY. 


region, I am of unwavering opinion that it should be classed as Cretaceous, 
from reasons which will appear later. 

Good exposures of the Laramie group beds may be seen along the rail- 
road just east of Separation Station, where they show the peculiar ashen- 
gray sandstones, containing a considerable development of argillacous beds 
and a great number of coal-seams, and contain plentiful plant-remains, gen- 
erally as leaf-impressions, and frequently also as indistinct and partially 
carbonized stems in the impure sandstones. In the ridge south of this sta- 
tion they dip at an angle of 10° north, but flatten out to the north, assuming 
a practically horizontal position, so that the line between them and the over- 
lying Tertiaries is even more difficult to determine than the exact division 
between them and the underlying I’ox Hill group. Perhaps a better section 
of these beds may be obtained north of Muddy Creek, where they have a 
strike of northeast, and dip 20° northwest. Even here the section is only 
partial, as a gap or valley occurs northwest of Separation Ridge, where it 
is cut by Muddy Creek, and the top of the series is not reached. Counting 
from the top downward, were observed — 


Feet. 
1. Thin brown sandstone (nearly horizontal). 
2; “Whitish-sray sandstone 922222 34-- eee ee eee ee 200 
3. Coal-seam. 
4, Gap. 
5. Sandstones, hard, bright vermilion color, with leaf-impressions. - 20 
6; Sandstones, with clays; coal-seam =< — (132-222 eee 100 
{. Banded red and eray sandstone... 22-2 sees ee 500 
8 White sandstone, rather heavily bedded, with red seam - -- ----- 850 
9, Yellowish sandstones, "with claysi:2 >see ae 1, 000 


Along the western base of Park Range the character of the coun- 
try, consisting generally of flat, gently sloping benches, is unfavorable to 
good geological sections. The Cretaceous beds, which are probably Laramie, 
lie nearly horizontal and are only seen in the deeper cuts of the streams, 
and even here the exposures are much concealed by the gravels of the 


talus slopes. 


CRETACEOUS. 335 


Along Little Snake River, in the banks, are seen the yellow and white 
sandstones with coal-seams, and isolated sections of thin beds of clay and 
sandstone carrying abundant leaf-remains, some bituminous seams, and a 
few fossils having a general resemblance to those of the Bear River City 
beds, but which have not been specifically determined. In lithological 
character, however, these beds are equally unlike the heavy sandstones 
of the Fox Hill, or the coarse gravel and striped arenaceous clay beds of 
the Vermilion Creek Tertiary. In the lower Yampa Valley, where the forma- 
tions lie in broad, gentle undulations, the Laramie has been distinguished 
from the Fox Hill Group by general considerations of its higher geological 
horizon, and by a prevalence of reddish and impure sandstones in the out- 
crops, which are too much covered by surface-accumulations to give de- 
tailed sections. 

Around the irregular oval described by the Fox Hill sandstones of the 
Bitter Creek uplift occurs one of the finest exposures of the Laramie series. 
From about six miles east of Salt Wells Station, on the Pacific Railroad, it 
dips at gentle angles of from 4° to 7° to a little north of east, the strike being 
about north 15° west. A continuous series is exposed as far as Black Butte, 
where, upon the top of the bluff, the Cretaceous passes under the beds of the 
Vermilion Creek, with no appearance of angular nonconformity. The ex- 
posure, judging by the angle of dip and the distance across the line of strike, 
appears to be between 5,000 and 6,000 feet; but from the known slight dis- 
location it is probable that this is partially due to reduplication, and should be 
reduced to between 4,000 and 5,000 feet. Taken as a whole, whether a given 
zone is examined for a considerable distance longitudinally on the strike, 
or observed in cross-section, it is seen to be composed of remarkably varia- 
ble beds of sandy and argillaceous matter. The conformity between the 
cleavable sandstones and bedded masses of the Fox Hill is distinctly 
seen about six miles east of Salt Wells, and may be traced north and south 
in a general way. The two formations pass into each other, and the varia- 
bility which marks both series is characteristic of their plane of junction. 
On the western side of the quaquaversal uplift, the railway exposes the 
Laramie group for about five miles on either side of Rock Spring Station. 
To the east it is seen to overlie conformably the Fox Hill beds already de- 


336 SYSTEMATIC GEOLOGY. 


scribed. This western exposure dips about 14°, striking a little east of 
north, while farther south in the Quaking Asp region it dips as high as 25° 
and has curved around to a northwest strike. We consider the boundary- 
line between the two great groups to consist of a bed of Fox Hill sandstone, 
which carries fragments of Ammonites, whereas that genus has not been 
discovered in the Laramie group, the most of its marine fossils being repre- 
sented by the genus Ostrea. 

As a whole, the Laramie beds are here less compact, more frequently 
iron-stained, and more subject to local concretionary structure than are the 
Fox Hills. There is also more clay, and the Laramie is further character- 
ized by the presence of a large number of beds of coal, fifteen or twenty 
frequently occurring in the course of 1,000 feet. As a whole, the series is 
also distinguished by the frequent occurrence of beds carrying leaf and plant 
remains, particularly in the upper part. 

On the eastern side of the anticlinal the Laramie is in general made up 
of low, broken ridges of coarse, friable sandstone, with a general north-and- 
south trend, but with local disturbances resulting in dips as high as 16° or 
18°. Beginning at the Fox Hill summit, the Ammonite-bearing sandstone, 
four miles east of Salt Wells, the exposure up half-way to Point of Rocks 
consists of rapid alternations of friable rusty and light-colored sandstones, 
drab and gray, yellowish clays, and dark, carbonaceous clays, with im- 
portant coal-seams. In a gray sandstone about three miles below Point of 
Rocks were obtained oysters, Anomia, Corbicula, and Amodiola. My. Ban- 
nister also reports Goniobasis and Corbula. Above this point the coal-beds 
become a very important element in the series, although the same rapid 
alternation of strata is continued. Occasional ripple-marked sandstones are 
observed, and reddish sandstones carrying Ostrea. Passing east from Point 
of Rocks to Hallville, massive sandstones bound the railway valley upon 
the east. At intervals they are striped with gray and drab shale-bands, 
which at times are quite carbonaceous. Continuing to Black Butte, and 
still rising in horizon, is a sequence of the same loose-textured sandstones, 
clays and drab shales, the sandstones marked by occasional carbonaceous 
beds, some thin seams of coal, and occasional beds of Ostrea. At Black 
Butte itself the section shows the upper part of the Laramie beds passing 


CRETACEOUS. 337 


under the Vermilion Creek with little or no nonconformity. The bluff-face 
offers exposures of both gray and yellow sandstone, varied with bluish and 
whitish streaks, carrying five noticeable coal-seams. About half-way up 
from the base of the bluff are some laminated gray and light shales, directly 
over a bed of coal which is about two feet thick. These shales contain 
Ostrea, Anomia, Corbicula, Cyrena, and Goniobasis. About 100 feet from 
the top, in a dark-gray sandstone characterized by the presence of a 
ereat number of leaves and stems, Bannister (and afterward Cope) exhumed 
the remains of a Dinosaurian, Agathaumas sylvestre. The beds of the 
summit of the cliff are believed to be quite conformable with the series 
which carry the Dinosaurian bed. Following this horizon a few miles 
north of Point of Rocks Station, an apparent discrepancy of angle of 
about 2° is seen. From the summit of Black Butte the overlying Tertiaries 
sweep north, south, and east. 

The distinct evidence of the Tertiary age of this series will be presented 
still farther on, in the proper chapter. It is enough here to assert, in follow- 
ing the reference of Cope, that the Cretaceous extends to the top of Black 
Butte. 

The highest coals are seen at Black Butte and Hallville. In the clay- 
seam which caps the highest bed at the latter locality were found Corbicula 
fracta, C. crassateliformis, and a Unio, some of which forms are represented 
in the similar bed overlying the coal of Black Butte Station. Iron pyrites 
accompanies almost all the carbonaceous clays and coal-seams. ‘To its 
decomposition are due the sulphur springs of the neighborhood, and the 
reddish stain which characterizes all the places where the coal-beds have 
suffered spontaneous combustion. ‘T'o the north, in the region of the Leucite 
Hills, the only fossils which have been obtained are Ostrea. In general, the 
sand-rocks, from Black Butte downward through the Laramie series, are more 
intercalated with clay and shale than the Fox Hill. In the corresponding 
section exposed on the western side of the anticlinal, from the entrance of 
Bitter Creek Cation to Rock Springs, were observed the identical alternating 
series of sandstones, shales, and clays, whose special members cannot be 
correlated with the beds on the eastern side with any exactness. Numerous 
coal-beds are exposed, the lowest of which is that opened by the Van Dyke 


22) i 


338 SYSTEMATIC GEOLOGY. 


mine, where there is a bed of four feet of excellent coal, overlaid by red, iron- 
stained beds, containing masses of limonite. This bed is near the base of 
the Laramie group, and not far from the Ammonite sandstones which cap the 
Fox Hill. In the artesian borings at Rock Springs Station no fewer than sev- 
enteen coal-seams were crossed in a depth of 700 feet. The principal bed, 
having a thickness of about eleven feet, dips northwestward at an angle of 15°, 
striking about30° east of north. A few Ostrea and Corbicula, of identical species 
with those found on the eastern side of the anticlinal, are obtained from the 
western meraber. The highest outcrops observed on this side are to the 
north and west of Rock Springs, where, between the base of the bluffs of 
Green River Eocene and the upper members of the Laramie, is interposed 
a thin covering of reddish clayey soil, resulting from the decomposition of 
the upper beds of the Vermilion Creek, which here rest unconformably 
upon the Laramie. The Vermilion beds are not well exposed, but the dis- 
crepancy of angle between the Tertiaries is shown by the difference of dip 
between the Green River, which here has an inclination of 4° to the west, 
and the Cretaceous, which inclines at 12°. 

As to the precise upper limit of the Cretaceous series, the character of 
the sediment, the ambiguity of fossil forms, and the absence of any sharp 
physical break or nonconformity have led to a variety of readings of this 
region. Powell and White draw the line below the Hallville and Black 
Butte coals, leaving these upper beds, including the Dinosaurian and leaf- 
beds of Black Butte, in the Tertiary. They describe a slight “‘noncon- 
formity of erosion,” producing little irregularities in the upper surface of the 
bed directly above the horizon of the Anomia and Odontobasis in the lower 
strata near Point of Rocks. This, however, draws an arbitrary line between 
groups of fossils of close relationship; some of the identical forms occurring in 
their upper Cretaceous appearing in their lower Tertiary at Black Butte. 
Moreover, they disregard entirely the evidence of the Dinosaurian, which 
would seem to be conclusive proof of Cretaceous age. We prefer to draw the 
line on the top of Black Butte, including the Dinosaurian and plant-beds in the 
Cretaceous, believing also that in tracing the contact between the beds next 
over the Dinosaurian series and the ashy beds which overlie them, we detect 
a slight nonconformity which, when traced north, seems both more per- 


CRETACEOUS. 339 


sistent and more observable than the nonconformity of erosion noted by 
Powell, which we fail to follow north. The Vermilion Creek series, which 
here rests upon the top of the Laramie in conformity, is elsewhere seen where 
the nonconformity is violent, the difference of angle reaching often 20° and 
sometimes 80°. 


SECTION IV. 
RECAPITULATION OF THE MESOZOIC SERIES. 


Analytical Geological Map III. accompanying this section shows the 
exposures of all the Mesozoic rocks within the Fortieth Parallel area, 
consisting of the Triassic and Jurassic, and four grand divisions of the Cre- 
taceous. It will be seen that between the Walhsatch Mountains and the 
meridian of 117° 30’ no Mesozoic rocks are laid down. It will further be 
noticed that west of the Wahsatch the Cretaceous is not seen. 

The foregoing detailed description of the leading Mesozoic outcrops will 
have shown that the little Mesozoic province in western Nevada differs 
widely, both as regards the subdivisions of the rocks and the character of 
their fauna, from the broad Mesozoic area east of the Wahsatch. The absence 
of the rocks of middle age over western Utah and eastern Nevada is, at the 
present writing, a problem of little difficulty. The precise relation between 
the Mesozoic and the Palzeozoie rocks in the Wahsatch region and eastward, 
is very clearly seen to be that of entire conformity, there being no cessa- 
tion of conformable deposition, from the lowest Cambrian to the uppermost 
Cretaceous rocks. Wherever the Mesozoic rocks are exposed and deeply 
eroded, the underlying conformable Carboniferous series are invariably seen, 
with the single exception of overlaps where the later Mesozoic series comes 
into contact with Archean masses. In the western Nevada province the 
relations are totally different. There, the Mesozoic series rests directly 
upon a foundation of old Archean mountain ranges, with no intervening 
Paleozoic. The latter rocks end abruptly where the Mesozoic rocks begin, 
and thereafter westward for 200 miles the general structure is that of an 
Archzean foundation, thickly overlaid by Mesozoic beds. The explanation 
of the absence of Mesozoic rocks between the Wahsatch and the meridian of 
117° 30’ might be accounted for in two different ways. First, supposing 
the Mesozoics to have been continuously deposited over the whole interven- 
ing area, in the great subsequent erosion they might have been entirely re- 
moved from the middle country, leaving only the older Paleozoic rocks 

340 


RECAPITULATION OF MESOZOIC. 341 


exposed. Or, secondly, there might have been an upheaval of the country 
between the meridians of 112° and 117° 30’, making a land area at the end 
of the Carboniferous period, and the Mesozoic rocks would then have been 
deposited unconformably in the oceans upon either side of the new land. In 
the latter case we should expect to find some evidence of the unconformable 
relations between the Mesozoic and the older shores. In the case of the 
western line of contact, we have nowhere been able to find the Triassic and 
Carboniferous rocks in contact. But the general stratigraphy of the section 
is such that we feel altogether assured in the belief that they are noncon- 
formable, and that the Palzeozoics never extended beyond their present area. 
But when we come to examine the relation between the Mesozoic and the 
underlying Paleozoic in the Wahsatch, it is found to be that of absolute 
conformity. However, in the very next range westward, that which is made 
up of the Oquirrh, Promontory, and the eastern islands of Salt Lake, the 
Paleozoic rocks are found, but no Mesozoic. The region of Wahsatch 
Range and of the eastern portion of the valley of Salt Lake has been the 
theatre of the most tremendous mechanical violence. It has been repeatedly 
lifted and depressed, faulted and degraded, and although the entire series is 
conformable from Cambrian to uppermost Cretaceous in Wahsatch Range 
itself, the probability is that the exact shore-line lay somewhere in the lon- 
gitude of the present depression of Salt Lake, and that erosion has carried 
away the evidence of a nonconformity which must have existed. 

Another point of difference between the Utah and Wyoming Meso- 
zoic area and that of western Nevada, namely, the absence of Cretaceous 
in the western field, is easily accounted for from the known facts of Cali- 
fornia geology. The great folded and lifted mountain ranges of Triassic 
and Jurassic rocks, which begin in the Fortieth Parallel with Havallah 
Range and extend westward to and include the Sierra Nevada, were all 
upheaved, making at the close of the Jurassic period a great system of 
chains which were at once lifted above the ocean-level. The shore 
was moved westward from 117° 30’ to the western base of the Sierra Ne- 
vada, thus adding a post-Jurassic extension of 280 miles to the continent. 
The Pacific Cretaceous ocean-shore extended, as Whitney has shown, from 
Southern California along the western base of the Sierra, up to the region of 


342 SYSTEMATIC GEOLOGY. 


Mount Shasta, and then, as my observations prove, skirted in a northeast- 
erly direction, touching the west base of the Blue Mountains of Oregon, 
south of Columbia River. Against this post-Jurassic shore the enormous 
Pacific Cretaceous series was conformably laid down. The ancient coast 
is clearly defined by the long line of nonconformable contact traced from 
southern California north to Columbia River. In the western part of 
the Cordilleras, therefore, there is a strict and palpable nonconformity, often 
amounting to a fullright angle, between the Jurassic and the Cretaceous. 

There are some extremely interesting facts to be observed in the 
region where the Paleozoic and Mesozoic approach one another, near the 
117th meridian. When followed from central Nevada up to that longitude, 
the Palzeozoic rocks are seen gradually to thicken, the greatest fragmentary 
members of the conformable Paleozoic series are seen to grow coarser and 
coarser, and to bear more and more angular shore conglomerates up to the 
time when they suddenly give way to Mesozoic rocks. There is no serious 
reason to doubt that at this longitude was the shore of the Archean conti- 
nent, whence was washed down the detrital material that made the frag- 
mentary members of the eastward-stretching sheets of Paleozoic rocks. 
The Paleeozoics resting on an Archean basis come directly up to the 
continental shore with a thickness of over 80,000 feet, in which, from 
the sequence of material, there is abundant evidence of successive sub- 
sidences as indicated by plant-bearing carbonaceous beds and sheets of 
conglomerate. Directly west, resting upon a precisely similar floor of Ar- 
cheean ranges, is the Mesozoic series of about 20,000 feet, superposed upon 
what just previously was the continental land bordering the Paleozoic 
ocean. It therefore becomes evident that in the brief interval of time be- 
tween the uppermost Carboniferous beds and the lowermost Triassic strata 
there was a complete displacement and faulting between the Palzeozoic sea 
and the Archzean continent, by which the beds of the Palzeozoic ocean were 
lifted above sea-level, and the old Archzan continent depressed far below 
sea-level. 

It has been before mentioned that from the interval between the Wah- 
satch and this interesting 117th meridian region, the shales and argillaceous 
limestones of the Permian series have not been found. It is true that 


RECAPITULATION OF MESOZOIC. 343 


as they are very soft and easily disintegrable they might readily have 
been totally removed from the whole surface of the country, and their ab- 
sence to-day may therefore be no proof that they were not deposited con- 
formably over the Coal Measure limestones, as they were east of the 
Wahsatch. If they were deposited, it seems quite possible that the era of 
the great displacement by which the western Archzean continent went down 
and became submerged, took place in Permian time. <A color of proba- 
bility is given to this by the observed symptoms of slight nonconformity 
between the Coal Measure limestones and the Permian already mentioned 
on the flanks of the Wahsatch. It would seem not improbable that the up- 
heaval was made at the beginning of Permian time, and that deposition 
went on continuously east of the upheaved region, namely, east of the 
present Wahsatch; in which case the Permian, if existing in the west, will 
be as an underlying and thus far unexposed member of the conformable 
series, of which the lowest Trias are the lowest present known beds. In 
this remarkable revolution the sea-beds of the Paleozoic emerged and 
became land, while the land went down and formed a deep ocean area, in 
which the sediments thereafter derived from the Paleozoic land-mass were 
accumulated in the thick deposits now seen in the conformable Mesozoic 
series. 

Leaving the subject of the Cretaceous to a later part of this section, 
a brief comparison of the Triassic and Jurassic formations of the two great 
provinces will be here attempted. In the region of the Rocky Mountains 
we have seen that the Trias frequently overlaps the older rocks and comes 
directly into nonconformable contact with the great Archean islands that 
now form the three. ranges of the Rocky Mountain system in our latitude. 
The Trias is in general a series of sandstones; the upper half is always of 
lighter colors than the lower half, and is always intercalated more or less 
with beds of dolomitic limestone and gypsum. The series varies from 300 
to 1,000 feet in thickness. Wherever it stands at a high dip, it is most com- 
pressed in thickness and most compacted in lithological character. Wherever 
its position approaches horizontality, the texture of the rock is that of a loose, 
friable sediment. The lower half of the series is usually from brick to ver- 
milion red, the upper half pale pink, pale red, and buff, with occasional 


344 SYSTEMATIC GEOLOGY. 


exceptions of white and brilliant vermilion. The intercalated dolomitic and 
gypsum beds are never continuous, but are shallow deposits of no great lat- 
eral extension. On appreaching the Archean rocks, the Trias have always 
more or less of local conglomerates, derived directly from the shores against 
which they abut. There is considerable variability in color, in thickness, 
and in the special arrangement and sequence of the sediments. T’rom 1,000 
feet maximum in the region of the Rocky Mountains, the deposit thickens 
in passing westward, until, in the neighborhood of the eastern part of the 
Uinta, it is fully 2,060 or 2,500 feet thick. The division between the lower 
dark-red member and the upper buff or white member is much more distinct 
in the Uinta region than to the east. Here, however, are still the inter- 
calated gypsums or dolomites in the upper half of the series, the gypsum 
sometimes reaching forty feet of pure white crystalline sulphate. There 
are also in the Uinta considerable intercalations of clayey matter, which are 
rare in Colorado. 

Passing still farther westward, against the Wahsatch there is again a 
noticeable diminution of thickness and a corresponding increase of stony 
compactness. Under the microscope, no single specimen was observed that 
had not a considerable amount of carbon and a trace of crystals of carbonate 
of lime. In approaching the Wahsatch, also, there is a sensible increase of 
conglomerates. This constitutes another argument indicating the approach 
of a land-mass to the west, whence detritus is derived. But one fossil, 
a new species, was found in the entire Triassic series of the east, and 


that was obtained from one of the limestone beds—a greenish-drab litho- 
graphic limestone—a little above the middle of the series, on the south flank 
of the Uinta. That fossil had a distinctly upper Triassic or Jurassic facies. 
The upper horizons, especially the uppermost member of all, varying from 
200 feet in the Colorado to 600 in the Uinta, and sometimes more than that 
upon the flanks of the Wahsatch, is characterized by remarkable cross- 
stratification, which is prominent over most of the exposed area east of the 
Wahsatch. The flow-and-plunge structure is developed in a perfection 
rarely seen, the plane of the cross-stratification often inclining to the true 
9RO 


bedding-planes at an angle of 30° to 35 


The upper half, bearing irregular sheets of gypsum and of dolomitic 


RECAPITULATION OF MESOZOIC. 345 


limestone, is always directly conformably overlaid by the Jurassic beds, 
which, when first seen on the east flank of Colorado Range, vary from 250 
to 275 feet in thickness, and increase steadily eastward till, on the flanks 
of the Wahsatch, they have reached fully 1,800 feet. There is a very 
great physical contrast between the general character of the materials 
of the Triassic and the Jurassic series. The former is, on the whole, free 
from lime, except in the sulphate and dolomitic beds, and with the excep- 
tion of certain parts of the Uinta is rather free from intercalated clays. 
On the other hand, the Jurassic, in the Rocky Mountain region, is entirely 
made up of soft clays, argillaceous and calcareous marls and thin intercala- 
tions of fine lithographic limestone. In the Uinta and Wahsatch region 
the lower 600 or 700 feet are a bed of solid but very fine-grained, slightly 
argillaceous limestone, and the upper 800 feet are made of fine calcareous 
argillites. As a whole, the series is a lime and clay deposit. 

In the Rocky Mountain region, and at certain points still farther west, 
it is a little difficult to fix the exact plane of demarkation between Trias and 
Jura. The latter is more sandy at the bottom, the former more limy at the 
top, and they often pass one into the other by insensible gradations. In 
places, as in case of the section exposed in Weber Canon, the limestones 
of the Jurassic rest directly upon indurated, cross-bedded sandstones of the 
Upper Triassic. There is never any doubt as to the upper limits of the 
Jurassic. The soft calcareous and argillitic beds are sharply followed by a 
wonderfully characteristic heavy bed of conglomerate, the base member of 
the Dakota Cretaceous. The maximum development of the Trias and Jura 
in our latitudes east of the Wahsatch is 3,800 feet. 

The Jurassic of the Eastern province is abundantly charged with char- 
acteristic mollusks as far east as Fort Steele, but in eastern Wyoming and 
Colorado in our latitudes there have yet been found no fossil shells. The 
eastern foot-hills of Colorado Range have, however, of late yielded a re- 
markable reptilian fauna of Jurassic types. The upper clay and sandstone 
beds directly under the bottom of the Dakota conglomerate have been called 
by Marsh the Atlantosaurus beds. 

Besides the occurrences in Colorado, important localities are now being 


opened in middle Wyoming. 


346 SYSTEMATIC GEOLOGY. 


In the Atlantosaurus beds of the upper Jurassic the Dinosaur remains 
are the most abundant fossils, and most of them belong to reptiles of gigan- 
tic size. The largest have been found at Morrison and Cation City, Colo- 
rado, and others of huge dimensions at various localities in Wyoming. 
Atlantosaurus immanis, Marsh, had a femur eight feet four inches long, which 
would indicate, if the animal had the same proportions as a crocodile, a 
length of over one hundred feet. Atlantosaurus montanus, Marsh, was nearly 
as large, and both were far larger than any land animal, recent or fossil, 
hitherto discovered. Other huge Dinosaurs from the same horizon are— 
Apatosaurus Ajax, Marsh; Apatosaurus grandis, Marsh; Allosaurus fragilis, 
Marsh; Allosaurus lucaris, Marsh; and Morosaurus impar, Marsh. Creosaurus 
atrox, Marsh, was a smaller carnivorous Dinosaur. With these were 
found two small Dinosaurs of the genus ZLaosaurus, Marsh (L. celer and 
L. gracilis, Marsh), and also the two smallest Dinosaurs known, viz, Nano- 
saurus agilis, Marsh, and N. victor, Marsh, the former about as large as a 
cat. A peculiar reptile, allied to the Dinosaurs, but representing a new 
group, is Stegosaurus armatus, Marsh. The crocodiles are represented in 
this horizon by Diplosaurus felix, Marsh, which had biconcave vertebre. 
There was also among the fishes a species of Ceratodus (C. Giintheri, 
Marsh), 

Under date of May 13, 1878, Marsh announces the further discovery 
from the Wyoming Jurassic of a mammal, a small marsupial, to which he 
has given the name Dryolestes priscus. 

Passing now to the district of western Nevada, the sections, which often 
do not reach the base of the conformable series, expose two distinct, easily 
recognizable groups of the Trias. The Koipato, already described, is made 
up of siliceous and argillaceous beds, whose chemical peculiarity is the almost 
total absence of soda and lime and the high percentage of alumina and 


potash—a series probably derived from the disintegration of the heavy 
Weber Carboniferous quartzite, which must for a long time have constituted 
the main surface of erosion of the newly lifted Mesozoic land. This series 
has an observable thickness of about 6,000 feet, with an unknown quan- 
tity to be added for the bottom, unseen beds. Conformably over the Koi- 


pato is the great Alpine Trias Star Peak series of 10,000 feet, composed of 


RECAPITULATION OF MESOZOIC. 347 


an alternation of three great limestone zones and three interposed quartzite 
zones, the lower quartzite closely following the physical and chemical pecu- 
liarities of the Koipato series below, the upper two quartzites representing 
moderately pure siliceous sediment. The fossils of these limestones, as 
already described, repeat, with marvellous exactness, the facies of the St. 
Cassian and Hallstadt beds of the Austrian Alps. 

Directly overlying the uppermost Star Peak quartzite, the summit 
member of that group of 10,000 feet of strata, is a limestone carrying low 
Jura or Lias forms, and succeeded upward by an immense series of argil- 
lites of unknown thickness. The conformable Mesozoic development, there- 
fore, is here about 20,000 feet. Under the great folds into which this 
series of rocks has been thrown, interesting examples of Archzan peaks 
are found, around which the Triassic beds have been deposited. In some 
instances the partially buried peaks show a height little inferior to the great 
granitic Archean mountains, around and over which the Paleozoic beds 
were laid down. 


With the exception of the Archzan mountain masses of the Rocky 
Mountain group of ranges between the meridians of 105° and 107°, which 
during the deposition of the conformable series from the Cambrian to the 
close of the Cretaceous were islands lifted above the sea, the whole Fortieth 
Parallel area east of the Wahsatch was covered with a very great develop- 
ment of Cretaceous rocks. Against the Wahsatch—that is, against the west- 
ern shore of the ocean—there is a total thickness of from 11,000 to 13,000 
feet, the series gradually thinning eastward until, as exposed east of Colo- 
rado Range, they have been reduced to a thickness of 4,200 to 4,500 feet. 
There is entire conformity between the base of this series and the sum- 
mit of the Jurassic. There is also complete conformity through the whole 
Cretaceous series from bottom to top. All observers have united in the 
common assertion of this absolute conformity up to the close of the Lara- 
mie group. 

The Cretaceous, as defined by the studies of Meek and Hayden, con- 
sists, first, of the Dakota sandstones and conglomerates, being the basal mem- 
ber of the series; secondly, of the group which, as already mentioned, Dr. 


348 SYSTEMATIC GEOLOGY. 


Hayden and I have agreed to call the Colorado, made of his former Cre- 
taceous members, Nos. 2, 3, and 4, namely, the Fort Benton, Niobrara, and 
Fort Pierre groups; thirdly, the Fox Hill group, a heavy body of sand- 
stones. 

Here, with those who follow Hayden, the Cretaceous series comes to 
an end. Conformably over this lies the group which Hayden and I have 
agreed to call the Laramie, which is his Lignitic group, and is considered by 
him as a transition member between Cretaceous and Tertiary. There is no 
difference between us as to the conformity of the Laramie group with the 
underlying Fox Hill. It is simply a question of determination of age upon 
which we differ. 

The basal member or Dakota group consists of a persistent conglom- 
erate of remarkably indurated cement, in which are fine chert pebbles 
the size of filberts in the east, but reaching nine or ten inches diameter 
against the Wahsatch. Over this is a varying series of yellow and gray 
sandstones, with, in the Uinta region, a prominent belt of dark-gray clay 
shales. At the very base of the Dakota, in the Uinta, is a very fine coal- 
bed, which never recurs to the east. 

The Colorado is essentially a group of calcareous shales and clays, with 
a sandy region about the middle of the group, which is made up of cal- 
ciferous sand-rocks, marls, and argillaceous limestones. Above and below 
this lie the dark-clay shales of the Fort Benton and Fort Pierre sub-groups. 
The entire thickness of the Colorado east of the Rocky Mountains is from 
800 to 1,000 feet. At its greatest development in the Uinta and Wahsatch 
it reaches 2,000 feet, and while even there, in the neighborhood of the 
Cretaceous ocean coast, it is still largely made up of the same clay, shales, 
and marls which characterize it in the eastern region, yet it is frequently 
interrupted by considerable sheets of friable, yellow, slightly calciferous 
sandstones. In the Fort Benton shales, the lowest of the three divisions, 
are frequently collected — 

Ostrea congesta, 
Tnoceramus problematicus, 
Prionocyclas Woolgari, and 
Scaphites Warrenensis. 


3ECAPITULATION OF MESOZOIC. 349 


In the middle Niobrara sub-group, usually in heavy beds of chalky 
marl, or in soft arenaceous marls, interlaminated with bituminous lime- 


stones, occur — 
Ostrea congesta, 


Baculites, and 
Inoceramus deformis. 


From the uppermost region of the Fort Pierre, at the plane of its 
contact with the overlying Fox Hill, were obtained Inoceramus Barabini, 
associated with Ammonites. In the region of Coalville, and to the south 
for several miles in the characteristic exposures of the Colorado group, are 
several workable coal-mines. East of Colorado Range there are absolutely 
none at this horizon. With the exception of the region bordering immedi- 
ately on the Wahsatch, the most characteristic point about the whole group 
is the extreme fineness of its sediments, their very great variability, and the 
comparative thinness of their bedding. 

The Fox Hill group, made up almost altogether of gray, rusty, and 
buff sandstones, containing a few earthy, clayey intercalations, reaches a 
development of about 1,500 feet in total thickness on the Great Plains, and 
increases toward the Wahsatch to 3,000 and 4,000 feet in the basin of 
Green River. 

East of the Rocky Mountains the Fox Hill contains but one coal- 
bed, and that at its extreme upper limit. As already indicated in the 
description of the country east of the Rocky Mountains, the lowest coal-bed 
is overlaid by a sandstone carrying marine fossils characteristic of the Fox 
Hill group. In drawing the line upon our map, the division between the 
Fox Hill and the Laramie was made so as to include the lowest coal in the 
Laramie or Lignitie series. The subsequent discovery of these fossils above 
this coal-bed leads me to place the line higher, bringing the summit of the 
Fox Hill group immediately above the sandstone carrying the marine fossils. 

Passing westward to the region of Cooper Creek and Rock Creek, the 
Fox Hill has several considerable beds of coal. Stratigraphically its most 
characteristic features are the enormous beds of gray, white, and pale-buff 
sandstones, which in the basin of Green River form the lowest horizons of 
the Fox Hill. These reach, not infrequently, single beds of fifty or sixty 


350 SYSTEMATIC GEOLOGY. 


feet in thickness, without a shadow of a stratum-plane. In the basin of 
Green River, especially in the Bitter Creek anticlinal, which forms such 
magnificent exposures of the Fox Hill and Laramie group, the former 
carries a great number of coal-beds throughout its whole thickness. In 
the region of Coalville all the workable beds above that of the Spriggs 
Mine are included in the Fox Hill. At the Carleton Mine, very close to 
what must have been the Cretaceous shore, a little group of fresh-water 
shells is intercalated between horizons rich in marine mollusks. So far 
as our observations go, these are the only fresh-water forms anywhere con- 
tained in the Fox Hill group, and they are doubtless attributable to some 
estuarial current which brought down the river species and deposited them 
in the marine muds of the shore, a phenomenon too common on all coasts 
to require further notice. 

The line between the Fox Hill and the Laramie, as drawn upon our 
maps, is based on the cessation of true pelagic forms. It is made on the 
summit sandstone of the Fox Hill, as indicated at various points of the 
map, a stratum containing Ammonites and Inoceramus. Above that hori- 
zon, conformably extends the enormous thickness of the Laramie, a 
series of rather loose sandstones, buff and gray, frequently striped 
with alternating strata of rusty red, and carrying repeated interca- 
lations of carbonaceous clays, and a considerable number of coal-beds. 
This great series, embracing a thickness of over 5,000 feet in the Green 
River Basin, is characterized throughout by molluscan forms which are 
of both salt and brackish-water types, and by several important zones of 
plant-bearing beds, which have yielded abundant flora illustrated with 
great fullness by Mr. Lesquereux. 

Aside from the Taconic system, no single geological feature in all 
America has ever given rise to a more extended controversy than the true 
assignment of the age of this group. On data which will presently be set 
forth, it is assumed by us to be the closing member of the Cretaceous 
series, and the last group of the great conformable system which east of 
the Wahsatch stretches upward from the base of the Cambrian. 

The upheaval of a continental mass at the close of the Carboniferous 
extending from the Wahsatch west of the meridian of 117° 30’, and an 


RECAPITULATION OF MESOZOIC. By 


addition to that continent of a westward extension of 200 miles at the 
close of the Jurassic, left a wide area of land, from which was derived the 
enormous mass of detrital material making up the Cretaceous series. Fully 
four fifths of the 12,000 feet are of sandy materials, which are always 
more or less mingled with fine lime. The shales of the Colorado, and the 
shaly strata which are intercalated in the Fox Hill and Laramie, are all 
highly caleareous; yet it would be safe to say that fully seven tenths of 
the entire material resulted from the destruction of siliceous rocks. 

In regard to the Laramie group, Hayden, Meek, and Lesquereux 
have held: 

First, that it was conformable with the Fox Hill; 

Secondly, that its molluscan fauna indicated a brackish-water origin ; 

Thirdly, that its general facies was more nearly related to the Tertiary 
than to the Cretaceous ; 

Fourthly, that the abundant plant-remains were distinctly Tertiary. 
Lesquereux has divided the Laramie flora into three sub-groups, designated 
after prominent localities, as the Bitter Creek or lower group, the Evanston 
or second group, and the Carbon or third and upper group; referring the 
first of these from its flora to the Eocene, the second generally to the 
Miocene, the third or Carbon to the middle Miocene. 

Fifthly, that the Laramie group passed upward conformably into the 
purely fresh-water Wahsatch group ; 

Sixthly, as expressed in the introductory letter to Volume VII. of the 
“Report of the United States Geological Survey of the Territories,” the 
‘“Wahsatch group as now defined and the Fort Union group are identical 
as a whole, or in part at least”; 

Seventhly, the name “Wahsatch group” was applied by Dr. Hayden 
to the heavy conglomerates and sandstones displayed at Echo Cation and 
other points in the neighborhood of the Wahsatch. 


In regard to assumption number one, there is no doubt that Dr. Hay- 
den is correct. The Fox Hill and Laramie are always strictly conformable 
As regards assumption number two, it must be said that there is con- 
siderable obscurity as to what molluscan species are strictly fresh-water, 


352 SYSTEMATIC GEOLOGY. 


what are brackish-water, and what are truly marine. However this may 
be, the occurrence of beds of Ostrea throughout the whole series up to the 
very summit indicates the access of salt water at all times to the sedimented 
region, and while it may be admitted in general that the fauna might all 
belong to estuarial or littoral regions, at the same time (and this is a point 
upon which I wish to insist) there is no general fresh-water fauna, such as 
characterizes the immediately succeeding group. While east of Colorado 
Range, as we have seen, coal-beds did not make their appearance in the 
series until at the very close of the Fox Hill group, they occurred, as I have 
already shown, at intervals from the very base of the Cretaceous over the 
region adjoining the Wahsatch, and indeed throughout the Green River 
Basin. In other words, the whole enormous thickness of 12,000 feet in the 
Green River region was subject to repeated subsidence, having land-sur- 
faces stretching gradually farther and farther eastward until, at and after 
the close of the Fox Hill period, there were intervals of land-surfaces from 
the Wahsatch far east of the Rocky Mountains into the province of the 
Plains. It is obvious, therefore, that the subsidence was greater in the west, 
and directly proportionate to the superior thickness of the beds in that region. 
Various exposed sections throughout the whole Cretaceous field show that 
the individual coal-beds were of no great geographical extent, and that they 
represented marshy basins, often detached from one another, rarely occupy- 
ing any very great range of country. Yet over the whole area repeated 
subsidence permitted the ocean waters to flow back to the base of the Wah- 
satch. Up to the close of the Fox Hill, it is evident that the subsidences 
were at rarer intervals, or the land remained above the water for smaller 
intervals of time, recording its more rapid subsidence in the more thorough 
sway of the ocean, and consequent predominance of marine life. This state 
of things obtained until the close of the Fox Hill, after which the subsi- 
dences were more frequent and of less vertical depth, and the accession of 
the ocean was more and more retarded. However, through the shallow 
sounds and broad lagoons and estuaries the salt waters still found their way 
back to the Wahsatch, and the general character of the molluscan fauna 
is that of a sound region or of a brackish estuarial type. 

A complete refutation of assumption three, that the fauna proves a Ter- 


RECAPITULATION OF MESOZOIC. 353 


tiary, not a Cretaceous age, is found in the fact that the evidence of a meagre 
molluscan life and a large range of plants cannot be held to weigh against 
the actual presence of Dinosauria in the very uppermost Laramie beds, and, 
as will appear in the sequel, of an abundant lowest Hocene mammalian fauna 
in the unconformably overlying Vermilion Creek group. 

In regard to assumption number four, let it be admitted that the facies 
of the flora bears a noteworthy resemblance to that of the Eocene and Mio- 
cene of Europe, a correlation which I am not prepared to criticise. 

Assumption number five, as to the conformity of the Laramie with the 
Wahsatch group, I shall presently proceed to show, is based upon imperfect 
knowledge, and is abundantly disproved by repeated sections. 

In regard to the sixth assumption, concerning the Fort Union group, 
never having visited that locality, I cannot speak with any definiteness ; 
but I consider it worth while to point out here a noticeable ambiguity in 
its evidence. Cope, in the introduction to his volume on the Cretaceous, 
cites Dinosaurians as coming from Fort Union, from which he refers the 
fauna to the Mesozoic series. On the other hand, the characteristic plant- 
life of the country differs entirely from that described by Lesquereux in 
Volume VII, Tertiary Flora. It is noticeable that. he nowhere describes 
in that volume any of the plants from the classic Fort Union locality, a 
series which has been studied by Newberry, and which contains not only 
a general resemblance, but some actual species identical with the Miocene 
flora of Greenland and northern Europe. It is mentioned by Meek that the 
flora of Miocene facies from Fort Union come from higher beds than the 
Dinosaurians, while the correlation of the Dinosaurian beds, which occur far 
down at Fort Union, with the Black Butte Laramie horizons, as made by 
Cope, seems undoubtedly warranted. The further correlation of the wpper 
plant-beds of Fort Union with the Wahsatch (my Vermilion Creek) seems 
the most prodigious strain. The Wahsatch (Vermilion Creek), or unmistak- 
able lowest Eocene is noneconformable with the Laramie. The relations of 
conformity or nonconformity between the plant-bearing beds of Fort Union 
and the Dinosaurian beds are not given, and there is reason to believe that 
the plant-beds represent a horizon of the great White River Miocene series 
which underlies the Pliocene over so large a part of the Great Plains. Until 

23 K 


354 SYSTEMATIC GEOLOGY. 


fresh evidence of the stratigraphical relations, and a full discussion of the fauna 
of the whole series of rocks at Fort Union is fully made, a definite correla- 
tion is impossible; and at present writing the entire difference between the 
plants at Fort Union and anything in Colorado or Wyoming that is of value 
at all, suggests that they cannot be related to any of the southern groups. I 
apprehend that the plant horizon at Fort Union will be found to be nothing 
but the northward extension of the White River Miocene. 

As to assumption number seven, the term ‘“ Wahsatch” was orig- 
inally applied by Dr. Hayden, as I have before said, to the group of 
conglomerates and sandstones displayed in Echo Canon, and in the Nar- 
rows and at other points in the immediate neighborhood of the Wah- 
satch. In attempting to follow his nomenclature in this region I have 
been led to reject this name, and to apply to those rocks the name “Ver- 
milion Creek group,” because upon Vermilion Creek was exposed the whole 
thickness of the series, while at the Wahsatch the full volume of the 
group was never seen. It consists of a series of conformable beds of sand- 
stones, conglomerates, and clays, having a total thickness of about 5,000 
feet. It appears where Hayden gave it the name of Wahsatch; also, be- 
tween Washakie and Black Butte stations, and over a wide area of the 
Green River depression. Its organic remains are exclusively either fresh- 
water lacustrine mollusks and fishes or abundant mammals. This series will 
be fully described in the following chapter upon the Tertiary age, and its 
relation to the preceding Laramie Cretaceous and succeeding Tertiary 
groups will be treated in detail. For the purposes of the present discus- 
sion, the question of conformity is of the first importance. At the classic 
locality which has served to fix a very grave error, namely, at Black Butte 
Station, the uppermost Laramie beds are found containing mollusks, which 
have already been mentioned, the numerous plant-remains described by 
Lesquereux and referred by him to the lower Miocene, and, besides these, 
the unmistakable Dinosaurian described by Cope. Overlying the Dino- 
saurian bed is a distinct stratum carrying oysters; and-passing up quite con- 
formably, the brackish forms and the Dinosauria disappear together, giving 
place to the fresh-water lacustrine mollusks of the Wahsatch group. There 


is no angular nonconformit~ at this locality, and this single fact is always 


RECAPITULATION OF MESOZOIC. 359 


appealed to as proof of the uninterrupted passage of the Laramie beds, with 
their brackish forms, upward into a conformable series, carrying distinetly 
fresh-water mollusks, and no longer bearing any trace of brackish-water 
organisms. Were this locality the sole exposure of the contact-relations of 
the uppermost Laramie Cretaceous and Vermilion Creek Tertiaries, the 
assumption of their conformability would rest upon solid ground; but, on 
the other hand, in numerous localities along the flanks of the Uinta, upon 
Oyster Ridge in the Green River Basin, and all along the flanks of the 
Wahsatch, it is evident from abundant exposures that the relation of con- 
formity at Black Butte is a solitary exceptional instance, and that every- 
where else the two series are in absolute angular nonconformity, amounting 
in some instances to a full right-angle. It is clearly seen that the Vermilion 
Creck Tertiary overlaps not only the whole Cretaceous series, with which 
it has been alleged to be in conformity, but the entire Paleozoic series also. 
An examination of Geological Map IT. and the eastern half of Map HT. of our 
Atlas shows the relation of these two series in an unmistakable manner. 
They exhibit as a whole one of the most striking, one of the most distinct, 
and one of the most extensive nonconformities which can be observed any- 
where in the Cordilleran system, second only to that which divides the 
Palwozoic from the Archean. Let it be remembered that it is held by 
Hayden and Lesquereux that the uppermost Laramie members are lower 
Miocene. 

Turning now to the Vermilion Creek group, a body of 5,000 feet of 
strata, which I assert to be, with the sole exception in the Fortieth Parallel 
area of the Black Butte region, distinctly nonconformable, what are the 
characteristics of the organic life entombed in the Vermilion Creek series? 
It consists, first, of a remarkable abundance of uncharacteristic fresh-water 
mollusks. But besides that, in beds very near its base, certainly down 
4,400 feet in the series, have been found, as will appear under my descrip- 
tion of the Eocene, an extended vertebrate fauna readily to be correlated 
with a horizon recognized in England and on the Continent as characteristic 
of the lowest Eocene. We have, then, over the Miocene of Hayden a non- 
conformable body of 5,000 feet, all of whose vertebrate remains refer it to 


the lowest Eocene; and I may add, as the reader will perceive in the 


356 SYSTEMATIC GEOLOGY. 


succeeding chapter, that this 5,000 feet of lowest Eocene is overlaid by 
4,000 feet more of middle or upper Eocene, whose abundant vertebrate 
remains are of unmistakable Eocene type. 

To this discussion, therefore, I add the statement of the absolute non- 
conformity of the Vermilion Creek with the Laramie. I fix the beds in 
which the lowest Eocene mammals occur abundantly, near the bottom of 
the Vermilion Creek group. We have, therefore, a brackish group closing 
the Laramie, referred by Hayden and Lesquereux to the Miocene, but which 
carries Dinosaurian reptiles thoroughly characteristic of the Mesozoic age, 
and this is followed by a period of immense disturbance and with complete 
nonconformity, by a subsequent group of purely fresh-water rocks distinctly 
lower Eocene. It will be seen that the stratigraphical break, with its 
unmistakable Eocene facies at the base of the one group, and the Dinosau- 
rian reptile at the close of the other, marks the limits of the period of non- 
conformity as distinctly at the close of the Cretaceous. 

In order to accept the theory of Hayden, the entire Vermilion Creek 
series, the overlying Green River series, and the still overlying Bridger 
series—in all 10,000 feet of Eocene rocks—must be explainedaway. Like- 
wise, the evidence of the Dinosaurian must be ignored. Let it be remem- 
bered that until the close of the Cretaceous, the country from the Wahsatch 
eastward to the Mississippi Basin had been subject to the constant incur- 
sions of the ocean; that all its beds, with the exception of the Laramie, 
were marine; and that the Laramie itself is never distinctly fresh-water. 
What, then, would have caused a profound fresh-water lake, in which 10,000 
feet of Eocene strata could be deposited? It was nothing more or less than 
the great orographical disturbance at the end of the Cretaceous which acted 
over the whole country between the Wahsatch and the Mississippi region, 
causing the sea to retire altogether from the interior of America, abso- 
lutely obliterating the mediterranean ocean which had divided the eastern 
and western land-masses of America since the close of the Carboniferous. 
Not only is the Vermilion Creek series thoroughly nonconformable with the 
Laramie, but without the orographical movement at the close of the Lara- 
mie there would have been no interior basin isolated from the sea, in which 


the lacustrine sediment of the Vermilion Creek group could gather. 


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RECAPITULATION OF MESOZOIC. BLOT 


Finally, the Laramie, by its own vertebrate remains, is proved to be 
unmistakably Cretaceous, and the last deposit of that age, and it contains 
no exclusively fresh-water life. Its plants resemble European Tertiary, but 
its Dinosaurs are conclusive of Cretaceous age. It was the last of the con- 
formable marine deposits of middle America. Its latest period of sedimenta- 
tion was immediately followed by an energetic orographic disturbance, 
which closed the Mesozoic age. In that orographic action the inter-Amer- 
ican ocean was obliterated, and the Cretaceous locally thrown into great 
steep folds. The following deposits over the Green River area were fresh- 
water lacustrine lowest Eocene strata laid down nonconformably with the 
Cretaceous, except in accidental localities. This lowest Eocene has its age 
abundantly proved by vertebrate life, as will appear in the succeeding 
chapter. 


CHAPTER YV. 
CENOZOIC. 


Section I.—EocENE TERTIARY.—VERMILION OREEK GRouPp—GREEN RIVER 
Grourp—BrRIDGER Group—UINTA GROUP. 

Section Il.—M1ocENE TERTIARY.—WHITE RIVER Group—TRUCKEE GROUP. 

Srorion IfL.—-PLIOcENE TERTIARY.—NIOBRARA Group—NortTH Park GRoUP— 
HumMBoLpt GRouP—WYOMING CONGLOMERATE. 

SEcTION LV.—RECAPITULATION OF TERTIARY LAKES. 

SECTION V.—QUATERNARY.—GENERAL REMARKS— EXTINCT GLACIERS AND CANONS 
—DLAKES OF THE GLACIAL AGE AND THEIR DESICCATION. 


SHC TLON L- 
EOCENE TERTIARY. 


In the region of the Fortieth Parallel the changes of configuration 
brought about by orographical movements at the close of the Cretaceous 
period, resulted in the complete extinction of the American mediterranean 
sea, which, since the close of the Coal Measure age, had stretched from the 
Wahsatch to the longitude of eastern Kansas, dividing the east and west 
areas of American land into two distinct bodies. In Eocene time, so far as 
we now know, the entire continental area had a free drainage to the sea, 
with the exception of a long, basin-like depression extending from Wah- 
satch Range eastward to the meridian of 107° 30’, with a north-and-south 
extension not yet definitely known. This depression was immediately occu- 
pied by an early Eocene lake, whose northern portion corresponded with 
approximate accuracy to the present drainage-basin of Green River. South- 


309 


360 SYSTEMATIC GEOLOGY. 


ward it extended through portions of Utah, New Mexico, Colorado, and 
probably into Arizona. 

The series of marine Eocene deposits of the Alabama period are placed in 
a higher horizon than the beds of the Vermilion Creek group, which were 
the first to be laid down in the interior lake. On the western coast, in the 
California region, the uppermost members of the ocean Cretaceous are con- 
formably overlaid by other marine deposits, of which certain members are 
unmistakably Miocene. For the lower members, those directly contiguous 
to the Cretaceous summit, the organic remains thus far collected are too 
indistinet to lead to a firm belief as to their exact age. There are indica- 
tions of Eocene in the series overlying the Cretaceous of Oregon and Wash- 
ington Territory. West of the Sierra Nevada, all the series are purely 
marine, and those of the Alabama and Vicksburg groups, also marine, 
are the only Eocene found east of Colorado Range. 

As yet the great Eocene lake, whose main deposits are circumscribed 
by the boundaries of the basin of Colorado River, is the only one of any 
considerable geographical area known in the middle Cordillera region. In 
its earlier stages this lake was coextensive with the rocks of the Vermilion 
Creek period, the lowest division of the American lacustrine Eocene. 

The great Eocene formation of this region is divided into four promi- 
nent groups: 

1. Vermilion Creek Group, 5,000 feet thick, lowest Eocene. 

2. Green River Group, 2,000 feet thick, middle Eocene. 

3. Bridger Group, 2,500 feet thick, upper Eocene. 

4. Uinta Group, 500? feet thick, latest Eocene, approaching Miocene. 

VeERMILION CREEK Groupr.—Between the uppermost members of the 
Laramie Cretaceous and the lower beds of the Vermilion Creek Eocene, 
there is but very slight lithological difference. They are both reddish, 
friable, sandy rocks. 

After the post-Cretaceous uplift had raised the Rocky Mountain bar- 
rier to the east, forming the basin of Colorado River, the original bottom of 
the newly formed lake was made of the uppermost Laramie beds, of which 
limited portions were left horizontal. When these exceptional localities 
were subsequently covered by Eocene strata, and the two uplifted together, 


EBOCENE TERTIARY. 361 


they were, so far as angle of position is concerned, conformable. But a 
total break of organic life is observable between them; and as stated at the 
close of the Cretaceous section, there is elsewhere a true general noncon- 
formity between the Laramie and Vermilion Creek groups, amounting in 
some places to an angle of 90°. 

Along the eastern limit of the outcrop of the Eocene its beds lie upon 
nearly horizontal Laramie rocks. The line of demarkation, in the frequent 
absence of fossils, is always more or less indefinite, and in consequence 
there may be to the east of our eastern boundary of the Vermilion Creek 
certain outliers in the general Laramie area which truly belong to the 
Vermilion Creek; but since we are unable to determine these, we have 
given a generalized boundary-line. The rocks colored Laramie may be 
relied on as chiefly of that age, the same being true of the Vermilion Creek 
group. This doubt only applies to the horizontal region along the railroad 
and a few miles north and south. 

The most eastern outcrops recognized by us are in a bay-like recess 
between Mount Weltha and Navesink Peak, in the Elk Head region. The 
surface is here composed of coarse red sandstones, interbedded with more or 
less clays and arenaceous marls of pinkish and creamy colors. Tracing this 
formation westward, although the surface is in considerable measure made 
up of decomposed earthy material, yet its character is such as to leave little 
doubt that the subjacent strata are continuous with the more solid Vermilion 
Creek beds which are seen to the west. They present little or no difference 
of angle with the underlying Cretaceous strata at this locality. 

Along the banks of Little Snake River the series is better displayed, 
and is seen to consist of coarse gritty sandstones, containing numerous 
siliceous casts of Melania. There is the same want of definition between 
the Laramie and Vermilion Creek beds, from the junction of Little Muddy 
and Snake rivers northward quite to the Pacific Railroad. 

In the region of the Washakie and Red Desert, and northward as far 
as the boundary of our map, the country consists of a deposit of more or 
less decomposed Vermilion Creek strata. Where they retain their original 
structure, they are seen to be nearly horizontal, and to consist of very easily 
eroded red clay and sandy beds. 


302 SYSTEMATIC GEOLOGY. 


From a little west of Rawlings Peak, the Vermilion Creek beds 
occupy the surface westward nearly to Bitter Creek Ridge, the country 
characterized by irregular barren plains, devoid of the dry water-courses 
which are features of the region to the south. From the Rawlings Peak 
uplift, the Laramie Cretaceous strata were described as falling off with 
rapidly decreasing dip, reaching an almost horizontal position north of the 
railway, between Washakie and Creston. They pass with no uncon- 
formity of dip under the eastern edge of the Vermilion Creek series. 

There is no doubt that in former times the Eocene beds extended con- 
siderably farther to the east, though it seems improbable that they ever 
passed over into the valley of the North Platte, certainly not into the 
depression of Laramie Plain. The exact boundary of the lake, there- 
fore, in which this lowest Eocene group was laid down cannot be given 
along the east in the northern portion of our work. 

South of the parallel of 45°, however, the Cretaceous rocks have a 
higher dip, and a nonconformity with the overlying Vermilion Creek is 
clearly seen. Furthermore, in passing eastward the Green River over- 
laps the Vermilion Creek, and itself comes in contact with the Cretaceous, 
thus clearly proving that the boundary of the Vermilion Lake was in the 
neighborhood of Fortification Peak. About six miles east of Washakie 
Station, Laramie beds are undoubtedly reached, and are recognized in out- 
crops of a thin bed of sandy argillites of a strong vermilion hue. They are 
fine-grained and remarkably fissile, splitting into exceedingly thin laminz, 
which are covered with well preserved impressions of deciduous leaves, 
and are underlaid by the sandstone carrying coal-seams. Ten miles north- 
west of this spot they may be again observed, capped by thinly bedded 
sandstones. In both cases their position is approximately horizontal, the 
slight observable dip being to the west. This red leaf-bed, characteristic of 
the upper region of the Laramie series, serves as a basis for the Cretaceous 
upper limit as colored upon the map. 

About sixteen miles southwest of Washakie, in the near vicinity of 
well recognized Laramie beds, in a rather shallow valley, are beds of 
greenish marls and clays, weathering in the peculiar manner of the Bad 
Lands, developing smooth, rounded, dome-like forms. Their dip of 5° 


EOCENE TERTIARY. 363 


westward would carry them under the Vermilion Creek beds at Cathedral 
Bluffs. A little south of this a discrepancy of angle appears between 
these soft clayey beds and the sandstones of the Laramie, which here rise 
at an angle of 15° to 20°, dipping northwest and striking northeast. East 
of Muddy Creek the bases of the Vermilion Creek benches are made up of 
loosely aggregated sandstones of chocolate, buff, and gray colors, carrying 
Goniobasis and Viviparus in a yellow sand-bed, which appears to represent 
the base of the series in this region. On the western borders of Muddy 
Creek Valley, however, upon the upper edge of the high plateau, are very 
distinct and characteristic outcrops of the bright pinkish and reddish mix- 
ture of sands, clays, and marls which form the upper part of the Vermilion 
Creek series. Their planes of stratification are to be traced by changes of 
color rather than by abrupt changes of material, or those distinctly marked 
surfaces which characterize temporary cessation of sedimentation. 'The 
faces of these bluffs have a peculiar striped, banded appearance, given 
by local variations of green, white, and almost brick-red colors, alternating 
through the general pink mass. Wherever these beds are worn away, the 
sandy particles are most easily transported, and there is invariably a 
residuum of red clay, which gives the peculiar color to the soil of the 
country. The best exposures of these upper striped beds are at Washakie 
Mountain and Cathedral Blufis. The former is a flat-topped ridge, lying 
about seven miles east of Little Muddy River, and reaching an elevation of 
1,500 feet above the surrounding plain, the surface being composed of a 
remnant of the Pliocene conglomerate, afterward to be described. 
Washakie Peak affords an admirable point of view for studying the 
relations of the three different groups of Eocene. A broad expanse is opened 
westward, of 75 or 100 miles. The Green River series which directly 
underlies the Pliocene summit of the mountains is seen to describe a rude 
circle of bluffs having a general dip toward the middle of the Washakie 
Basin. The line of contact between the Green River and the Vermilion 
Creek trends a little west of north from Washakie Mountain to Cathedral 
Bluffs, thence westwardly to Table Rock near Bitter Creek Station, thence 
southwest to Pine Bluffs, and from there southeast to the Vermilion Blufts ; 
and upon the southeast the line is approximately that of Little Snake River. 


364 SYSTEMATIC GEOLOGY. 


Outside of this line, which represents the outer boundary of the Green River 
formation in this basin, are the broad undulating plains of the older Ver- 
milion Creek Eocene, everywhere dipping under the Green River series. 

The middle of this Washakie Basin, as shown upon the map, is occupied 
by a small area, about sixteen by twenty-four miles, of the next higher 
member, the Bridger group. With the exception of the rocks in the region 
of Cherokee Ridge, there has been no considerable plication since the depo- 
sition of these series. The slight dip toward the middle of the basin marks 
the result of orographic action, and cannot be accounted for from dips of 
deposition toward the deepest point of the lake. 

Washakie Mountain itself has a special geological interest, as the upper 
beds of the Vermilion Creek are here seen to underlie the Green River series, 
with a distinct nonconformity of 4° or 5°. The importance of this observa- 
tion will be seen later. 

Between Washakie Mountain and Barrel Springs, and indeed on as far as 
Cathedral Bluffs, the division-plane between the Vermilion Creek and the 
overlying Green River beds may be easily traced by the differences of color 
and texture of the series. This plane of division is depressed in passing 
northward as far as Barrel Springs, and again rises as far as Cathedral 
Bluffs. The whole plain from Washakie Station to Black Butte Station 
is characterized by earthy deposits resulting from the decomposition of the 
Vermilion Creek beds, as usual of prevailing red color from the fine Ver- 
milion Creek clays, which have given the local name of Red Desert to these 
plains. 

A few miles west of Washakie are some low bluffs extending toward 
Red Desert Station, showing some outcrops about the middle of the Ver- 
milion Creek series. They are thin, reddish, flaggy sandstones about 
200 feet thick, underlaid by whitish clays, and have yielded some frag- 
ments of Eocene mammals, of genera which will be found in the list 
appended to the account of this group. South of Red Desert Station, 
the country gradually rises in broad terraces, the first formed of whitish 
clays overlaid by sand-rocks, the outcrops being traced nearly parallel 
to the line of the railway. About four miles south of this chain of bluffs is 
a line of still greater elevations, composed of striped pink, white, and red 


EOCENE TERTIARY. 365 


upper members of the Vermilion Creek. To this line has been given the 
name of Cathedral Bluffs, owing to the remarkable architectural forms 
which have been developed by erosion in the soft, casily wrought material. 
On the northern fronts of these bluffs are exposed about 600 feet of the 
variegated upper Vermilion beds, overlaid by drab limestones which mark 
the base of the Green River series. The summit, member of the limestones 
is a seam about four inches thick of odlites, chiefly silicified, and resulting 
in a dark-gray chert or chalcedony-like material. The plane of junction 
between these two Eocene groups is also shown along an irregular line 
between Cathedral Bluffs and Table Rock, the latter being made up of 
sandstones and caleareous shales, with slight seams of lignite and several 
thin beds of a limestone which is characteristic of the base of the Green River 
series. These limestone beds are almost entirely made up of Melania, Vivi- - 
parus, and Unio, together with the agatized odlitic bed before mentioned. 
The beds here, as usual, dip inwardly toward the centre of the basin in a 
southeasterly direction, at an angle of 4° or 5°. The main body of the 
Vermilion Creek beds at the north dips only 2$° to 3°. 

From Table Rock westward and in the region of Black Butte, is a 
low, open country made up of the disintegrated Vermilion Creek beds, 
in which appear a few outcrops of the still coherent members of the 
group. Along the line of contact with the Green River shales, southward 
as far as Pine Bluffs and even to the old Cherokee Trail, the upper striped 
part of the Vermilion Creek series is conspicuous. The lower members, as 
seen at Black Butte, Hallville, and on the upper part of South Bitter Creek, 
rest with apparent conformity wpon the Laramie Cretaceous, and are only 
to be distinguished by the change in vertebrate fossils. As is the case 
between the lower members of the Vermilion Creek and the Laramie, on 
the east edge of the Washakie Basin the lithological changes are such as to 
render any stratigraphical division valueless. It is therefore true of both sides 
of the Washakie hollow, that the Eocene is practically conformable with the 
Upper Cretaceous. At various points there is a slight appearance of non- 
conformity by erosion, but this is necessarily somewhat deceptive, and the 
line is only to be drawn here with real security upon the basis of vertebrate 
remains which will be mentioned hereafter 


366 SYSTEMATIC GEOLOGY. 


The upper portion of the Vermilion Creek series is observable near Otter 
Gap on Little Snake River, east of Cherokee Ridge. Here the interstratified 
red sandstones and clays give their characteristic color to the country, which 
for the most part is made up of the débris of these beds. Between Otter and 
Elk gaps, the river follows pretty nearly the plane of junction of the Vermil- 
ion Creek and Green River groups. In the region of Sunny Point, however, 
erosion has carried off the Green River series from the immediate hills 
bordering upon the stream, and there are extensive exposures of the upper 
part of the Vermilion Creek, of the characteristic color, and, as usual, much 
disintegrated. The exposure amounts to about 1,000 feet in thickness, and 
is altogether made up of the reddish-colored part of the series. The contact 
between the uppermost of these beds and the calcareous lower horizon of 
the Green River is characteristically observed. The structure in the region 
of Elk Gap is quite complicated, the underlying ‘series considered to rep- 
resent the upper portion of the Vermilion Creek dipping 10° to the south 
and being overlaid by a series of the sandstones carrying at their base a 
prominent bed of reddish shales which dips 29° to the southwest. The 
overlying series are referred to the Green River, but it seems possible that 
they may represent the Bridger, which is seen directly to the northwest. 

East of the river at Godiva Ridge the top of the Vermilion Creek 
series is well shown by its contact with the characteristic cherty Gonio- 
basis bed at the base of the Green River series. 

Around the whole circle formed by the great Green River body in 
Washakie Basin, the upper limit of the Vermilion Creek, as we have seen, 
is quite a defined plane, the variegated and banded red series of the upper 
Vermilion Creek giving way quite suddenly to the calcareous basal mem- 
bers of the Green River series, which are often conformable, but in one or 
two places show distinct nonconformity with the lower series. The broad 
plains which surround the Green River exposure offer few satisfactory out- 
crops and no valuable sections of the lower portion of the Vermilion Creek 
group. Wherever it approaches the nearly conformable underlying Lara- 
mie, the Cretaceous and Eocene possess great petrological similarity. 

The deeper members are better shown in the basin of Vermilion Creek, 


the locality which has given its name to the group. The upper members 


EOCENE TERTIARY. 367 


also are here well shown along the line from Pine Bluffs to Cherokee Trail, 
and again as forming the lower portion of the Vermilion Bluffs, which 
bound the basin upon the southeast. Here, as at Washakie Mountain, the 
uppermost edge of the bluff is formed of unstratified Pliocene conglomerate, 
below which is a development of 500 or 600 feet of the calcareous Green 
River series, underlaid by 800 feet of the characteristic Red-beds of the 
upper Vermilion, which pass downward in the region of Vermilion Creek 
into gray and drab beds. It is the horizon of these gray and drab basal 
members, which are elsewhere rich in bones of Coryphodon. At the foot of 
Vermilion Bluffs the dip is only about 2°, but toward Vermilion Creek it 
gradually reaches an inclination of 12°. 

The whole surface of the basin of Vermilion Creek is a region of terrace- 
like benches, scored and more or less deeply eroded by water-courses, which 
are now for the most part dry. Throughout the lower part of the basin, 
especially near the contact with the underlying and nonconformable Lara- 
mie Cretaceous, are a series of dark-drab and gray gravelly sandstones, 
which lie approximately horizontal, rising very gently to the east and north. 
The underlying Laramie Cretaceous dips to the northeast about 25°, the 
two being utterly unconformable. Attention is especially called to the fact 
of an angular nonconformity of 25° between the Laramie and the lowest 
member of the Eocene, the same groups already noted as conformable at 
Black Butte and east of Washakie. If the geologists who have asserted the 
conformable passage from the Cretaceous to the Tertiary by a transition 
series had not confined their observations in the Green River Basin to the 
region of Bitter Creek and Washakie Basin, the present unreasonable con- 
troversy would never have arisen. The higher members of the Vermilion 
series, as exposed on the western flanks of Vermilion Creek valley, are 
coarse gravelly sandstones, the upper portion of which has the character- 
istic red color of the formation. Directly north of Diamond Mountain these 
higher Vermilion Creek beds yielded several bird-bones from a coarse, 
gritty, buff sandstone. Passing southward, the uppermost members of the 
group come into nonconformable contact with the Carboniferous limestones. 
Southeast of Diamond Peak, and along Talamantes Creek, the whole series 


are seen to pass unconformably over the Cretaceous, Jura, Trias, Permian, 


368 SYSTEMATIC GEOLOGY. 


and upper Carboniferous, coming finally into contact with the Weber quartz- 
ite of O-wi-yu-kuts Plateau. 

The meridian of Bishop’s Mountain, a little northeast of Diamond Peak, 
marks an anticlinal in the Vermilion Creek series. Eastward the whole 
strata incline gently to the east, to pass under the Green River and Bridger 
series of the Washakie Basin, and westward beneath the Green River rocks 
of Tabor Plateau and Quien Hornet Mountain. The entire thickness of the 
Vermilion Creek series, as displayed in the basin of Vermilion Creek, cannot 


be less than 4,000 feet. 
Considered as a whole, the Tertiary field lying east of the meridian of 


Quien Hornet Mountain is a single broad basin, of which the Vermilion 
Creek forms the lowest member, and upon the east and north lies conform- 
ably as to its angle upon the Laramie beds of the Cretaceous, while to the 
south the discrepancy of angle between those two formations amounts to 
25° at Vermilion Creek, and to 3° or 4° near Fortification Peak, in the val- 
ley of the Yampa. The greater part of the area is covered by easily eroded 
earthy beds of the Vermilion Creek series, which are characterized by the 
presence of a considerable number of fresh-water Tertiary genera — 
Melania, Goniobasis, Viviparus, and Unio, and also by the bones of verte- 
brates, including Coryphodon. 

The upper limit is frequently well marked by contact with the lower 
limy members of the Green River series; but since these two members are 
nonconformable, the Green River often overlaps and obscures the edges of 
the Vermilion Creek beds. This is the case between Sunny Point and Ver- 
milion Bluffs, and also through the whole Tertiary exposure from Godiva 
Ridge to the White River divide. West of the meridian of Bishop’s Moun- 
tain the Vermilion Creek beds incline very gently to the west, passing be- 
neath the irregularly eroded Green River series. 

Along the immediate base of the Uinta Mountains the later strata are 
eroded off, leaving a narrow strip of the Vermilion Creek beds extending 
from the head of Willow Creek westward to the slopes of Mount Corson. 
Along this line is an admirable opportunity of studying the relations of 
the Vermilion Creek with the Cretaceous. West of the ford of Green River, 
about four miles north of Flaming Gorge, the upper Cretaceous sandstones 


EOCENE TERTIARY. 369 


of the Laramie group are seen dipping to the north at very high angles, 
25° near the river and increasing westward, until at the gap where Henry’s 
Fork enters the Quaternary valley north of Camp Stevenson the Laramie 
sandstones dip 75° or 80° to the north, while the Vermilion Creek beds, 
distinctly and nonconformably above them, dip only 25°. Continuing still 
farther west from the gap north of Dead Man’s Springs, the Vermilion Creek 
beds swing to the south and overlap first the Fox Hill, then the Colorado, 
and later the Dakota. They are in turn overlaid by the unconformable 
Bridger series, forming with a Pliocene gravel-cap the mass of Mount Cor- 
son. The lowest Vermilion Creek member exposed along Henry’s Fork is 
a coarse conglomerate which underlies some striped red sandstones, the 
conglomerates dipping 25° to 35° northward. 

Along the western side of the Bitter Creek uplift and in the valley of 
Sage Creek the erosion of the calcareous beds of the Green River series 
has laid bare a narrow belt of the Vermilion Creek lying between the 
Green River group and the Laramie Cretaceous. The relation with the 
Laramie sandstones is obscure, owing to the soft and friable nature of both 
series. 

North of Uinta Range, to the east and west of where Bear River 
emerges from the mountains, the foot-hills are deeply overlaid with Ter- 
tiary sandstones and conglomerates, which, near the mouth of Bear River, 
have a dip of 8° or 10° from the range. Extending westward along the 
flank, these conglomerates become more and more important, until directly 
north of the upper cation of Weber River the mountain wall is composed 
of excessively coarse conglomerate between 3,000 and 4,000 feet thick. 
It is almost structureless, and lines of stratification can rarely be perceived. 
The blocks of which the conglomerate is chiefly formed range from the 
size of a pea to masses with a weight of several tons. Here and there a 
comparatively fine-grained bed gives a clew to the dip, and the formation is 
seen to incline from 4° to 5° northward away from the foot-hills of the range. 
The rapidity with which these conglomerates grow finer in advancing from 
the shore along the Uinta is very conspicuous. Of these coarse conglom- 
erates, perhaps the most remarkable exposure is on a point directly north 


of the upper Weber Cation, about ten miles south of the 41st parallel. 
24 Kk 


370 SYSTEMATIC GEOLOGY. 


This peak is over 11,000 feet high, and marks the greatest altitude which 
the comparatively undisturbed Tertiaries have been observed to attain. 
To the north the ridge and peak are scored down by deep canons which 
well display the graduation of the material from the coarse conglomerate 
immediately in contact with the older rocks out toward the north, until, 
near Wahsatch and Evanston, they have become fine-grained, sandy beds, 
devoid of pebbles. A section displayed on the 111th meridian, from the 
high peak to Evanston, estimating from the observed dips, indicates a thick- 
ness of about 4,000 feet of strata; while from Evanston to Croydon, on the 
Union Pacific Railroad, some distance to the west, certainly 2,000 feet of 
lower beds are displayed. It is entirely within bounds to assign to the 
Vermilion Creek of this region a total thickness of 5,000 or 5,500 feet, and 
it should be borne in mind that this nowhere represents the former summit 
of the Vermilion Creek series. On the contrary, we can but suppose that 
a considerable portion of the uppermost beds have been removed, and 
hence that an unknown amount is to be added to the total thickness of the 
group. 

In the region of Aspen Plateau the Vermilion Creek beds are about 
horizontal, and are, for the most part, alternately of cream-colored and 
red arenaceous clays, with not infrequently a considerable proportion of 
marly strata. They have yielded in this vicinity numerous fragments of 
Coryphodon, which add certainty to the assignment of the rocks of this 
region that had been already made upon structural and stratigraphical 
grounds. East of Aspen, both the Vermilion Creek group and the small ex- 
posure of Green River group pass rapidly under the unconformable Bridger 
beds, and the eastern flank of Aspen Plateau seems to have been the western 
limit of deposition of the Bridger beds of the Bridger Basin. 

At the mouth of Echo Canon the Vermilion Creek conglomerates are 
seen to contain a large number of rounded pebbles, from extremely fine 
sizes up to six, eight, and even ten inches in diameter. The latter size, 
however, is very rare. Passing up in the series, the conglomerate beds 
are capped by Indian-red sandstones, which expose in Echo Canon fine 
precipitous fronts, carved down by transverse ravines, which carry off the 
drainage from the high Tertiary plateau to the north. Between Echo City 


EOCENE TERTIARY. 301 


and the top of this plateau are represented about 3,800 feet of strata, chiefly 
of these Indian-red sandstones, containing toward the upper limit gray 
shale-beds, with occasional sheets of fine conglomerate. 

Directly west of Coalville the Vermilion Creek rocks are seen to rest 
unconformably upon the northwesterly dipping Cretaceous. This line of 
discordant contact may be traced southwestward across Weber River, appear- 
ing on the hill-sides north of Silver Creek. From Echo City along this 
entire line of contact, even past the north side of Parley’s Park, there is no 
single instance in which any close observer could possibly assume a con- 
formity between the Vermilion Creek beds and the underlying Cretaceous. 
On East Cation Creek the discrepancy rises to 50° or 60°, gradually growing 
less toward Echo City, until directly south of the mouth of Echo Canon 
the nonconformity is reduced to about 10°. At Croydon low beds of Ver- 
milion Creek are seen resting unconformably upon the Fox Hill sandstones 
of the Cretaceous, the latter dipping 25°, while the Tertiaries never dip 
over 5°, and are for the most part nearly horizontal. 

East of the great Cambrian anticlinal of the northern end of the 
Wahsatch, shown on Map IIL, is a parallel highland, the Bear River 
Plateau. It is merely an area of elevation that has escaped the extreme 
erosion which the beds in immediate contact with the Cambrian and Silu- 
rian rocks of the older uplift have suffered. It varies from two to five 
miles in width, and on the east overlooks the valley of Bear River and 
descends by a series of rudely sloping spurs, which are separated by the 
canons of Woodruff, Randolph, and Saleratus creeks. The beds here are 
inclined from 1° to 2° to the east, and show a thickness of about 2,500 
feet. They have the usual characteristic red color, and are made up of 
prevailingly coarse arenaceous materials, with occasional strata carrying suf- 
ficient pebbles to be denominated a loose conglomerate. ‘There are a few 
beds of nearly pure, white, fine, siliceous sand, which are striped with fine 
seams of gray argillaceous marl. On the divide between Saleratus and 
Lost creeks the coarseness of the material increases westward till it shows a 
perceptible approach to the heavy conglomerates displayed in the Narrows 
below Croydon and at Echo City. The western edge of Bear River Plateau 
descends by a rapid declivity, often almost an escarpment, between 2,000 


312 SYSTEMATIC GEOLOGY. 


and 3,000 feet deep to the level of the Silurian and Cambrian rocks. This 
abrupt, precipitous face is cut by deep canons, the branches of Blacksmith’s 
Fork and Muddy River. These canons do not cease their cutting action 
when they reach the harder rocks of the Silurian and Cambrian beds, but 
have deeply scored through that anticlinal, making gorges 1,800 to 2,000 
feet deep in the quartzite. From the peculiar relations of the topography 
of the Bear River Plateau with the older rocks, it is clear that the Vermilion 
Creek rocks formerly passed uninterruptedly over the summit of the older 
anticlinal, that the courses of the streams were determined in the softer Ter- 
tiary above, and that upon cutting down to the level of the harder under- 
lying rock they were confined by the Tertiary walls above and obliged to 
erode in the thus predetermined channel. Afterward, long after the streams 
had cut deeply into the older rocks, the Tertiaries were in great measure 
removed. 

On the western side of Oyster Ridge and west of Concrete Plateau 
there is an enormous development of red sandstones and clays, with promi- 
nent belts of conglomerate, the whole increasing in coarseness of sediment 
as it approaches the Uinta on the south and the Wahsatch on the west. 
Here is an area about sixty miles from north to south by fifty miles from 
east to west, which is essentially a plateau of Vermilion Creek beds, in 
general approximately horizontal, but in the vicinity of the Wahsatch rising 
to 14°. On the south it abuts without change of angle against the Uinta 
Mountains, and between Upper Bear and Weber rivers forms an elevated 
plateau which reaches 11,000 feet, a plateau made up of coarse, irreg- 
ular strata of red gritty conglomerate material, dipping northward at 
angles of 3° to 4°. On the flanks of the Uinta, canons have been carved 
out of these loose, friable strata by the ice action of the glacial period, 
leaving sharp, deep walls 1,000 to 1,200 feet in height. 

Between Weber River and Wahsatch Range there is a lofty plateau 
culminating in an extremely high point, which reaches nearly 11,000 feet. 
This plateau is cut through by the valley of East Canon Creek, and not 
less than 4,500 or 5,000 feet of horizontal sandy and conglomerate beds of 
the Vermilion Creek group are displayed. They are here nearly horizon- 
tal, but toward Richville, farther down on East Canon Creek, the red sand- 


EOCENE TERTIARY. ale 


stones of the group are seen dipping from the Wahsatch at an angle of 
about 14°. The railway crosses a point of this plateau through a sharp 
gorge at the Narrows, where the Tertiary conglomerates and sandstones 
are nearly horizontal and about 2,000 feet thick. 

In the region of Bear River City and Evanston, the Cretaceous, which 
stands nearly vertical, has its highest members dipping at an angle of 70°. 
Here, as at Black Butte, the uppermost beds lying above the heavy white 
sandstones of the Laramie consist of a variety of thin, sandy shales, having 
many carbonaceous beds, more or less clays, and thin streaks of coal, the 
whole carrying enormous numbers of Unio, Corbicula, Corbula, Pyrgulifera, 
Viviparus, Melampus, &c.; and here the rocks of the Vermilion Creek series 
are horizontal—in other words, there is an angular discrepancy of 70°. 
They are characterized by the presence of Melania and Goniobasis, and also 
by numerous mammalian remains of the typical Eocene genus Coryphodon. 

At Evanston the highest portions of the Laramie Cretaceous are not 
exposed, but the sandstones near the summit of the group contain the 
enormous workable coal-beds of the Rocky Mountain and Wyoming Coal 
companies. These coal-bearing Laramie beds dip at angles from 16° to 
25°, whereas the Vermilion Creek Tertiaries are nearly horizontal over 
them, and carry remains of the genera Coryphodon and Eohippus, and fishes. 

In the region of Echo Canon, again, the uppermost members of the 
Laramie are not displayed, but the distinctive Vermilion Creek beds, which 
have been traced in absolute continuity from the Coryphodon beds near 
Evanston, are here seen to overlie unconformably the Cretaceous, the angu- 
lar discrepancy being 12° to 25°. Near the upper part of the cation, below 
Castle Rock, they reach their greatest nonconformity in that immediate 
region, and near Echo City there is a difference of 11°. The continuous 
series of Vermilion Creek beds, passing westward, overlaps all the Palzeozoic 
formations, which are conformable with the Cretaceous, and comes directly 
into contact with the Archzean. 

Between Bear River and Oyster Ridge is a further extension of this 
great Vermilion Creek Plateau, abutting nearly horizontally against the 
highly inclined Cretaceous of the ridge. The broad upper valley of 
Bear River is excavated from these strata, which occupy the heights to the 


374 SYSTEMATIC GEOLOGY. 


west, and extend thence across Bear River Plateau. Along the eastern side 
of the Wahsatch, east of Farmington and Keysville—indeed, from Hunts- 
ville all the way to Parley’s Park—the Vermilion Creek beds rise high upon 
the flanks of the Wahsatch, the highest portions of the Tertiary being fre- 
quently higher than the top of the older range. ‘This is true of the whole 
Bear River Plateau, and true of the Vermilion Creek heights directly north 
of Parley’s Park. The only exposure of these beds west of the summit ot 
the Wahsatch is to be found in a small body of hills lying directly north 
of Salt Lake City, of which Ensign Peak is a prominent point. This is a 
mass of sandstone and conglomerate, which has been faulted down into 
its present position. ‘The entire absence of this great series to the west 
of the Wahsatch would indicate that the range itself formed approximately 
the shore of the lake, and it is probable that the small detached mass around 
Ensign Peak was merely a bay of the Tertiary putting into the land which 
lay to the west. 

From the outcrops thus broadly sketched, it is clear that a single lake 
extended from longitude 106° 30’ to 112°, stretching northward probably 
over the greater part of the Green River Basin and southward to an unknown 
distance. The rocks of this same group which occur in New Mexico 
represent a southern continuance of the identical lake, characterized by 
the same fauna. So far as the area of the Fortieth Parallel goes, these rocks 
have only been definitely studied in the region east of the Wahsatch and 
north of the Uinta. South of the latter range, from the heights west of 
Strawberry Valley eastward across Green River, extends a broad area of 
Tertiary rocks of great thickness. These have not been sufficiently studied 
to say definitely to what members of the Eocene they belong. In the region 
of White River some beds have yielded fossils which, although Eocene, 
have a more recent facies than those of the highest or Bridger member to 
the north of the Uinta. They are still lower than the Titanotherium beds 
which form the base of the Miocene east of the Rocky Mountains. It 
seems most probable that the immense mass of Tertiary south of the west- 
ern end of the Uinta, which is shown in the valleys of Du Chesne, Red 
Fork, and upper Uinta rivers belongs to the Vermilion Creek series. In 
the absence of more definite information, the whole sweep of the Ter- 


EOCENE TERTIARY. By 65) 


tiaries south of the Uinta, with the exception of certain little patches of 
known Pliocene, has been colored as the Uinta group, whose upper mem- 
bers near White River have yielded the highest Eocene forms; but there 
is no doubt whatever that subsequent study will show that the rocks in 
the angle between the Uinta and the Wahsatch south of the former range 
are identical with those in the opposite angle north of the Uinta, and that 
they should be classed with the Vermilion Creek. And the altitudes to 
which the level Tertiary strata northeast of Strawberry Valley attain, indicate 
that the level of their deposition was as high as the rocks north of the 
Uinta. We may expect a full elucidation of the Tertiaries south of the 
Uinta from the pens of Powell and Gilbert. 

The thickest exposures of the Vermilion Creek series are in the imme- 
diate vicinity of the Wahsatch, as shown by the deep valley of East Canon 
Creek, where is exposed not less than 4,000 feet. The most characteristic 
exhibition is in the basin of Vermilion Creek, where a fuller section is dis- 
played. It is made up of a heavy, gritty series at the base, which in the 
region of Vermilion Creek and north of Evanston is gray, but as displayed 
at Echo Canon and East Cation Creek is characterized by the presence of 
enough red sandstones and clays to give it more of a brick or in places a 
deep pinkish color. The middle members are of finer material and are more 
intercalated with clays, while the upper part of the series, as shown wher- 
ever the group comes in contact with the Green River series, is made up 
of striped and banded sandstones varying from gray to yellow, white, and 
red, with prevailing red and white tints. 

As regards the relations of this with the underlying group, it should be 
repeated that the evidence has finally accumulated so that there can be no 
longer a doubt where to draw the line between the Cretaceous and the Ter- 
tiary series. I unhesitatingly say that the bottom of the Vermilion Creek 
is the base of the Tertiary, and that it rests in essential nonconformity 
(though locally in accidental conformity) upon the Cretaceous. 

The Cretaceous members, as we have seen, are inter se strictly con- 
formable. The uppermost exposures in the near vicinity of the Vermilion 
Creek beds are along the Bitter Creek uplift, at Evanston, at the eastern 
end of the O-wi-yu-kuts Plateau, Red Creek, the northern slopes of the 


376 SYSTEMATIC GEOLOGY. 


Uinta, Oyster Ridge, Bear River City, and Echo Canon. Of all these 
localities, the only one where there is the slightest appearance of conformity 
of position is in Washakie Basin, where the inclinations of the two forma- 
tions are practically identical, and the appearance of nonconformity by 
erosion is wanting. The Cretaceous, as we have seen, is here characterized 
lithologically by a variation between beds of heavy sandstone, yellowish 
shales, finely laminated sandstones, dark clayey shales, ashy, laminated 
clays, and numerous intercalated beds of coal. The organic remains of 
these upper Cretaceous, as I have shown when describing that formation, 
are numerous vegetable remains, including the leaves of palms, and mol- 
lusks of the genera Ostrea, Anomia, Corbicula, Corbula, Cyrena, Goniobasis, 
and Viviparus; while above these Meek, Bannister, and Cope exhumed a 
portion of a skeleton of Agathawnus sylvestris, a distinctly Cretaceous Dino- 
saur. Passing upward, Cope obtained in the immediately overlying series 
the following list: 

Clastes ? glaber. 

Emys megaulax. 

Emys pachylomus. 

Emys euthnetus. 

Trionyx scutumantiquun. 

Alligator heterodon. 

Orohippus vasacciensis. 


All these types are distinctly Tertiary. The following list, partly 
from Green River Basin, will give the characteristic features of the verte- 


_brate fauna of the group: 
VERMILION CREEK GROUP, 


CARNIVORA. 
Oxycena lupina, Cope. 
Oxyena forcipata, Cope. 
Pachyena ossifraga, Cope. 
UNGULATA. 
Phenacodus primevus, Cope. 
Meniscotherium chamense, Cope. 
Helaletes singularis, (Cope) Marsh. 


EOCENE TERTIARY. Sidad. 


Enohippus tapirinus, (Cope) Marsh. 
Lohippus angustidens, (Cope) Marsh. 
Eohippus cuspidatus, (Cope) Marsh. 
Eohippus validus, Marsh. 
Eohippus major, Marsh. 
Eohippus pernix, Marsh. 
Parahyus vagans, Marsh. 
Coryphodon hamatus, Marsh. 
Coryphodon elephantopus, (Cope) Marsh. 
Coryphodon latidens, (Cope) Marsh. 
Coryphodon radians, (Cope) Marsh. 

TILLODONTIA. 
Dryptodon crassus, Marsh. 
Esthonya bisulcatus, Cope. 
Ectoganus gliriformis, Cope. 
Calamodon simplex, Cope. 

REPTILIA. 

Diplocynodus stenops, Cope. 
Crocodilus grypus, Cope. 
Crocodilus heterodon, Cope. 
Trionyx leptomitus, Cope. 
Trionyx radulus, Cope. 
Plastomenus corrugatus, Cope. 
Plastomenus communis, Cope. 
Dermatemys costilatus, Cope. 


It will be seen from these facts that I am fully justified, first, in assert- 
ing general nonconformity between the Laramie and the Vermilion Creek; 
secondly, that the angular conformity in the region of Washakie Basin is 
exceptional; thirdly, that the Vermilion Creek fauna is distinctly lowest 
Eocene. 


Green River Grovp.—Not only is the middle member of the Eocene 
series, or the Green River group, unconformable with the rocks of the Ver- 


milion Creek group, but from certain occurrences in western Utah and 


378 SYSTEMATIC GEOLOGY. 


eastern Nevada it is now known that it overlaps to the westward at least 
200 miles. Within the area covered by Vermilion Creek rocks the Green 
River series rests for the most part unconformably upon the horizontal as 
well as the highly inclined Vermilion Creek beds. It probably somewhat 
overlapped the Vermilion Creek rocks toward the east, but the area of 
the lake in which it was deposited expanded westward to certainly twice 
the east-and-west dimensions of the lake of the Vermilion Creek period. 

At first it seemed possible that the exposures of the Green River Eocene, 
which are observed in western Utah and eastern Nevada from longitude 
114° to 116°, might represent a second middle Eocene lake, whose deposits 
and fauna are identical with the contemporaneous deposits and fauna in 
the Green River region; but the recent discovery of Tertiary beds near 
Stockton, west of the Oquirrh Mountains, and the extension from the Oyster 
Ridge region far to the northwest, or toward the Great Basin country, con- 
firm the general belief that the detached outcrops between the meridians 
114° and 116° are really parts of the sediments of one lake. 

The way in which the Vermilion Creek beds abut against the eastern 
flank of the Wahsatch nearly up to its summit, is sufficient warrant for the 
belief that that range formed the westward barrier for a great amount of the 
sediments of the early Eocene lake. But when we pass eastward from the 
immediate neighborhood of Wahsatch Range, it is found that the slightly 
inclined Vermilion Creek beds rise rapidly in altitude, still maintaining their 
horizontal position and forming extensive plateaus, which have been more 
or less eroded, leaving isolated highlands and even mountain peaks, all made 
of horizontal beds. Such points are the high peak directly northwest of 
Wanship, and the elevated plateau country north of Croydon, also Bear 
River Plateau, which lies to the east of the Cambrian anticlinal on the 
northern portion of our Map III. From an examination of the outcropping 
edges of these horizontal Vermilion Creek beds, it is clear that if continued 
westward they would pass over the top of Wahsatch Range; while an ex- 
amination of the country to the west of the range shows a depressed basin 
in which, so far, no traces of Vermilion Creek rocks have been discovered. 
One must therefore believe either that the Vermilion Creek rocks formerly 


extended over the top of the now exhumed Wahsatch Range and continued 


EOCENE TERTIARY. 379 


to some indefinite distance westward, or else that the Wahsatch formed the 
barrier to the westward extent of the lake, and that subsequent faults have 
carried down the region west of the range, while the erosion of the glacial 
period has degraded the main Wahsatch range, so that it is now below the 
level of the Eocene plateaus directly to the east. From evidence to be 
adduced in the chapter which treats of orographical disturbances, it will 
be seen that unquestionably a series of enormous faults occurred posterior 
to the deposition of the Vermilion Creek series, which depressed the whole 
country out as far as middle Nevada, and which permitted the waters of 
the Eocene lake to flow westward and make a comparatively continuous 
sheet from the Rawlings uplift at longitude 107° to longitude 116°. Ac- 
companying this great dislocation, the Vermilion Creek rocks east of the 
Wahsatch were thrown into a series of more or less abrupt folds. Along 
the northern slope of the Uinta, in the region of Henry’s Fork, they were 
uplifted at an angle of 25°, and in general they sagged downward to form 
two prominent basins, one of which forms the Bridger Basin, the other the 
basin of Washakie. 

At the beginning of its existence, then, the middle Eocene lake had 
for its bottom, from its eastern shore as far west as the Wahsatch, the hori- 
zontal or upturned beds of the Vermilion Creek, that covered all but the 
single mass of Uinta Range, which probably formed a great east-and-west 
island in the lake. That portion of the lake lying west of the Wah- 
satch occupied a region in which the Carboniferous were the uppermost 
rocks, a region which had been a continental land-mass since the 
close of the Carboniferous, and over which no Mesozoic or lowest 
Eocene strata had been deposited. It was, indeed, the land area from which 
the materials of the eastern Mesozoic and the main mass of the Vermilion 
Creek Eocene beds had been furnished; and it must have been, as we may 
judge from the relations of the slight exposures of western Eocene beds to 
the older rocks, a comparatively corrugated region characterized by bold 
ranges of Palseozoie rock, many of which doubtless projected above the 
level of the middle Eocene lake, creating a complex archipelago. 

From the character of the Eocene deposit west of the Wahsatch, we 


may assume that the lake in that region during the latter part of its history 


380° SYSTEMATIC GEOLOGY. 


was comparatively shallow, and that the detritus was largely derived from 
the islands, partaking of their extremely localized character. On the other 
hand, the rocks of the Green River Basin of this same period show deeper 
waters and excessively fine sediments, which might have been transported 
from a considerable distance, and which doubtless represent material not only 
from the neighboring Uinta Range, but from a variety of different sources 
around the whole shore of the lake. The sediments, deposited noncon- 
formably against the sharp, ridgy chains of the archipelago of the west, 
show always a sharp nonconformity with the immediately underlying 
rocks. On the other hand, in the region east of the Wahsatch, a large 
amount of the Vermilion Creek series was left in a nearly horizontal posi- 
tion, and the sediments there sank quietly through deep water upon an 
approximately level bottom, accumulating in strata nearly conformable 
with the underlying Vermilion Creek rocks. From the manner in which 
the rocks of the Green River group abut westward against the Vermilion 
beds, it is evident that there was in the region included between the Wah- 
satch and Uinta a highland lifted above the lake of the Green River period. 

Exactly the extent and area of all the islands which rose above the 
surface of the Green River lake, it is at present impossible to tell. The central 
and higher parts of the Uinta were out of water, but it seems quite clear that 
the depressed portions of the eastern end of the range were for the most part 
submerged. 'The entire Vermilion Creek series, as we have seen, was made 
up of sandstones and intercalated clays, with more or less conglomerates 
near the old shores of the lake. This detritus doubtless came partly from 
the erosion of the siliceous Cretaceous beds which must in great part have 
formed the shore and islands of Vermilion Lake. But it would seem that 
about the close of the Vermilion Creek period, erosion must have worked 
off from the higher summits most of the Mesozoic rocks, and with the 
beginning of the Green River group have begun its work of degradation 
upon the calcareous beds of the Carboniferous. 

The Green River beds are in sharp contrast with those of the earlier 
Eocene, first, by the extreme fineness of the material, and, secondly, by 
their calcareous nature. As a whole, east of Wahsatch this group consists 


of caleareous sands and slightly siliceous limestones, which are overlaid by 


EOCENE TERTIARY. 381 


remarkably fissile calcareous shales, the former abounding in fresh-water 
mollusks, the latter in the remains of fishes, plants, and insects. The lower 
member, the impure limestones, probably reaches about 800 feet in thickness, 
and the thin, fissile, caleareous shales about 1,200 feet, making a total of 
2,000 feet for the entire group. To what height they originally reached 
along the northern flank of the Uinta, is in a great measure unknown. 
Where the overlying Bridger group overlaps them and abuts against the Coal 
Measure limestones of the Uinta, as it does from Mount Corson to Concrete 
Plateau, there is, of course, a certainty that the Green River beds extended 
no farther to the south; and likewise directly west of Concrete Plateau, 
where the Bridger comes into actual contact with the Vermilion Creek, it is 
clear that the Green River beds did not extend in that direction. But in 
the region of the present valley of Green River they doubtless extended 
much higher against the flanks of the range, and east of the Uinta 
saddled across the divide into the valley of White River. Over the 
Washakie Basin they occupied the greater part of the area, and were there 
again deposited as fine calcareous sediments. Detached outliers of the 
Green River series still exist between the Bitter Creek Cretaceous uplift 
and the Archzan mass at the head of Red Creek, sufficient to show that 
the sheet of sediment stretched over all that country and connected the 
Washakie and Bridger basins. 

The chief present outcrops of the Fortieth Parallel region are: First, a 
narrow strip east of Oyster Ridge, first observed near Piedmont Station, 
where it overlies unconformably the Vermilion Creek rocks, and is itself 
overlaid by the Bridger with heavy Quatenary desert deposits to the 
east. This narrow zone extends in a northeasterly direction as far as the 
northern limits of our map, and probably over into the Nevada extension 
of the Green River lake, the exposure gradually widening to the north, 
where it covers eight or ten miles. 

The next, and by far the most characteristic development, is a broad 
belt extending from the northern edge of the map in a meridional direction 
down the valley of Green River to the foot-hills of Uinta Range. It is from 
this typical display in the valley of Green River that the group has derived 
its name. Farther east the broad area occupying the middle of Washakie 


382 SYSTEMATIC GEOLOGY. 


Basin, and extending over the region from O-wi-yu-kuts Plateau to the 
White River divide and southward, forms decidedly the most important geo- 
graphical area of this group within our limits. 

The most eastern exposures are west of the valley of Little Muddy 
Creek, in the region of Washakie Mountain, where the variegated upper 
beds of the Vermilion Creek group, which have a dip of from 4° to 5° 
westward, are overlaid by the horizontal brown sandstone and blue cal- 
careous shales and clays of the Green River series. 

This locality is of special interest as displaying the nonconformity of 
the two groups at the most eastern exposure of the Green River, and the 
gradual rise of the Vermilion Creek group passing eastward would indicate 
that a portion of the earlier group was lifted above the level of the lake of 
the Green River period, or at least above its plane of deposition. From 
this point the margin of the Green River formation defines a rude circle 
through Cathedral Bluffs, Table Rock, Pine Bluffs, Vermilion Bluffs, and 
Sunny Point, the strata of the series always presenting their edges to the 
exterior of the area in a more or less important escarpment, but dipping in 
from every direction, at gentle angles, toward the centre of the basin. In 
passing from Washakie to Cathedral Bluffs the plane of contact of the Ver- 
milion Creek and Green River series is depressed toward the north until at 
Barrel Springs it reaches the lowest point, and then rises again. 

At Cathedral Bluffs, capping an exposure 600 or 700 feet thick of the 
upper Vermilion Creek beds, is a layer 100 or 150 feet thick of the impure 
limestone which forms the base of the Green River group. It is here of 
concretionary structure, with a dull drab color, carrying more or less sili- 
ceous matter, and near the top a prominent seam four or five feet thick of 
odlitic limestone largely metamorphosed into chalcedony. The round grains 
are from a thirtieth to a tenth of an inch in diameter. They are of more 
or less concentric structure, showing a cryptocrystalline calcareous cement. 
They are probably crystallitic and not organic, and may be related to the 
calcareous spherical sands, examples of which are now found on the beaches 
of Great Salt Lake. They here contain 74.81 of silica, the remainder being 
carbonate of lime. Besides this bed there is a prominent chalcedonic 
stratum made up of casts of Goniobasis. Farther west, at Table Rock, 


EOCENE TERTIARY. 383 


the summit is of calcareous beds with more or less lignite, several of the 

thin limestone beds being almost entirely composed of Melania, Viviparus, 
Unio, and other fresh-water shells. The siliceous odlitic bed observed upon 
‘athedral Bluffs recurs here. 

Very characteristic displays of the Green River series are observed at 
Pine Bluffs, a conspicuous escarpment which offers a commanding view over 
the valley of South Bitter Creek and the Washakie and Vermilion Creek 
basins. The upper 400 feet of the escarpment are made up of a highly 
calcareous buff sandstone, which dips 4° to 5° to the east and strikes a little 
east of north. Directly beneath the sandstones are white, shaly beds un- 
derlaid by thin sandstone, all slightly calcareous. 

At the Springs, where Bitter Creek emerges from the Green River area, 
about ten miles north of Pine Bluffs, are admirable exposures of the charac- 
teristic limy beds and shales of remarkably fissile structure, which readily 
split into flakes almost as thin as a sheet of paper. These are more or less 
interspersed with carbonaceous and arenaceous beds, the carbonaceous mem- 
bers especially showing a tendency to whiten on exposure to the air. Con- 
siderable surfaces of the upper valley of Bitter Creek are covered by white 
chips of the calcareous and carbonaceous shales, which, by exposure to the 
air, have acquired this peculiar chalky appearance. The shales at Barrel 
Springs, another point near the extreme boundary of the Green River area, 
lying south and east of Cathedral Bluffs, are highly carbonaceous, and, as 
usual, are intercalated with more or less sandy members. They are rich in 
leaf-impressions, and among the numerous fresh-water mollusks have been 


recognized — 
Unio. 


Tellinides. 

Goniobasis tenera. 
Goniobasis nodulifera. 
Goniobasis Cartert. 


In the region of Cherokee Ridge the very slight dip toward the centre 
of the Washakie Basin, which is observed in all the distinct outcrops of the 
Green River area, gives way to a local anticlinal where beds of the series 
are observed dipping 7° northward, the line of Cherokee Ridge marking 


384 SYSTEMATIC GEOLOGY. 


pretty nearly the axis of the anticlinal. The series here consists of drab 
laminated sandstones, slightly calcareous and abounding in casts of Gonio- 
basis, the sandstones passing into slightly saccharoidal, creamy-brown lime- 
stone. The whole northern half of this anticlinal declines at first to 7°, 
passing unconformably under the overlying Bridger series to the north; 
but the southern member of the anticlinal, which seems to have been some- 
what faulted up, declines to the south at angles of from 25° to 30°, marking 
the highest slope developed in the Green River group. 

The area enclosed between Vermilion Bluffs, Brown’s Park, the Esca- 
lante Hills, and Snake River, is one in which the relations of the Tertiary 
are involved in much obscurity. It is a region which has suffered exten- 
sive faults and extraordinary erosion, and is for the most part largely cov- 
ered with deep accumulations of soil. It is certain that at some point in 
Vermilion Bluffs the Green River strata occupy the surface, and we are 
unable to observe any break from Vermilion Bluffs southeastward into 
Brown’s Park. The rocks in Brown’s Park are also in great measure covered 
by local accumulations of soil. Throughout the southern part of the valley, 
wherever exposed, the Tertiaries are seen to be approximately horizontal, and 
to be composed of soft, friable beds. Along the north wall of the valley there 
is a sharp break, however, and the Tertiary rocks which come to the surface lie 
immediately against the quartzitic sandstones of the plateau and dip to the 
south at an angle of 18° to 25°. They are of a rather coarse, gritty char- 
acter, containing many sheets of fine pebbles, and are prevailingly calca- 
reous. They are unlike any Tertiary in the region; but from their calca- 
reous nature, the fact of their being upturned at so high an angle, and their 
apparent connection with the series which sweeps around the eastern 
end of O-wi-yu-kuts Plateau, they are assigned by Mr. Emmons to the 
Green River age. There seems to be a decided difference between the 
strata which were seen uptilted along the south base of the O-wi-yu-kuts 
Plateau and the soft, white, friable, horizontal beds of the valley itself, which 
are seen to extend eastward well toward the divide separating the valley of 
Vermilion Creek from that of Little Snake River. It is not improbable 
that there are two distinct members here—the Green River, which is seen 
inclined along the northern edge of the park, and a more recent horizontal 


EOCENE TERTIARY. 385 


member, assigned to a special group by Powell, which overlies the beds we 
have referred to the Green River age. 

The surface of the whole Green River outcrop, both of the Washakie 
Basin and of the southern area from Vermilion Bluffs southward to the 
White River divide, is always characterized by a more marly soil, by infre- 
quent outcrops of solid rock, and by the prevalence, among the few actual 
exposures, of calcareous members, sandy shales, or thin fissile shales, vary- 
ingly carbonaceous, and always more or less charged with casts of Gonio- 
basis, Melania, and Viviparus. Along the whole valley of the Little Snake, 
at Sunny Point, as well as at Godiva Ridge and Elk Gap, the lower horizon 
of the Green River group is easily recognized, consisting of calcareous sand- 
stones and impure limestones, resting, as usual, upon the brilliantly striped 
beds of the upper Vermilion Creek. At Sunny Point particularly there is 
a thickness of about 950 feet of Green River, made up as follows: 


Feet. 
1. Coarse brownish sandstone, with intercalated brown calcareous 


SIME 2 oA as See ee ee ne Be eres ee einer aecarte 100 
2. White calcareous shales, with half-inch seams of gypsum and a 


four-inch seam of agatized Unios.-..-.-------------------- 45 
3. Drab, concretionary limestone, with brown sandstone shales.-.. 85 
4. White and brown argillaceous shales...-.-------------------- 120 
beitusty, arenaceous, shales: --_.... 4-2-8. 24----+=------2----- 100 
6. Beds of soft, light-colored, argillaceous and calcareous shales, 

some of which are impregnated with carbonaceous material 

and have a light blue color on the weathered surface, contain- 

ing also small seams of gypsum ..-.----------------------- 400 
fee ibitersandstones;and (clays 2) 5282-6 2252-2 100 


The relation of the two series at Elk Gap is somewhat perplexing, 
from the unusual attitude of the rocks. The lower exposure consists of the 
upper members of the Vermilion Creek group, which dip to the south at an 
angle of 10°, but are overlaid by a series of somewhat calcareous sand- 
stone having at the base a prominent red shale, the upper member dipping 
29° to the southwest. A short distance down the river both series are 
found perfectly conformable. In order to account for this position, it is 


25 K 


386 SYSTEMATIC GEOLOGY. 


necessary to suppose that, prior to the deposition of the Green River 
series, a portion of the Vermilion Creek series was faulted up with a 
considerable northerly dip, and that since the deposition of the Vermilion 
Creek series nonconformably over this faulted rock, a second disturbance 
has taken place in this locality which has reversed the dips of both series to 
south, thus bringing the underlying bed, which formerly had a steeper dip 
to the north, into the position of a less steep dip to the south. It is notice- 
able that the line of strike of this steeply southward-dipping Green River 
series at Elk Gap would carry it directly into the northern edge of Brown’s 
Park, where beds also assigned by us to the Green River series hold the 
same position, dipping 25° to the south. It would seem, therefore, that a 
long line of displacement has occurred here, with a downthrow to the 
south. Provided the upturned beds in Brown’s Park are, as we suppose, 
Green River, there is a vertical displacement of 5,000 feet between them 
and the series of the same horizon north of the Archean mass on Red Creek, 
the Brown’s Park being the depressed member. 

Around the base of Godiva Ridge, overlying the variegated beds of the 
Vermilion Creek series, are the sandy and calcareous lower members of the 
Green River series, capped by white limy rocks, containing silicified beds 
made up of casts of Goniobasis, an occurrence, as we have seen, most fre- 
quent in the lower Green River series. There is apparently a slight non- 
conformity between the two series here, but it is decidedly less marked 
than at Elk Gap. 

Beneath the Wyoming conglomerate on the summit of Vermilion 
Bluffs is an exposure of 500 or 600 feet of calcareous beds, here largely 
made up of papery shales of the Green River. 

Excellent exposures are obtained on Vermilion Creek, below its canon, 
which is cut through the Carboniferous series. Here the beds are com- 
posed of a characteristie white, fine-grained, siliceous material, intercalated 
with coarser, loosely compacted drab sandstones, the latter containing 
among the siliceous material a great many feldspar and mica particles. 
Besides these intercalations, certain members of the white silts have a pecu- 
liar silky lustre, and pass into fine siliceous limestones and calcareous shales. 
Moreover, not a few of the limestone beds develop concretionary structure, 


EOCENE TERTIARY. 387 


a peculiarity confined, so far as we have seen, among all the Tertiaries, to 
the Green River group. 

The White River divide, as before mentioned, is formed of the Lara- 
mie Cretaceous rocks, which have a sharp northerly pitch of 25°. They 
are unconformably overlaid by soft calcareous Tertiaries which dip to the 
north at only 3°, and which stretch uninterruptedly northward, connecting 
with the caleareous beds of Godiva Ridge. As displayed near the divide, 
there are about 1,500 feet of these rocks, which are unquestionably but 
the relic of a wider extension. From the character of the Green River 
series directly south of the White River divide, where their identification is 
rendered complete’ by the recurrence of fossils characteristic of the beds in 
the region of Green River City, there is no doubt that the Green River beds 
formerly saddled across the whole divide and formed a continuous sheet of 
sediment far to the south. 

Beneath the Wyoming conglomerate of Bishop Mountain a thin sheet 
of the Green River calcareous beds extends to the north and west toward 
Tabor Plateau, overlying the upper beds of the Vermilion Creek series. 
On the western side of South Bitter Creek, upon Tabor Plateau, and 
thence for fifteen or twenty miles northward, the Green River series 
not only overlies the Vermilion Creek, but overlaps the Laramie and Fox 
Hill Cretaceous beds, the calcareous Eocene beds having a dip of 4° 
to the north. 

From twelve miles above Green River City down to Flaming Gorge, 
the whole valley of Green River is excavated from the nearly horizontal 
strata of the Green River series. Between the Cretaceous of the Bitter 
Creek uplift and the eastward margin of the area of the Green River rocks 
is a narrow band of the Vermilion Creek rocks, extending from north of the 
map as far as Sage Creek. Between this series and the Cretaceous rocks, 
we have described a slight nonconformity ; but between them and the 
overlying Green River calcareous beds just to the west there seems to be 
no recognizable angular discrepancy, at least as far south as Sage Creek. 
From that point southward there is a slight and growing discrepancy, 
which, north of the northern foot-hills of the Uinta, becomes a perfectly 
distinct nonconformity. North of Big Horn Ridge, and especially where 


388 SYSTEMATIC GEOLOGY. 


Green River enters the Quaternary valley north of Camp Stevenson, the 
discrepancy between the two series is also perfectly clear. 

Perhaps the most characteristic development of the Green River series 
is to be found in the neighborhood of Green River City, where the Union 
Pacific Railroad crosses the river. Here, on both sides of the stream, the 
broad valley is walled in by cliffs and hills formed of the calcareous shales 
and sandstones of the Green River group, which are displayed for a thick- 
ness of scarcely less than 2,000 feet. Inarailway-cut on the western bank, 
the extremely fine paper shales that occur on both sides of the river have 
yielded numerous fossil fishes, of which the more characteristic forms are 
enumerated later in the section. 

Plate XIV. gives an excellent idea of the steep cliff bordering the river 
immediately north of Green River City. Here the shales are excessively 
thin and fine-grained. Plate XIII. is a close, detailed view of the same 
cliff front. 

The plateau north of the railway and east of Green River Valley is 
a gently rolling summit. In the immediate vicinity of the railway, rise 
isolated, tower-like rocks, which possess all the abruptness and hardness of 
outline of artificial fortifications. The sculpture of the shales along the 
river banks is also extremely interesting, displaying vertical cuts 300 or 
400 feet high, capped by rounded hill-tops, and these in turn by towers. 
South of the city, on the eastern side of the river, is a remarkable series 
of hills stretching back four or five miles from the river, appropriately 
called by Powell the Alcove Ridges, from their singular mode of erosion. 
The river cliffs are here cut by transverse ravines, bold headlands project- 
ing against the river bank with almost vertical faces. The exceedingly 
fine characteristic shaly structure of the upper part of the group is also 
well shown in Bitter Creek Valley, in a railway cut The plateau to 
the north of the railway presents to the south and east a bluff from 
800 to 1,000 feet high. All these strata dip at gentle, almost imper- 
ceptible angles to the west toward a middle line of depression, in the 
Bridger Basin. At a short distance west of Green River the calcareous 
shales pass, with apparently a slight unconformity, beneath the softer beds 
of the overlying group. As exposed by the river-cut and the Aleove Ridges, 


LOCENE TERTIARY. 389 


there is no less than 2,000 feet of the series displayed, of which the white 
and brown paper shales occupy the upper 1,200 feet. Throughout this 
thickness they are more or less intercalated with arenaceous beds, which at 
the base of the shale-series rapidly increase in proportion and become more 
and more calcareous, finally appearing either as marly sandstones or as 
creamy-white, brittle, fine grained, earthy limestones. Capping the shales, 
and making the uppermost member of the series in the region of Green 
River, are displayed about 100 feet of brown-sandstone of massive structure. 
It forms the heavy, dark-brown cap upon the bluffs in the region of Green 
River City, where all traces of the original stratification are lost, and the 
rock presents an appearance of somewhat peculiar local metamorphism. 
The physical characteristics, especially the compactness, of this upper rock, 
vary very greatly, and to this fact may be due the circumstance, that ex- 
ceptional parts of the bed have resisted erosion and protected the softer 
underlying shales from wearing down, which has resulted in the remarkable 
turret and bastion forms that characterize the region. 

Although enormous numbers of individual fossil fishes are obtained 
from these shales, the number of genera is exceedingly small. The types 
are closely allied to those of Monte Bolea, in Italy. Fresh-water mollusks 
which are found in the more compact limestones of the lower portion of 
the group are chiefly Viviparus and Goniobasis, genera found in both the 
Vermilion Creek and the overlying Bridger series. There are no brackish- 
water forms whatever. A considerable amount of the fine calcareous shale- 
series is heavily charged with bituminous matter, a very large portion of 
which is volatile. 

Throughout the region near the railway the shales possess a charac- 
teristic dip of 3° to 4° to the west, which they retain on the western side 
of the river. Near the summit of the low, flat ridge between Green 
River and Black’s Fork, they pass under the thinly bedded drab sandstone 
which forms the base of the Bridger group. The latter never possesses a 
dip of more than 2°. The contact of these rocks is well covered with 
disintegrated soil; but when last seen the Green River beds, before they 
pass under the Bridger, still retain their dip of 4°. It is therefore probable 


that the two formations have here a slight nonconformity, a condition 


390 SYSTEMATIC GEOLOGY. 


of things which is rendered more probable by the peculiar overlap of the 
Bridger in the region of Concrete Plateau. 

The dip of 4° extends all the way down the river to the lower valley 
of Henry’s Fork. East of the river this group forms broad terraces which 
ascend toward the east as far as the meridian of Quien Hornet Mountain, 
while a short distance to the west of the river they invariably pass under 
the horizontal Bridger series. With the exception of the anticlinal in the 
Green River group, already described at Cherokee Ridge, the highest 
observed dips of this series are along the flanks of the Uinta Mountains. 

From Quien Hornet Mountain to Green River the caleareous under- 
lying members of the group dip at 5° to the north, with a slight inclination 
to the west, unconformably overlying the Vermilion Creek group with a 
discrepancy of angle of 5° to 12°. 

Where Green River emerges from its upper valley into the broad, open 
area above its confluence with Henry's Fork, the limestones which form 
the base of the Green River series dip 5° to the north, while the underlying 
sandstones and clayey beds of the upper portion of the Vermilion Creek 
underlie them at higher angles, usually 8° to 14°. West of Green River 
the upper shales appear at the bases of the long eastern spurs. From Twin 
Buttes, and north of Dead Man’s Springs, the valley of Henry’s Fork 
passes through the Green River formation for four or five miles. Here: is 
displayed a small lignite bed. The highest inclination recognized in these 
beds is north of Dead Man’s Springs, where the low ridges, made up of 
yellow sandstone and the creamy-colored brittle limestone, dip northward 
from 20° to 25°, carrying, as usual, an infinite number of casts of Gonio- 
basis. 

West of Bridger Basin the display of Green River rocks is very 
limited. As before mentioned, it at first makes its appearance coming out 
from under the Bridger beds in the vicinity of Piedmont, and thence 
northward its exposure increases in width, until at the northeastern 
edge of our map the belt is about thirty-five miles wide, and probably 
includes the northern limit of the Bridger Basin. South of Piedmont it 
seems clear that the Bridger group completely overlaps the Green Tiver, 
coming directly in contact with the Vermilion Creek, which gradually 


y 
g! 


4 


ay 


EOCENE TERTIARY. 391 


rises toward the west, occupying higher and higher positions, till it reaches 
the elevated plateau made in the angle between Uinta and Wahsatch ranges. 
This plateau, which received its relative elevation at the close of the Ver- 
milion Creek period, slopes gradually to the east and again gradually to 
the north, and the Green River formation abuts against the gently inclined 
beds of this series, describing a curve northward, and swinging around to 
the west through northern Utah into Nevada. Near Piedmont the white, 
impure limestones and thin, calcareous shales have yielded a few fishes 
sdentical with those found in the shales near Green River City. North- 
ward they pass across the railway west of Carter’s Station, and are there 
represented by light, creamy, calcareous beds. 

Down the valley of Bear River, beyond the northern limits of Map 
IIL, the rocks of the Green River group have been observed by Dr. 
Hayden, and north of Oyster Ridge, on Fontanelle Creek, by Professor 
Cope. The discovery of this group at these two points seems very clearly 
to warrant the belief that the lake of that period extended westward around 
the north of Bear River Plateau, connecting with the deposits to the west, 
which are about to be described. . 

At the extreme northwestern limits of the Great Salt Lake Desert, 
at the eastern foot of the prominent group of the Ombe Mountains, out- 
crops a series of beds which dip at an angle of 45° to the east, with a 
general north-and-south strike. Their most prominent exposures are about 
ten miles south of the railway. Although devoid of fossils, they are 
readily referred by their lithological characteristics to the Green River 
series, consisting as they do of white and thinly bedded shales, both 
siliceous and calcareous, equally fissile with those of Green River, and, 
like them, charged with richly bituminous zones, the latter sometimes 
reaching the condition of coal and appearing in beds one or two feet in 
thickness. The material of the coal is a jet black, lustrous mass, which, 
however, slakes, crumbles, and becomes valueless on exposure to the air. 
This correlation is not based solely on the resemblance of the beds to those 
of the distant Green River Basin, but also on identical rocks a little farther 
west, which are well charged with Green River group fossils. 


A few miles farther west, and a short distance from Peoquop Range, 


392 SYSTEMATIC GEOLOGY. 


there is a break in the continuity of the great Paleozoic bodies. In this 
depressed basin, as shown on Map IV., where the Quaternary is not pres- 
ent, may be seen the upturned edges of rocks of the Green River period, 
striking about east-and-west, resting unconformably upon the Palzeozoic 
series on both sides of the gap. They strike a little north of east, and dip 
both to the north and south, with a varying inclination of from 5° to 20°. 
They are in general a series of fine carbonaceous shales and marls of a pre- 
vailing yellow-brown hue, though occasionally passing into blackish beds, 
where the carbonaceous matter is highly concentrated. The lowest strata 
are heavy red shales and marls, with a few indurated gray clays as the 
basal member. Although no organic remains have been found here, they 
are referred to the Green River period by their exact resemblance to the 
beds which occur at Elko, a little farther west. 

A further development of these Green River beds is found in Hunting- 
ton Valley, extending from Dixie Valley southward. The rocks occur 
here as a low ridge between the Dixie trachyte hills upon the west and a 
body of Lower Coal Measure limestones on the east. They consist of 
creamy calcareous rocks, sandy marls, and fine calcareous shales, con- 
taining the usual carbonaceous seams, and even thin coal-beds. The eal- 
careous shales yield fragments of fossil fishes evidently identical with those 
of Elko, but too nearly obliterated for specific determination. The beds 
have a dip of 30° to the east, and strike about north 20° east. Here is 
displayed an interesting relation to the trachytes which have broken through 
them. 

A very characteristic member of these Green River shales is found 
on the eastern base of the River Range, due north of the station of Osino. 
As in the Dixie group, the characteristic beds are white and creamy 
brittle limestone, in beds six inches to a foot thick, overlaid by calcareous 
and arenaceous shales carrying beds of clay from one to two feet thick. 
The development of carbonaceous material here rises to the importance of 
coal-beds, of which one is two feet, another five to six feet, another three 
feet thick, besides which there are many brown beds of carbonaceous 
material containing a high proportion of volatile hydrocarbons, burning 


when heated with an intensely bright flame for a short time, and then 


EOCENE TERTIARY. 393 


crumbling into a loose ashy residue. The coals of the true coal-beds are 
black, lustrous lignites, containing a great many yellow, amber-like grains, 
and white coatings of sulphate of lime through the cracks and fissures of 
the coal. Like the Ombe coal, this rapidly slakes and crumbles upon expo- 
sure to the air, and has little commercial value. Above the coal-seams in 
the characteristic bituminous shales, which are here highly calcareous, the 
true paper shales of the formation, are found great numbers of fishes and 
insects of the identical species occurring at Green River City. 

From all that may be seen at Dixie and on the flanks of River Range, 
it is probable that there are 2,500 or 3,000 feet of beds in these exposures. 
At the coal-mine the dip is 45° to the east, while farther down the ravine it 
rises to G5°. The same series of beds recurs in Elko Range, east of Elko 
Station. They here have a strike about due north, and dip 35° to the east, 
and consist of very thin shales, sometimes calcareous, often sandy, and again 
dark-brown, with bituminous matter. Fragments of an undeterminable fish 
were the only fossil discovered by us here. 

West of Dixie Hills no outcrops of the Eocene have been recognized, 
and for the present we must consider that Pinon Range was the western 
boundary of the Green River group. 

I ought not to close this subject without remarking again that, although 
I consider the general tendency of the evidence warrants the belief that 
these western deposits represent truly the extension of the great lake of the 
Green River period, yet at the same time the absence of outcrops between 
Ombe Range and Bear River renders it possible that the western group of 
occurrences may represent an independent lake.* 

Whatever may have been the climate in the region of the western out- 
crops, there can have been no change between there and the Bridger Basin. 
The atmospheric condition must have been practically the same; and since 
both sets of strata are characteristic of still and deep-water deposition, it is 
not strange that the species should be the same, even if the lakes themselves 
had no communication. It is only necessary that they should drain into 


*Since the above was written, inclined coal-bearing fresh-water Tertiaries have been observed 
near Stockton, at the base of Oquirrh Range, thus indicating very positively that the group once stretched 
quite to the base of the Wahsatch. 


394 SYSTEMATIC GEOLOGY. 


the same ocean to account for the identity of species, because the only 
remains of aquatic fauna besides the fresh-water mollusks have been fishes, 
certain of which, from their nature, once probably migrated annually to 
the south and were afterward land-locked. 

The following are some of the more characteristic fossils of this group: 


GREEN RIVER GROUP. 


FISHES. 


Clupea humilis, Leidy. 
Clupea alta, Leidy. 
Clupea pusilla, Cope. 
Osteoglossum encaustum, Cope. 
Asineops squamifrons, Cope. 
Asineops viridensis, Cope. 
Erismatopterus Rickseckeri, Cope. 
Heliobatis radians, Marsh. 
INSECTS. 
Antherophagus priscus, Scudder. 
Endiagogus saxatilis, Scudder. 
Trypodendron impressus, Scudder. 
Corymbites velatus, Scudder. 


Bripcer Grour.—The belt of Eocene country studied by this Explo- 
ration leaves some open questions as to the physical conditions at the close 
of the period of the Green River rocks. I have shown that at the close of 
the Vermilion Creek the lake which had formerly extended from the meri- 
dian of 107° 30’ to the Wahsatch was rather suddenly allowed to expand 
itself westward to the meridian of 116°, the expansion being caused by the 
subsidence of the country between the Wahsatch and the meridian of 117°. 
So isolated are the present outcrops of the Green River rocks which have 
accumulated in the western portion of the lake, that we have a very slender 
basis from which to reason as to its conditions. The fauna was identical 
with that of the Green River Basin, the rocks show a singular likeness to 
those in the eastern areas 

We are somewhat at a loss when we proceed to examine the areas and 


EOCENE TERTIARY. 395 


character of the Bridger group or next succeeding member of the Eocene; the 
main difficulty being to determine whether the few isolated bodies of Bridger 
rocks represent parts of what was formerly a continuous sheet, or whether 
at the close of the Green River period the lake limits were immensely con- 
tracted, and the Bridger series only permitted to accumulate in certain small, 
detached basins. Much light would be thrown on this were we able to decide 
finally whether the Green River and Bridger series are conformable with 
each other; but it so happens that the Bridger beds are usually found 
in the middle of basins, in nearly horizontal position. These areas of 
Bridger rocks are surrounded, as a glance at the map will show, by groups 
of the Green River formation, which pass under the Bridger at angles so 
slight as to leave it somewhat uncertain whether they are strictly uncon- 
formable. On this point, however, all the positive evidence is in favor of a 
true nonconformity. Whatever may have been the conditions in the basin 
of Green River, it is clear that the western part of the lake, namely, that 
west of the Wahsatch, never received any sediments of the Bridger period, 
since it is inconceivable that if they had accumulated in such a large area 
as the expanded Green River period lake is known to have covered, some 
fragments should not have escaped both processes of removal and burial 
which have been active over this area since Eocene times. 

From the relation of the Green River beds with the high, rocky, 
mountainous ridges near the 116th meridian, it is evident that there were 
large areas from which detritus must have been removed during the Bridger 
age, and there is no reason to suppose that very much less material would 
have been accumulated than in the basin of Green River, for nearly uniform 
climatic conditions must have obtained over both regions ; and while 2,000 
feet of the sediment of the Bridger period were accumulating in the restricted 
basin of Green River, there was land-mass enough, which must have 
yielded a very large, if not indeed an equal amount of sediment over 
the area of the western part of the lake. The total absence of any Bridger 
beds may be considered as a strong indication, amounting almost to proof, 
that there was a great physical change at the close of the Green River 
age, which gave to the country west of the Wahsatch, drainage either to 


the sea or into the Green River Basin; in other words, that it was no longer 


396 SYSTEMATIC GEOLOGY. 


a lake west of the Wahsatch. That since the Green River period there 
has been sufficient mechanical disturbance of the area to bring about the 
new condition, is evident from the extreme dips of the Green River rocks 
near the River Range of Nevada, where they reach 60°, and at Cherokee 
Ridge, in Wyoming, where the southern side of the east-and-west anticlinal 
dips to the south at angles reaching 25°. If this disturbance took place, as 
the evidence indicates, immediately at the close of the Green River period, it 
will sufficiently account for the isolation and limitation of the deposits of the 
Bridger period. If, however, they succeeded the Green River beds without 
any orographical changes, we can only account for their absence over the 
region west of the Wahsatch by supposing that the sediments of the Green 
River had previously filled up that portion of the lake. In either case, 
there was no lake during Bridger time west of the Wahsatch. 

Supposing the Bridger beds of the Washakie and Bridger basins. to 
have been deposited conformably in the same lake which laid down the 
Green River series, and to have been uplifted together with the Green River 
in a post-Bridger upheaval, it is not a little remarkable that erosion should 
have removed the Bridger from all parts save the middle of these two 
basins. The few observations which bear upon this point in the way of the 
dips of the two formations combine to indicate that the movement took 
place at the close of the Green River period, that the western lake was extin- 
guished by this upheaval, and that the waters of the period formed a lake of 
restricted area altogether within the basin of Green River. Even with this 
supposition, which I conclude to be the most probable until it may be varied 
by future evidence, there is left the shadow of a doubt whether the three 
Bridger bodies which appear upon our map—that of the Bridger Basin, the 
Washakie Basin, and the region east of Vermilion Creek—were parts of a 
continuous sheet, or whether they themselves were areas of special lakes in 
the same general basin, isolated from each other, but characterized by great 
fauna resemblances. 

A glance at the eastern half of Map II. shows that the middle of the 
Washakie Basin is occupied by an irregular area of beds of the Bridger 
period. It has an extension of about twenty-five miles from east to west, 


by sixteen to twenty from north to south. It is completely surrounded, as 


rs Ae 
Reyes + 


AY 


pe 


1 


-3 


EOCENE TERTIARY. 397 


already described, by the beds of the Green River period, which dip at 
gentle angles toward the middle of the basin. The inclination is never 
over 4°, except on the northern side of the Cherokee anticlinal, where it 
steepens northwestward to 7° and passes with apparent nonconformity under 
the Bridger series. 'The country around the girdle of Green River rocks 
is largely covered with soil, and the few outcrops are either creamy lime- 
stones, calcareous shales, or slightly calcareous sandstones. Immediately in 
the neighborhood of the junction of the Bridger and Green River groups, 
the plains are covered with extensive deposits of soil, so that the actual con- 
tact of the two deposits is rarely seen. 

From twelve to fourteen miles southwest of the head of Bitter Creek 
are seen exposures of the soft green clays, marls, and whitish-gray 
sands of which the upper beds of the Bridger group are made. Pass- 
ing eastward of Pine Blufis, the country is covered with more or less 
drifting sand, which forms noticeable trains of dunes. The sand sud- 
denly gives way to the soft Bridger beds which are intricately eroded into 
branching ravines. This bad-land country extends southeastward to the 
mouth of a dry valley north of Cherokee Ridge, and from that point a 
chain of bluff escarpments extends northeasterly for twelve or four- 
teen miles. The relations of this sharp wall to the Green River coun- 
try to the south are obscured by deep accumulations of valley soil; but 
the nearest approach of the two sets of strata shows the Bridger lying 
nearly or quite horizontal, the other dipping at 7°. 

This escarpment is the most remarkable example of the so-called bad- 
land erosion within the limits of the Fortieth Parallel Exploration. The 
Bridger beds here rise about 300 feet above the level, dry valley to the 
south, and present a series of abrupt, nearly vertical faces, worn into 
innumerable architectural forms, outliers often standing detached from the 
main wall in bold blocks, which have been wrought into a variety of singu- 
lar forms by wolian erosion. Plate XV. gives a very fair general view of 
a portion of the Bad Lands, showing some of the curious buttressed shapes. 
A few ravines eut their way through the plateau from considerable 
distances back in the basin. Along the walls of these ravines the same 
picturesque architectural forms occur, so that a view of the whole front 


398 SYSTEMATIC GEOLOGY. 


of the escarpment, with its salient and reéntrant angles, reminds one of 
the ruins of a fortified city. Enormous masses project from the main wall, 
the stratification-lines of creamy, gray, and green sands and marls are 
traced across their nearly vertical fronts like courses of immense masonry, 
and every face is scored by innumerable narrow, sharp cuts, which are 
worn into the soft material from top to bottom of the cliff, offering narrow 
galleries which give access for a considerable distance into this labyrinth of 
natural fortresses. At a little distance, these sharp incisions seem like the 
spaces between series of pillars, and the whole aspect of the region is that 
of a line of Egyptian structures. Among the most interesting bodies are 
those of the detached outliers, points of spurs, or isolated bills, which are 
mere relics of the beds that formerly covered the whole valley. These 
blocks, often reaching 100 feet in height, rise out of the smooth sur- 
face of a level plain of clay, and are sculptured into the most remarkable 
forms, surmounted by domes and ornamented by many buttresses and 
jutting pinnacles. But perhaps the most astonishing single monument 
here is the isolated column shown in the frontispiece of this volume. It 
stands upon a plain of gray earth, which supports a scant growth of desert 
sage, and rises to a height of fully sixty feet. It could hardly be a more 
perfect specimen of an isolated monumental form if sculptured by the 
hand of man. 

Looking along the perspective of this strange line of escarpments, the 
uniform buff and gray marls and clays are seen to be interrupted at several 
elevations by beds of peculiar green earth, which add to the architectural 
forms the element of variegated courses. Not the least remarkable feature 
is the fact that the plains skirting the base of these Bad Lands are quite 
level, there being little or no talus at the bottom of the abrupt slopes of the 
cliffs. It is easy to see that these exceedingly fine materials, when dis- 
lodged from their original positions in the beds, would be rapidly carried 
away by the waters which are concentrated by the ravines and angles of 
the Bad Lands. The present clay floor at the foot of the cliffs has almost 
the appearance of the accumulation of a lake, but it is in reality only the 
detritus levelled by flowing water, a task which the exceedingly fine nature 
of the material renders comparatively easy, and which is permitted here 


EOCENE TERTIARY. 399 


by the slope of the underlying Green River beds toward the Bad-Land 
escarpment. 

These bluffs are extremely rich in the remains of vertebrate fossils. 
At the base of almost every cliff were observed the bones of Mammalia, 
and frequent shells of Testudinata. 

It is not altogether easy to account for the peculiar character of this 
erosion, resulting as it does in such singular vertical faces and spire-like 
forms. A glance at the front of these Bad Lands shows at once that very 
much of the resultant forms must be the effect of rain and wind storms. 
The small streams which cut down across the escarpment from the interior 
of the plateau do the work of severing the front into detached blocks; but 
the final forms of these blocks themselves are probably in great measure 
given by the effect of rain and zxolian erosion. The material is so exces- 
sively fine that under the influence of trickling waters it cuts down most 
easily in vertical lines. A semi-detached block, separated by two lateral 
ravines, becomes quickly carved into spires and domes, which soon crum- 
ble down to the level of the plain. Outlying hills or buttes are carved 
away, leaving narrow, isolated spires, which finally disappear by the same 
process of erosion. It seems probable that some of the most interesting 
forms are brought out by a slightly harder stratum near the top of the 
cliffs, which acts in a measure as a protector of the softer materials, and 
prevents them from taking the mound-forms that occur when the beds are 
of equal hardness. As to the thickness of the Bridger series in the Wa- 
shakie Basin, no precise figure can be arrived at. It probably amounts to 
less than a thousand feet. 

A little west of south from Washakie Basin, between Vermilion Bluffs 
and Elk Gap, is a detached area of soft, easily eroded clays and sands, 
which, from their position overlying the paper shales of Green River, have 
been assigned to the Bridger. No organic remains were found here, and 
the occurrences are of very slight importance. 

The chief exposure of the Bridger beds is to be found in Bridger Basin, 
between the meridians of 109° 30’ and 110° 45’, extending from the 
foot-hills of the Uinta, on the south, northward beyond the limits of our 
map. As displayed along the base of the Uinta Mountains, it consists of a 


400 SYSTEMATIC GEOLOGY. 


series of soft, sandy, and clayey beds, for the most part covered with 
soil, or obscured beneath unconformable deposits of Pliocene conglom- 
erates, and wherever distinctly seen it is found to dip at gentle angles to the 
north, angles never exceeding 2°, and hence within the probable limit of 
the original deposition. Thus exposed, there is a body of 50 to 60 miles 
from east to west, the main axis trending a little east of the meridian. It 
is bounded on the east, in the region of the meridian of 109° 30’, by the 
shales of the Green River series, which come upon the surface from a posi- 
tion beneath the Bridger. On the west, also, it is margined by a narrow 
line of Green River beds, separating it from the still lower Vermilion 
Creek group. 

Throughout the middle of the Bridger Basin it rests in positions of 
complete horizontality, and throughout its whole extent shows no evi- 
dence of orographical disturbance, such as could be registered in local 
changes of angle. The aggregate thickness of the beds of this group is 
estimated as between 2,200 and 2,500 feet. The material is almost wholly 
made up of fine sand and clay, arranged in varying proportions, and occasion- 
ally slightly changed by calcareous admixtures. 

As between this series, however, and that of the Green River, the 
notable difference is, that the Bridger is a prominent sand-and-clay forma- 
tion, while the other, from bottom to top, is essentially characterized by 
the presence of abundant lime. The strata of the Bridger are also exceed- 
ingly soft, and are eroded with almost the facility of beds of Quaternary 
earth. The upper 1,000 feet are nothing more than a soft, sandy clay sedi- 
ment, varying from drab to pale olive, carrying a few beds of slightly in- 
durated sandstone and occasional stripes of grayish and greenish marls, and 
at one or two horizons beds of inconspicuous limestone, which closely re- 
sembles the arenaceous limes of the Green River group. 

One of the noticeable features of this group is the vitrification of cer- 
tain beds. It is not uncommon to observe, along the steep escarpments of 
the eroded clays and sands, the edge of a hard bed standing out like a shelf, 
which upon examination proves to be chert or hornstone, sometimes inclining 
to semi-transparence, in which case they represent chalcedony, or more 


nearly hyalite. Such sheets are of not infrequent occurrence, but are 


EOCENE TERTIARY. 401 


usually of no great lateral extension. They rarely exceed three or four 
feet in thickness, and but for their lithological peculiarities would be an en- 
tirely unimportant member of the series. There are also calcitic and 
selenitic intercalations, from which erosion removes the superincumbent 
clays, leaving the surface covered with the rubbish of crystals. In the 
siliceous hyalitoid strata, innumerable dendritic infiltrations of iron and 
manganese are observed, whose most highly developed form is the well 
known moss-agate of the region. ' 

On the northern limit of the map only the lower members of the 
Bridger are seen resting upon the Green River beds; but in passing south 
the country gradually rises, and each successive topographical elevation 
marks a higher stratigraphical horizon, the formation rising in broad, irregu- 
lar terraces, bounded by more or less abrupt slopes, and sometimes by bold 
escarpments of Bad Lands. North of the railway, and for a considerable 
distance to the south, is an undulating desert almost devoid of vegetation, 
its surface desolate stretches of arid, ashen-colored sand or clay, without 
any conspicuous hills. 

In the region of Church Buttes outliers of the Bridger group con- 
stitute detached bodies rising above the Plains in the most picturesque 
forms, eroded in the characteristic bad-land shapes; domed mounds and 
buttressed blocks remind one of a variety of architectural designs. The 
color here is grayish drab, with numerous stripes of greenish argillaceous 
sandstone characteristic of the lower part of the series. 

Farther to the south a second broad, irregular terrace is seen, whose 
front, under the name of Grizzly Buttes, presents an escarpment not unlike 
that already described in Washakie Basin. The forms here are usually 
soft, rounded outlines, deeply scored with sharp, parallel ravines cut down 
at short intervals. The extremely steep slopes are weathered into absolute 
smoothness. The colors are here light-gray and drab, with white and 
greenish bands; and the perspective of the front of Grizzly Buttes is cer- 
tainly one of the most remarkable geological views of the region ; not so 
architectural as the Bad Lands of Washakie Basin, but singularly im- 
pressive by the infinite variety of peculiar shapes. 

The deepest exposures of the Bridger series are laid bare in the valley 

26 K 


402 SYSTEMATIC GEOLOGY. 


of Henry’s Fork, where, as south of Turtle Bluffs, a thickness of 1,800 to 
2,000 feet is exposed. If we are right in assigning to the Wyoming con- 
elomerate a Pliocene age, it is probable that a very large amount of the 
upper strata of the Bridger series was eroded prior to the laying down of 
the Wyoming conglomerate. On the southern slope of Turtle Blufis, and 
on the north as well, have been found innumerable fossil vertebrates, together 
with a considerable number of Unio and Planorbis spectabilis. By far the 
larger amounts of the beds are gray sands and clays, but here and there 
are prominent calcareous strata. The chemical constitution of a green cal- 
careous marl upon the southern face of these bluffs will be found in the 
tables of analyses of sedimentary rocks. A second analysis was made of 
the light-green band taken from Grizzly Butte, and it was seen under the 
microscope to consist of fine grains of quartz and black mica and some 
feldspar, with a permeating cement of green clay. 

At Mount Corson and Concrete Plateau, and along the prominent 
conglomerate spur which forms the divide between Henry’s and Smith’s 
forks, the Bridger series is overlaid by great thicknesses of conglomerate, 
ranging from 200 to 600 feet in thickness, which may be an upper shore 
member of the group. 

With the exception of the Planorbis and Unio beds in the upper mem- 
bers, the greater part of the molluscan remains of the Bridger series is 
found in the lower strata. The chief forms are: 


Unio Haydenii. 

Planorbis spectabilis. 
Physa Bridgerensis. 
Goniobasis tenera. 
Viviparus paludineformis. 
Viviparus Wyomingensis. 
Pupa Leidyi. 


The chief interest of this formation arises from its remarkable fertility 
in vertebrate remains of true Eocene type. The following list, though 
by no means exhaustive, will serve to indicate the character of the Bridger 
fauna: 


EOCENE TERTIARY. 403 


BRIDGER BEDS. 
PRIMATES. 


Lemuravus distans, Marsh. 
Hyopsodus minusculus, Leidy. 
Hyopsodus paulus, Leidy. 
Limnotherium tyrannus, Marsh. 
Limnotherium elegans, Marsh. 


CARNIVORA. 
LTimnofelis ferox, Marsh. 
Limnocyon riparius, Marsh. 
Vulpavus palustris, Marsh. 
Uintacyon edax, Leidy. 
Sinopa rapax, Leidy. 
Orocyon latidens, Marsh. 
Dromocyon vorax, Marsh. 


INSECTIVORA. 


Talpavus nitidus, Marsh. 
Centetodon pulcher, Marsh. 
Entomacodon angustidens, Marsh. 
Paleacodon vagus, Marsh. 
Passalacodon littoralis, Marsh. 
Paleacodon verus, Leidy. 
CHENOPTERA. 
Nyctitherium velox, Marsh. 
Nyctitherium priscus, Marsh. 
Nyctilestes serotinus, Marsh. 
DINOCERATA. 
Uintatherium robustum, Leidy. 
Tinoceras anceps, Marsh. 
Dinoceras mirabile, Marsh. 
Dinoceras lacustris, Marsh. 
Dinoceras lucaris, Marsh. 
Dinoceras laticeps, Marsh. 


404. 


SYSTEMATIC GEOLOGY. 


UNGULATA. 
Paleosyops paludosus, Leidy. 
Hyrachyus agrarius, Leidy. 
Orohippus agilis, Marsh. 
Helaletes boops, Marsh. 
Hyrachyus Bairdianus, Marsh. 
Homacodon vagans, Marsh. 
Helohyus lentus, Marsh. 

RODENTIA. 
Paramys delicatus, Leidy. 
Mysops minimus, Leidy. 
Sciuravus nitidus, Marsh. 
Tillomys senex, Marsh. 
Tachymys lucaris, Marsh. 
Apatemys bellus, Marsh. 

TILLODONTIA. 
Anchippodus minor, Marsh. 
Tillotherium hyracoides, Marsh. 
Tillotherium fodiens, Marsh. 
Stylinodon mirus, Marsh. 
AVES. 

Bubo leptosteus, Marsh. 
Aletornis nobilis, Marsh. 
Aletornis pernix, Marsh. 
Aletornis venustus, Marsh. 
Aletornis gracilis, Marsh. 
Aletornis bellus, Marsh. 
Unitornis lucaris, Marsh. 

CHELONIA. 
Hybemys arenarius, Leidy. 
Baptemys Wyomingensis, Leidy 
Bena arenosa, Leidy. 
Anosteira ornata, Leidy. 
Trionyx guttatus, Leidy. 


EOCENE TERTIARY. 405 


SAURIA. 
Glyptosaurus princeps, Marsh. 
Thinosaurus leptodus, Marsh. 
Oreosaurus lentus, Marsh. 
Tgquanawus evilis, Marsh. 
Saniva ensidens, Leidy. 
Crocodilus Elliotti, Leidy. 
Crocodilus brevicollis, Marsh. 
Limnosaurus ziphodon, Marsh. 

OPHIDIA. 

Boavus occidentalis, Marsh. 
Boavus agilis, Marsh. 
Boavus brevis, Marsh. 
Lithophis Sargentii, Marsh. 
Limnophis crassus, Marsh. 

PISCES. 

Amia Newberrianus, Marsh. 
Amia depressus, Marsh. 
Amia Uintensis, Leidy. 
Amia media, Leidy. 
Lepidosteus glaber, Marsh. 
Lepidosteus Whitneyi, Marsh. 
Hypamia elegans, Leidy. 
Phareodus acutus, Leidy. 
Pappichthys plicatus, Cope. 
Rhineastes radulus, Cope. 


Uinta Grovp.—Of the Tertiaries immediately south of Uinta Range, 
comparatively little is distinctly known. Flanking all the alluvial valleys 
of the streams are bluffs and ridges formed of Tertiary strata, the lower 
members being chiefly rough, gritty conglomerate, passing up into finer- 
grained sandstones, and at certain points developing creamy, calcareous beds. 
The strata apparently form an unbroken line from the region of the Wah- 
satch eastward throughout the length of Uinta Valley, and across Green 
River into the valley of White River. Near the lower lands of Uinta Valley 


406 SYSTEMATIC GEOLOGY. 


the upper beds are wanting, and on the flanks of the Uinta Mountains, 
where the upper series is present it is in great measure overlaid by glacial 
débris and moraines, which generally obscure its occurrence. The verte- 
brate remains which have been found in the continuation of these beds in 
White River Valley belong to a period higher than the Bridger series. 
They even contain some forms closely approaching the lowest Miocene 
types. But exactly what relation these White River beds bear to the more 
western members of the Uinta group does not at present appear. 

There is little doubt that the main western portions around the head 
of Uinta Valley, the Du Chesne, and the region of Strawberry Valley be- 
long, as before indicated, to the Vermilion Creek group, and it is not at all 
impossible that the upper calcareous beds seen along the middle and eastern 
Uinta may represent fragmentary portions of the Green River series, which 
have thus far succeeded in resisting erosion. Some of the lowest exposed 
beds of the region are seen at Wansits Ridge, near the southeastern point, 
where they repose unconformably upon the Fox Hill sandstones, dipping at 
angles of from 8° to 10° to the southeast. In passing southward, this com- 
paratively steep dip declines to a nearly horizontal position. These beds 
consist of earthy sands and eonglomerates containing many coarsely rounded 
pebbles of the older rocks of Uinta Range. These pass up into greenish 
and reddish sandy beds, having many coarse, chocolate-colored sandstone 
members. A still higher dip is observed in these same rocks along the 
upper branches of Ute Fork, where an inclination of 25° is sometimes seen. 
But in approaching the flanks,of the mountains the sandstones are com- 
pletely overwhelmed by the rubbish of the Glacial Period, and by moraines 
eight or ten miles long. The same coarse, red sandstones appear near the 
mouth of Antero’s Creek. 

A locality of some petrographical interest was noticed between the 
upper east and west branches of Lake Fork, near the slopes of the older 
rocks along Uinta Range. Here is displayed a very thick series of yel- 
low sandstones, rather coarse in texture, developing a concretionary struct- 
ure, and yielding by erosion peculiar spire-like forms. At the foot of 
these cliffs the lower members are heavy, reddish beds, the whole exposure 
of about 600 feet dipping 4° or 5° to the south. Westward from the creek 


EOCENE TERTIARY. 407 


the Tertiary beds are seen occupying the cliffs at a height apparently of 
2,000 feet above its bed, the upper members made of coarse conglomerate, 
resembling those of Pliocene age. In the region of Strawberry Valley the 
outcrops are still further obscured by an enormous amount of overlying 
disintegrated soil and a thick growth of forest. Some outcrops of sandstone 
along the eastern slope of the Wahsatch, of very high dips, were referred 
to the Cretaceous, but from stratigraphical reasons only. As north of the 
Uinta, the Tertiary series seem to thicken greatly on approaching the Wah- 
satch, which is unquestionably to be accounted for by the fact that that 
range marks the shore of the land-mass against which the earlier Eocene 
lake was traced; and the lake being very deep near its own shore, the 
detrital material accumulated more thickly there than to the east. When 
the Tertiaries south of Uinta Range are carefully unravelled, as they doubt- 
less will be by Powell and Gilbert, it will probably be found that the most 
recent Eocene group, as developed in White River Valley, is unconform- 
able with all the earlier Eocene groups. It is a shallow deposit, of which 
not over four hundred feet are seen, and in all probability is the sediment 
of a very restricted post-Bridger lake, wholly south of Uinta Range, and 
the last member of that remarkable series of Eocene lakes whose great 
deposits are piled unconformably over one another in the region. To this 
group alone should the term Uinta be applied. As provisionally used on 
the Fortieth Parallel Atlas, Uinta group was a term stretched for conven- 
ience to cover all the Tertiaries south of Uinta Range, of whose true sub- 
divisions we were ignorant. 
The following list comprises some of the more important vertebrates 
of the true Uinta series : 
UINTA GROUP. 

Hyopsodus gracilis, Marsh. 

Diplacodon elatus, Marsh. 

Epihippus Uintensis, Marsh. 

Epihippus gracilis, Marsh. 

Agriocherus pumilus, Marsh. 

Amynodon advenum, Marsh. 


SEC TLO Nee 
MIOCENE TERTIARY. 


Wuite River Grovup.—Over a vast portion of its area the geological 
province of the Great Plains has a covering of Pliocene Tertiary beds, 
varying in thickness from 2,000 feet down to a few hundreds. The 
streams, which flow from the front of the Rocky Mountains and join the 
various affluents of the Missouri, have not infrequently cut through this 
covering of Pliocene and exposed the underlying rocks. In several places 
it is found that the Pliocene rests unconformably upon beds of upper 
Cretaceous, which lie either horizontal or in slight undulations. At other 
points, notably the valleys of Platte River and White River, the wide- 
spread Pliocene has been found to be directly underlaid by beds of Mio- 
cene age, characterized by an ample and typical fauna. Along the 41st 
parallel, at the extreme eastern end of the belt of Fortieth Parallel work, 
the Pliocene strata have been eroded away, leaving a rudely terraced 
escarpment, which faces the south, overlooking a nearly level plain com- 
posed of the beds of the Fox Hill and Laramie Cretaceous. East of the 
Denver Pacific Railroad and south of the 41st parallel a small development 
of Miocene beds is seen to be interposed between the Cretaceous and the 
Pliocene; being in fact an eroded edge of the sheet of Miocene which, over 
a considerable area of the Plains, underlies the Pliocene. 

The precise area and boundaries of this Miocene lake cannot yet be 
definitely assigned. It is clear that the beds brought to light upon North 
Platte and White rivers, and at the locality just mentioned at Chalk Bluffs, 
near the Denver Pacific Railroad, belong to the same lake. Messrs. KE. 8. 
Dana and G. B. Grinnell, in their valuable geological reconnoissance from 
Carroll, Montana, to the Yellowstone National Park,* have brought to light 
in the vicinity of Camp Baker, Montana, a further development of Miocene 
beds, here as elsewhere on the Plains capped by Pliocene, both series 
containing characteristic fossils. The altitude at which these beds were 
observed by them, 5,000 feet, induced them to suppose that the rocks they 


- * Reconnoissance of Capt. William Ludlow, 1875. 
408 


MIOCENE TERTIARY. 409 


examined belonged to an independent lake, shut off from the great Miocene 
lake of the Plains, the elevation being 2,000 feet greater than that of the 
beds exposed on White River. But since the small exposure falling within 
the limits of the Fortieth Parallel Exploration has an altitude of nearly 
6,000 feet, and since there is no known barrier which could have separated it 
from the Miocene rocks upon Platte River, as well as those displayed upon 
White River, I have felt bound to assume that the Chalk Bluff beds, as 
well as those displayed farther east, near the northern boundary of Kansas, 
are a part of a general Miocene lake, the beds of the region having under- 
gone broad changes of level since the Pliocene period. These Miocene 
beds evidently pass southward as far as the northern boundary of Kansas, 
and continue northward into Montana. 

At the somewhat ambiguous locality of Fort Union, on the Upper 
Missouri, occur beds bearing molluscan and vertebrate faunz, which corre- 
late directly with the higher horizons of the Laramie Cretaceous. From 
later beds at the same place has been collected a rich flora corresponding 
with great exactness to the Miocene beds of Manitoba, of Greenland, and 
of northern Europe. It has never been announced whether these two series 
of beds were conformable. Both horizons have been embraced in the Fort 
Union group, whereas there is every probability that the rocks at that locality 
bearing Dinosaurians are Laramie, while the upper distinctly Miocene series 
is with equal probability to be correlated with the known Miocene of the 
Plains. At Chalk Bluffs the Laramie Cretaceous and White River Miocene 
are observed in immediate contact, with but slight angular unconformity. 
Cretaceous and Miocene fossils occur in close proximity, and in the absence 
of a clear understanding of the stratigraphy this locality might easily appear 
as paradoxical as Fort Union. 

In the Fortieth Parallel Exploration we have, therefore, only a very 
limited exposure near the edge of the Miocene lake, where it washed the 
foot-hills of Colorado Range. That the beds extended south over the Cre- 
taceous area of the Plains, forming the southeast corner of Map L, is un- 
questionable from the Miocene escarpment. The strata of which the Chalk 
Bluff escarpment is composed rest unconformably upon the gently dipping 


sandstones and shales of the Laramie or uppermost group of the Cretaceous. 


410 SYSTEMATIC GEOLOGY. 


The latter group are here nearly horizontal, but if examined over consid- 
erable areas are found to be thrown into very slight undulations, and toward 
the western limit of the outcrop to have a perceptible dip to the east. 

Prior to the deposition of the Miocene beds, the Cretaceous had under- 
gone a great deal of deep erosion, which left the surface in soft undula- 
tions of very gentle grade, the details of the surface rarely showing any 
abrupt topographical forms. The entire escarpment, including the Miocene 
and Pliocene beds, reaches a height of 700 feet above the Cretaceous plains. 
The small streams of the Plains have worn numerous narrow ravines down 
the escarpment, cutting back to a considerable distance, and offering ad- 
mirable sections in which to observe the character of the beds. 

Following the escarpment westward, it becomes evident that the Mio- 
cene deposits abut against the very lowest base of the foot-hills, always 
limited by the upper Cretaceous rocks, whereas the overlying Pliocene 
overlaps to the westward, and formerly rose high against the range, as is 
shown from Box Elder Creek northward to the Chugwater. In other 
words, the Miocene lake was of much lower level, covered, as far as we now 
know, a smaller area, and was limited in this region along the east by the 
gently upturned upper Cretaceous beds. 

In the limited exposure from Carr Station eastward along the tributaries 
of Owl and Crow creeks, the Miocene shows a thickness of about 300 feet, 
the altitude of the uppermost strata being here about 5,800 feet, or fully 
2,200 feet higher than the contact between the same beds upon White River. 
At this locality the separation between the two series is not at all one of 
angle or of any abrupt change of material. The conglomerate mentioned 
by Dana and Grinnell to the north as the dividing-line between the strati- 
graphically conformable Miocene and the Pliocene, is here wanting, and the 
division is established solely on palzeontological ground. The beds consist 
of constantly varying thin layers of gray and creamy clays, fine sands, and 
marls. The latter, in broad white beds, presents so chalky an appearance 
as to have suggested the name of the region, Chalk Bluffs. There are nu- 
merous ferruginous layers where the sandy material is cemented by brown 
earthy iron oxyds, whose more compact outcrop may be traced along the 


varied forms of the escarpment for several miles 


MIOCENE TERTIARY. 411 


The lower 300 feet are characteristic Miocene, and have yielded nu- 
merous typical Miocene vertebrate fossils. The following list is made up 
largely from this locality, but partly from other points of the same horizon, 
also on the Great Plains : 


MIOCENE OF THE PLAINS. 


Laopithecus robustus, Marsh. 
Drepanodon intrepidus, Leidy. 
Drepanodon primevus, Leidy. 
Dinictis felina, Leidy. 
Amphicyon vetus, Leidy. 
Amphicyon angustidens, Marsh 
Hyanodon horridus, Leidy. 
Hyanodon cruentus, Leidy. 
Hyanodon crucians, Leidy. 
Oreodon Culbertsoni, Leidy. 
Oreodon gracilis, Leidy. 
Eporeodon major, (Leidy) Marsh. 
Eporeodon bullatus, (Leidy) Marsh. 
Merycocherus proprius, Leidy. 
Agriocherus antiquus, Leidy. 
Percherus probus, Leidy. 
Leptocherus spectabilis, Leidy. : 
Protomeryx Hallii, Leidy. 
Leptomeryx Evansii, Leidy. 
Leptauchenia major, Leidy. 
Poebrotherium Wilsoni, Leidy. 
Hyopotamus Americanus, Leidy. 
Lilotherium Mortoni, Leidy. 
Elotherium superbum, Leidy. 
Elotherium bathrodon, Marsh. 
Elotherium crassum, Marsh. 
Menodus giganteus, Pomel. 
Brontotherium ingens, Marsh. 


412 SYSTEMATIC GEOLOGY. 


Brontotherium gigas, Marsh. 
Diconodon montanus, Marsh. 
Rhinoceros Nebrascensis, Leidy. 
Rhinoceros occidentalis, Leidy. 
Mesohippus Bairdi, (Leidy) Marsh. 
Mesohippus celer, Marsh. 
Mastodon mirificus, Leidy. 
Paleolagus Haydeni, Leidy. 
Ischyromys typus, Leidy. 
Paleocastor Nebrascensis, Leidy. 
Eumys elegans, Leidy. 

Leptictis Haydeni, Leidy. 

Ictops Dakotensis, Leidy. 
Meleagris antiquus, Marsh. 


Truckee Grovup.—Passing westwardly from Colorado Range, the en- 
tire country, as far west as the western base of Wahsatch Range, is alto- 
gether free from deposits of the Miocene. The broad area of Tertiary 
which oceupies North Park and the upper valley of the North Platte is mainly 
posterior to the period of basaltic eruptions; and from its analogy with 
deposits in connection with the great basaltic outflows of Idaho, Oregon, 
and Nevada, it is assumed that these Tertiaries are Pliocene. The Plio- 
cenes of the Great Plains also bear the same relation to the basalt north of 
the limits of our work, and there are further strong lithological grounds for 
referring the limited lacustrine Tertiaries of North Park and the Platte to 
the Pliocene. 

The basin of Salt Lake, unlike the country between it and the Great 
Plains, is at present low enough to have been the receptacle of Miocene 
beds; but there is every reason to suppose, as will be seen hereafter, that 
the depression of the Utah Basin took place at a date posterior to the close 
of the Miocene age, and that during the Miocene period it was, like the 
country to the east, a land area without considerable lakes The same is 
true of middle and eastern Nevada, and it is not till we arrive at the meridian 
of 117° that we again reach strata which may be referred with any degree 


MIOCENE TERTIARY. 413 


of probability to the Miocene age. This longitude marks approximatively 
the division between the higher plateau country of Nevada and the western 
Nevada Basin. The valleys of the latter area sink to an altitude of 3,700 
feet, while those of the plateau country to the east are 5,000 and 6,000 feet. 

A line of great geological change has been indicated as existing imme- 
diately west of the Battle Mountain group and Toyabe Range. The main 
feature of this change has been already indicated as the complete cessa- 
tion of Palzeozoic strata, which have continued from far to the east up to 
this meridian, and the sudden coming in of ranges made of Triassic and 
Jurassic rocks which continue westward into California. Besides the occur- 
rence of these rocks of the middle age, there appears with equal sudden- 
ness, cropping through the immense Quaternary deposits of the valley, and 
in some instances in the eroded ravines of the rhyolite ranges, a series of 
upturned sedimentary beds displaying a very great total thickness, prob- 
ably not less than 4,000 feet, the series being older than the rhyolites, partly 
older and partly contemporaneous with the trachytes. A large portion of 
the material of the group is made of trachytie muds, which carry, especially 
in Oregon, enormous numbers of Miocene fossil mammals. 

The rocks of the group are limited on the east, within the boundaries 
of our Exploration, by the 117th meridian, and on the west by the abrupt 
wall of the Sierra Nevada. Northward they extend through Oregon and 
pass into Washington Territory, having their greatest development on 
Crooked River, the John Day, and the Malheur. South of our work they 
are well known in the valley of Walker River, but beyond that southward 
I am not aware of their having been observed. 

An immense upturned series of fresh-water Tertiaries is displayed on 
a grand scale in the region of Cajon Pass, in southern California. Thus 
far I am not aware of these having yielded more than uncharacteristic fresh- 
water mollusks and a few unidentifiable fragments of mammalian bones. 
In future this is likely to be correlated with the lacustrine Miocene of the 
north. 

The rocks of this series, within the limits of Map V., are always found 
upturned from 10° to 25°, and wherever observed in connection with ba- 
saltic eruptions they are cut through and overflowed by the basalt. The 


414 SYSTEMATIC GEOLOGY. 


rhyolites also break through and overflow them, while the sub-lacustrine 
eruptions of the trachytic period are intercalated in the Miocene series. 

On the eastern half of Map V. the Miocene first appears upon Silver 
Creek, at the western base of Toyabe Range, in latitude 39° 95’. Here 
and at Boone Creek, surrounded and overflowed by enormous masses of 
rhyolites, are some beds inclining from 15° to 20°, composed of light buff 
and ashy strata, very thinly bedded in some places, and in others made up 
of broad belts of uniform sediment 30 or 40 feet thick. They are charac- 
terized here and there by passages of chalcedonic material, which are 
local silicifications in situ, and in the softer passages by the presence of 
rolled specimens of fossil vertebrate bones, which are always too imperfect 
for identification. Under the microscope it is evident that this material is of 
voleanic origin, consisting of particles of crystalline grains of sanidin, with 
more or less magnetic iron, hornblende, mica, and a little quartz. There is 
no direct proof of their Miocene age, but they are referred to the Truckee 
group from their evident recent nature, and the fact that they immediately 
antedate the massive rhyolites. 

Similar rocks, even more conspicuously made up of volcanic materials, 
are seen in the valley of Reese River to the north and west of Silver Creek, 
and also around the flanks of Lone Hill Valley, between the Shoshone and 
Augusta Mountains. Here the middle of the broad depression is occupied 
by heavy accumulations of Quaternary, which conceal all but a belt of 
Tertiary rocks, that line the edge of the valley and are immediately overlaid 
by the massive eruptions of rhyolite which form the greater part of the two 
bounding ranges. A similar inclined mass of voleanic and sandy sediments 
lies to the west of the Augusta Mountains, in like relations to the Quater- 
nary valley and overlying rhyolites. 

This group again appears near the southern end of Havyallah Range, 
where a broad mass of basaltic rock has outpoured along the eastern face of 
the range, burying the greater part of the Miocene beds. Similar unchar- 
acteristic exposures are seen directly south of Buffalo Peak and east of 
Lovelock’s Station on the foot-hills of West Humboldt Range. The sedi- 
ments are here less characteristically volcanic, and seem to be made up 
partly of volcanic material, but largely of coarse sands and gravels, and 


MIOCENE TERTIARY. 415 


from their immediate contact with the Triassic rocks it is fair to assume 
that these exposures represent the lower limits of the series, while the soft 
volcanic beds displayed in the Shoshone and Augusta Mountains are with- 
out suggestion as to their position in the series. . 
I have merely mentioned these outcrops, because they are of some 
local importance, and in general their lithological resemblance and their 
relative position to the other rocks refer them to the one group. Future 
work may add the necessary proof of age to these scattered exposures. 
The most important and characteristic development of this series within 
our limits is at the Kawsoh Mountains and along the southern extremity of 
Montezuma Range. The northern and eastern portion of the Kawsoh 
Mountains and the valley which lies north of them, separating their broken 
detached group of hills from the end of Montezuma Range, together offer a 
section of about 2,300 feet of Miocene beds, noting from the top as follows: 
1. The upper 1,200 feet consist entirely of drab, mauve, gray, pale-buff, 
and white stratified trachytic tuff, intermixed with more or less 
detrital material. The beds are characterized by rapid changes of 
color and texture, are of very variable coarseness, and have a pre- 
vailing amount of glassy fragments, as if an enormous amount of the 
material were the glassy scoria and rapilli of violent and long-con- 
tinued trachytie eruption. At intervals are beds of pure gray sand 
with a few seams of slightly marly clay. The microscope shows 
that this entire series is made up of angular and sub-angular frag- 
ments, many of them excessively small. There are some singular 
chalcedonic strata, one to two feet thick, of which the lower 
stratum-plane is exceedingly rough, resting upon the trachytic 
tuff and including a great many minute fragments of the volcanic 
material, the upper surfaces being rudely botryoidal, the protuber- 
ances reaching the size of an egg. Toward the lower edge of this 
great series of trachytic tuffs, the upper limits of which are nowhere 
seen, the proportion of true detrital material—quartz and feldspar 
sand—becomes rapidly greater until the tuff is underlaid by — 

2. Coarse, sandy grits, gray and yellow fragments, partially rounded, jc, 

partially angular, with a slight proportion of calcitic material. 250 


416 SYSTEMATIC GEOLOGY. 


Feet. 

3. Saccharoidal limestone, rich in fresh-water mollusks. .-..-.------ 60 

4. Marly grits, yellow and drab, rather coarse. .-..-----...-+.---- 40 
5. Fine-grained, friable, buff and gray sandstone, having a peculiarly 

sharp, ovitty feel 2c< 22122 eee Ce ee 70 

6. Variable cray sandstones!) 2222+. 2 eee eee 100 

7. A marly erity. 22 12.36 cee eee ete 50 or 60 

8.. White and *yellow infusomal silica 22222 9= ee 200 to 250 


9. Palagonite tuff, base never seen, 250 feet being maximum exposure, 


No lower members than the bed of palagonite tuff are observed in 
the Kawsoh Mountains, or in the southern end of the Montezuma; but 
in Warm Spring Valley, a small depression in the basaltic hills a few miles 
north of Hawes’s Station, on Carson River, the palagonites, there remarka- 
bly well developed, are seen to be underlaid by a light siliceous clayey 
bed made up of fine silt and comminuted infusoria. It is always far less 
pure than the white infusorial beds above the palagonites. Here, as every- 
where, the series has an inclined position, dipping 15° to 20°. 

Miocene palagonite has only been observed by us in this litthke Warm 
Spring Valley, at the northeast corner of the Kawsoh, and at the southern 
point of Montezuma Range. We have nowhere over 250 feet exposed. 

In the Kawsoh exposure it is rather uniform, made up of yellowish- 
brown, decomposed-looking material, varyingly mixed with sand, and north- 
west of Mirage Station, in a little ravine at the foot of the rhyolitic hills, it 
is a rather coarse breccia, containing decomposed fragments of a somewhat 
vesicular augitic rock, the binding material in this case being pretty pure 
palagonite. Microscopic sections of the enclosed fragments of rock show 
a richly augitic material, in which a considerable glassy base has suffered 
extreme devitrification. Not only plagioclase but orthoclase is present. In 
passing from the outside inward, the section of these fragments shows a 
progressive palagonitic decomposition of the augite. 

In the region of Hawes’s Station, on Carson River, it is finer-grained, 
more uniformly yellowish-brown, and consists of a purer palagonitic material. 
In this case it is free from carbonate of lime. The palagonite of Fossil 
Hill, at the northern end of Kawsoh Range, when treated with acids, shows 


MIOCENE TERTIARY. 


417 


avery feeble effervescence. Our purest type of palagonite, that of Hawes’s 


Station, has been subjected to analysis, with the following result : 


Taras) 2 5 Ai Ait ee eee re 


IROLASSA Ree ee nee eS 


WVicite Lee tee on ee ere eee ee oe 


100.00 


50.88 
14.37 
13.30 
6.18 
4.14 
1.86 
0.93 
8.34 


100.00 


For the optical character of this palagonite and its microscopical beha- 


vior the reader is referred to Vol. VI. of this series. 


For purposes of com- 


parison with other distant occurrences of palagonite, I give here three 


analyses. No. 1 is a palagonite from Iceland, collected between Thing- 
vellir Lake and the Geyser (Bunsen*). No. 2 is from James Island, Gala- 


pagos (Bunsen). No. 3 is from Dyampang-Kulon, Java (Prélsst). 


No. 1. 

Sill Caleyene Mepaernestan ens Eat oles ee 41, 28 
PAV ToUn TYE ea 11. 03 
iermiczoxyd) 22) 22cm. Se NSS 2, 
aiineme meets ee 8.75 
IMCS oe er Sitch aire 3 6.49 
SKOCGE) S Goees 0. 62 
ROtassaMee rte te sees ee 0. 65 
Wintenrere te mre sts fois ok. st 17. 36 
100. 00 


No. 2. 
36. 93 
11.56 
10. 71 

7. 95 

6.28 

0.55 

0.78 
25. 24 


100. 00 


No. 3. 
37.57 
15.18 
13. 07 
6. 02 
5. 58 
0. 79 
ya W| 
19.61 


100. 00 


The Javan occurrence, described by Junghuhn, like our own, forms 


stratified deposits in a series of upturned Tertiary rocks. 


* Poggendorff Annalen, 1857, p. 219. 


\ « a 
Comparing our 


t Neues Jahrbuch far Mineralogie, 1869, p. 434. 


27 K 


418 SYSTEMATIC GEOLOGY. 


palagonites with all these others, a remarkable difference may be observed 
between the silica equivalents, the Nevada specimens carrying about 10 
pen cent. more than the others. The Icelandic and Galapagos palagonites, 
as well as those described by Sartorius von Waltershausen from Etna, are 
clearly derivable from doleritic eruptions, whereas our Miocene palagonites 
most certainly antedate all the basaltic period. 

In the stratified series overlying the palagonite, as before indicated, is 
a great thickness of purely trachytic tuffs, and from fissures through this 
stratified series after its complete deposition have outpoured the entire rhy- 
olite series, and again, still later, the basalts, which are generally unaltered 
and directly overlie the upturned edges of the palagonite beds, the latter 
having suffered no inconsiderable erosion prior to the basaltic period. The 
reference of the palagonite and the accompanying stratified rocks to the 
Miocene will be accounted for later. For the present it is sufficient to 
assert that we have no knowledge of any basaltic eruptions until long after 
the consolidation and subsequent upheaval of the Miocene palagonites. 
Throughout Nevada, it is true, the basalts precede the visible Pliocene beds, 
which in many cases rest horizontally against the somewhat eroded flanks 
of the basaltic hills. <A little north of our work, however, in the basin 
of Snake River, it is seen that there were basaltic eruptions in the middle 
of the Pliocene period, which overflowed the earlier lacustrine beds of the 
period, and in turn are themselves overlaid, as in Nevada, by the main 
later Pliocene series. 

As a matter of geological date, it is perhaps unsafe to say that the 
basalts are entirely within the Pliocene. The evidence of the Pliocene 
river system of the Sierra Nevada would go to show that the basalts of 
that country were in part at least post-Pliocene. This evidence coin- 
cides with the relations in Idaho. Thus far, however, in western Ne- 
vada, it would seem that there were no Pliocene deposits earlier than the 
basalts, whence we infer that Nevada possessed during the pre-basaltie part 
of the Pliocene age a free drainage to the sea. As between the trachytes, 
rhyolites, and basalts, the order established by Von Richthofen has been 
found to hold with remarkable persistency over the Fortieth Parallel. It 
was, then, with no small surprise that we discovered palagonitic tuffs in 


MIOCENE TERTIARY. 419 


early Miocene strata overlaid by enormous thicknesses of trachytic mud, 
and subsequently disturbed and overflowed by rhyolites and basalts. 

This brief sketch of the relations of the beds to the subsequently 
erupted rocks shows at once that the palagonites are not derivable from the 
products of the basaltic period. In looking back to the pre-trachytic augitic 
rocks for a source for these palagonites, we have only the diabases of the 
middle age, whose period of ejection is assigned to the close of the Jurassic, 
and the rare augitic propylites and augitic andesites, which are clearly 
within the Tertiary period. A comparison of the analyses of our augitic 
andesites with the true basalts demonstrates a constant difference in silica, 
amounting on an average to 8 or 10 per cent. Since the andesites, both 
hornblendic and augitic, clearly came to the surface before the period of 
the trachytes, and since this basin of the Miocene lake was the scene of 
considerable activity at the period of the augite-andesites, it seems not an 
unwarrantable assumption that the palagonites were derived from the augite- 
andesites. With this the date of their appearance as preceding the trachyte, 
their high silica-tenure as compared with the palagonites derived from do- 
lerites, and the presence of orthoclase in the included fragments of the palag- 
onitic breccias, would thoroughly coincide. In the impure parts of the 
palagonite tuff the microscope shows occasional but rare shields of infusoria. 
This is especially true at the upper limits of the palagonite beds, where 
they pass rapidly into the pure-white infusorial silica. 

Among the basaltic tuffs and decomposed basaltic materials in the 
vicinity of Black Rock, near the northern edge of the western half of Map 
V., among many curious basaltic products was observed a certain bed of 
soft, brown breccia, of which the cementing material is palagonitic. There 
is no doubt in this case that, like the deposits of Iceland and Etna, it is 
simply a local dependent of the basaltic eruptions. 

The infusorial silica overlying the palagonite has its most important 
outcrops at Fossil Hill and along the whole northeastern edge of the 
Kawsoh Hills, and skirting their northern base nearly as far west as Warm 
Spring Valley; also near the site of Sam’s Station, northwest of Mirage 
Station, and on the banks of Little Truckee River, between Pyramid 
and Winnemucca lakes; also west of Reno Station, on the Central Pacific 


420 SYSTEMATIC GROLOGY. 


Railroad, near the boundary of California. The deposits of Warm Spring 
Valley and of Carson Valley are obscure, and show no very great thick- 
ness of beds. That near Hunter's Station, west of Reno, is an extensive 
exposure on the right of the railway-cut in approaching California, and 
consists of several hundred feet (certainly as many as 300) of pure-white, 
pale-buff, and canary-yellow beds of remarkably pure infusorial earth. 

At Fossil Hill, on the northeast point of the Kawsoh Mountains, it 
appears overlying the palagonite tuff, and is succeeded above by marly 
erits. All along the northeast slopes of the mountains the cliffs and hills 
of infusorial silica appear in an uptilted position, their summits deeply 
eroded and overwhelmed by caps of basaltic rock. The bedding is here 
for the most part very thin, but certain of the strata reach eight or ten 
feet in thickness, of comparatively uniform material, without bedding- 
planes. Occasional fragments of willow leaves are observed. The lower 
members are pure-white, the upper show some interstratification of earthy 
impurities, and in the neighborhood of the overlying grits they are often 
pale-yellow. The white beds are remarkably light, cut easily with the 
knife, and have the earthy feel of chalk. They are almost entirely free 
from carbonate of lime, except in the uppermost yellow members imme- 
diately underlying the grits and sands, where there is a varying but always 
small proportion of carbonates. An analysis of the pure-white product is 
given in the table of analyses of stratified rocks. 

Specimens of these white strata were subjected to microscopic analysis 
by Dr. C. E. Ehrenberg, of Berlin, who found forty-six distinct species 
of diatomes. Twenty-eight of these forms have been classed as Polygas- 
tera, and eighteen as Phytolitharia, the most abundant species being — 


Gallionella granulata. 
Gallionella sculpta. 
Spongolithis acicularis. 


In a lavender-colored bed far up in the series above the acidic tuffs, 
further sandy beds are observed in the same section, containing more or 
less infusoria, in which the following species were recognized by Mr. 


Charies E. Wright : 


MIOCENE TERTIARY. 421 


Gallionella ? 
Spongolithis acicularis. 
Pinnubaria inequalis. 
Cascidoniscus radiatus. 


Near White Plains Station the palagonitic tuffs, with the overlying 
infusorial earths, are directly broken through by a dike of pearlitic rhyo- 
lite, and afterward, after considerable erosion, overpoured by basaltic flows. 

On Little Truckee River, a few miles above its mouth, the right bank, 
which is here quite a considerable cliff, displays a front of soft, white, 
infusorial rocks, dipping about 30° away from the river, or to the south- 
east. The white cliffs overhang the river, and large blocks, which are 
easily detached from the irregular, rough, chalk-like surface, roll down the 
abrupt slope into the river, and by their extreme lightness float on the 
surface, shooting quickly out of sight on the rapid current. It was not the 
least curious of our geological experiences to dislodge hundreds of these 
large blocks from the face of the cliff and see them drift away on the river 
surface in a tossing flotilla. Stems and leaves of plants of the willow family 
are not unfrequently found in the infusorial beds; but so far as we have 
observed they contain no molluscan remains or vertebrates. The upper 
members are rather more impure, are very finely stratified, and in some 
instances approach a quartzitic texture. They have apparently been meta- 
morphosed, possibly by the contact of some lava-flow, resulting in an inter- 
esting series of colors—buff, lavender, gray, and bright brick-red. In these 
upper beds the surface of the slope is covered with thinly laminated chips. 
Under the microscope, though often showing traces of infusorial structure, 
the indurated strata are for the most part of a cryptocrystalline texture. 

The sections of these rocks exposed are so exceedingly limited, in all 
cases nearly covered by Quaternary deposits, or the horizontal Pliocenes, 
or flows of rhyolite and basalt, that, with the exception of the Fossil 
Hill locality, we are unable to determine the limits of these infusorial beds. 
There, in passing up, the main mass of 250 feet is overlaid by marly grits, 
which occupy about 150 feet. These are all more or less infusorial, as the 
inicroscope shows, and carry, besides the remains of diatomes, not a little 
carbonate of lime. 


422 SYSTEMATIC GEOLOGY. 


They are succeeded above by the saccharoidal limestone, which is 
best shown on Fossil Hill, but also appears again west of White Plains 
Station, and in the hills in the neighborhood of Valley Wells. This lime- 
stone is usually cream-colored, and is cryptocrystalline in texture. At 
Fossil Hill it carries a great number of fresh-water mollusks, of which the 
following are the most important species: 


Carnifex Binneyi. 
Carnifex Troyoni. 
Ancylus undulatus. 
Melania sculptilis. 
Melania subsculptilis. 
Spherum rugosum. 
Spherum Idahoense. 


And the similar occurrence at Valley Wells gave a partial repetition of this 
list of species. 

Where the parallel of 43° 30’ crosses Montezuma Range, there is a 
peculiar northeast-and-southwest break, which severs the range into two 
parts. This depression is occupied, as Map V. well illustrates, by a series 
700 or 800 feet thick of the upper portion of the Truckee Miocene, inclined 
at very gentle angles, usually not over 2°, resting on the south unconform- 
ably upon the granite, to the east and west concealed by Quaternary 
deposits, and over a long stretch of country northwest of Indian Pass 
overlaid by sheets of more modern basalt. All the strata are excessively 
soft, and have suffered much from erosion, the resulting forms being soft, 
gentle slopes, for the most part débris-covered, but here and there showing 
the edges and surfaces of the Miocene beds. They are altogether volcanic 
materials of the period of trachytic eruptions. A few layers are compacted, 
but for the most part they are friable pale-gray, ashy, and lavender pumices 
and hyaline sands, varied with beds of orange, red, yellow, and purple, 
with some nearly pure white. There is the utmost variety in the texture 
of these beds, some being excessively fine, others rather coarse, containing 
a good deal of quartz sand. They no doubt represent the upper portion of 


the series already described above the grits and limestone of the Fossil 


MIOCENE TERTIARY. 423 


Ilill section. So far they have not been seen to contain any organic 
remains, and are referred to the Miocene by their position under the basalt, 
and from lithological resemblance to the pumice and tuff beds which out- 
crop so characteristically between Kawsoh and Montezuma ranges. Unim- 
portant outcrops are seen on the eastern slope of the Sahwave Mountains, 
and on the western slope of Truckee Range, north of Luxor Peak. 

There is but one other locality of any importance falling within the 
limits of our observation, and that is the débris-covered slopes south of the 
Daney Mine, in the Washoe mining district. There the excavations for 
mining-shafts in the soft upper rocks have brought to light a series of 
volcanic tuffs belonging to the age of the propylites, being, in fact, 
made up of rapilli and sand of propylitic eruptions. They contain 
numerous leaves of Tertiary plants, chiefly willows, and are overlaid by 
gritty sands and some fine, white, clayey beds, the latter appearing in very 
small amount. It is conjectured that these are the earliest of the Miocene 
deposits, and if we could obtain a full section anywhere they would prob- 
ably be found underlying the palagonite tuff, which we conceive to rep- 
resent the age of the augite-andesites. The hornblende-andesite sands 
themselves would doubtless be represented in the sequence of sediments. 

No vertebrate remains have been found upon the area of Map V., 
except a single rhinoceros tooth from the grits of the Kawsoh Mountains, a 
species which has been pronounced to be probably Miocene. The fresh- 
water mollusca of the saccharoidal limestone of Fossil Hill would not 
alone afford sufficient data for referring this series to the Miocene, although 
Professor Meek, independently of any other reason, made this assignment. 
The main reason for classing the whole group as Miocene is, that farther 
north in Oregon, upon John Day, Des Chutes, and Crooked rivers, Pro- 
fessor Marsh’s researches have brought to light an immense formation, 
computed by him to be 3,000 or 4,000 feet thick, containing numerous 
vertebrate remains of clearly Miocene type. These Oregon beds are all 
in inclined positions, earlier than basaltic eruptions, and the main material 
of his whole series, as I have determined by microscopic studies, is of strati- 
fied trachytic pumices, tufts, and hyaline sands. The Oregon Miocene is 


apparently the direct northward continuation of the Nevada formation. Be- 


424 SYSTEMATIC GEOLOGY. 


sides the parallelism between the two series, is the fact of an overlying un- 
conformable Pliocene in each case. The mollusks from Fossil Hill, and the 
rhinoceros tooth, distinctly refer the Nevada strata to the Miocene. The 
overlying Pliocenes and basalts are similar and of identical position in each 
case; and this, together with the identity of material and similarity of dis- 
turbed position, has led us finally to refer our Truckee group to the Mio- 
cene. 

The following list of fossils, characteristic of the series, will serve to 
convey a general idea of the fauna of the Miocene lake of Oregon: 


OREGON MIOCENE. 


Eporeodon occidentalis, Marsh. 
Eporeodon superbus, (Leidy) Marsh. 
Thinohyus lentus, Marsh. 

Thinohyus socialis, Marsh. 
Rhinoceros Pacificus, Leidy. 
Diceratherium annectens, Marsh. 
Diceratherium crassum, (Leidy) Marsh. 
Diceratherium armatum, Marsh. 
Diceratherium nanum, Marsh. 
Miohippus annectens, Marsh. 
Miohippus Condoni, (Leidy) Marsh. 
Miohippus anceps, Marsh. 

Allomys nitens, Marsh. 

Moropus distans, Marsh. 

Moropus senex, Marsh. 


SHCLTLON LE. 
PLIOCENE TERTIARY. 


Nroprara Grour.—The Pliocene occurrences of the Fortieth Parallel 
are altogether lacustrine. Contemporaneous marine deposits are found west 
of the Sierra Nevada, and form important members of the upturned sedi- 
mentary series of the Coast Ranges of the Pacific. But east of the Sierra 
Nevada, all the way to the valley of the Mississippi, there are no very broad 
intervals, except the basin of Green River, which are not characterized by 
deposits of Pliocene lakes. 

East of Colorado Range, in the geological province of the Great 
Plains, there is no single formation of more geographical importance than 
the deposits of the great Pliocene lake, a sheet of water which stretched 
from the base of the Rocky Mountain system eastward well toward the 
Mississippi Valley, and extended in a north-and-south line from the low- 
lands of Texas to an unknown distance into British America. It is the 
latest considerable geological formation of all this vast area of Plains, and 
is continuous over a great portion of its surface. Where the Rocky 
Mountains, against which it abuts, are particularly high and form powerful 
condensers of moisture, the resultant streams have carried away from the 
neighborhood of the front of the range considerable areas of Pliocene, with 
their underlying Miocene beds, leaving the still underlying Cretaceous 
formation as the surface-member of the plains. It is very interesting in 
the area of Map V. to notice the presence of the Tertiary strata against the 
eastern base of the hills, where the mountain-mass is low and relatively 
deficient in strong streams, and its absence abreast of the loftier parts of 
the range, where powerful streams are frequent enough to have completely 
eroded away the soft Tertiaries. 

The most conspicuous topographical fact in Colorado Range, as shown 
upon the limits of Map L., is the great and sudden rise of the range south 
of the 41st parallel. From the northern edge of the map down to the 


heads of Cache la Poudre River, the average mountain-mass is low, its 


425 


426 SYSTEMATIC GEOLOGY. 


forms are comparatively soft and rounded, it never attracts any very great 
amount of moisture, the streams which flow from it are small, and in con- 
sequence the sheet of Pliocene beds lies uneroded upon its eastern base. 
The Cache la Poudre itself forms the first of the powerful streams which 
derive their abundant waters from the melting snows of the lofty ridge. It 
is interesting to observe that abreast of this sudden elevation the Tertiaries 
along the eastern base of the mountain have been entirely eroded away, 
leaving broad, low plains of Cretaceous, the escarpment of the southern 
edge of the Tertiary exposures clearly showing that their absence to the 
south is due to erosion. 

As exposed upon Chalk Bluffs, the plane of demarkation between the 
Pliocene and Miocene, as before stated, is drawn on paleontological evidence 
alone, the upper 300 or 400 feet being of Pliocene beds, which from that lati- 
tude northward completely cover the whole of that portion of the Plains 
which falls within the limits of Map I. Over this extent of country, the posi- 
tion of the Pliocene strata is exceedingly important, as illustrating certain 
changes which have taken place since their deposition. The altitude of 
the contact-plane between the Pliocene and the Miocene is in the region of 
6,000 feet upon the surface of Chalk Bluffs. The Pliocene strata rise in 
altitude along the base of the mountains in the region of Shelter Bluffs, on 
parallel 41° 30’, to over 7,000 feet. Northward, on the northeast corner 
of the map, the country is depressed to about 4,500 feet, yet the Pliocene 
beds occupy the entire area. As the Miocene and Pliocene are conform- 
able, so far as angle goes, the absence of the Miocene in the northeast 
corner of the map is evidence of a depression in that region since the depo- 
sition of the Pliocene. 

When examined on a north-and-south line, the surface of the Plains is 
a series of gentle undulations, rising to the greatest height between streams. 
Each stream which is traced from west to east across the plain occupies a 
sharp valley, usually walled in upon either side by abrupt bluffs, the top of 
the bluffs representing a general depression considerably lower than the 
table-lands between the streams. In other words, the present sharp, cation- 
like valleys are eroded in the bottom of a previously carved broad, gentle 
valley. The average grade of these streams, from the mountain base to the 


PLIOCENE TERTIARY. 427 


eastern edge of our map, is from twenty to thirty feet to the mile. The 
Pliocene strata, it is evident, incline eastward at about the angle of the sur- 
face of the plain. 

Far to the east and north in the valley of White River, and also 
upon Loup Fork, in Nebraska, the contact-plane of the Miocene and 
Pliocene is found at an altitude of about 3,000 feet above sea-level, the 
strata there, as well as upon our area, being apparently horizontal. Their 
deflection from the horizontal is not to be measured by any angular 
observations, but only by observing a given datum-plane over considerable 
east-and-west areas. If the Pliocene strata were truly horizontal in our 
area, and continued so over the whole plains, we should be at a loss for the 
eastward barrier which formerly retained the waters of the lake; but the 
gradual sinking to the east of the contact-plane between the conformable 
Miocene and the Pliocene series offers strong evidence of the depression 
of the entire country into an inclined plane since the deposition of the 
Pliocene beds. This is fully confirmed by the dying out of the Pliocene 
strata in Nebraska and Dakota upon the Cretaceous, where the Tertiary 
beds overlap them unconformably at altitudes 4,000 feet below the highest 
Tertiary limits upon our Map I. The conclusion seems irresistible that the 
Pliocene was deposited in a broad lake when the country between the meri- 
dian of 98° and that of 105° constituted a level area; and that altogether 
subsequently to the deposition of the entire Pliocene series, the whole region 
has been either elevated or depressed into the position of a great inclined 
plane, with a difference of 4,000 feet between the eastern and western limits 
of the lake. 

I gladly credit this remarkable discovery to General G. K. Warren, 
who announced it in 1858. Never having seen his statement, I arrived at 
the same conclusion independently. When I verbally communicated to 
General Warren what I supposed to be an original discovery of my own, he 
referred me to the identical conclusion already published by him in the 
annual report of General (then Captain) A. A. Humphreys for the year 1858. 
Warren’s interesting paper, entitled ‘‘ Preliminary Report of Explorations in 
Nebraska and Dakota, in the years 1855-5657,” was reprinted in 1875. 


From the position of the fresh-water Pliocene beds in Texas, and their 


428 SYSTEMATIC GEOLOGY. 


fauna, there is little doubt that they are an extension of this same lake into 
lowlands of Texas, where they are now observed at sea-level. If I am 
right in assuming the probability of these beds constituting a portion of 
one Great Plains Pliocene lake, the depression in a southerly direction 
has been even greater than that along the eastern edge of the lake; and 
the difference of level between our highest observed Pliocene altitude and 
the fresh-water Pliocene of the Texan seaboard would indicate a change 
of level of 7,000 feet. 

The character of these changes of level presents some curious oro- 
graphical considerations. Over this whole area there is nowhere the slight- 
est evidence of either faults of importance or noticeable folds in the Plio- 
cene sediments. Wherever observed, they have the character of horizontal 
beds. We must therefore suppose that either the country to the west and 
north was gradually lifted without fold or fracture, or that the eastern and 
southern margins of the lakes were depressed from 4,000 to 7,000 feet 
without any noticeable local displacements or crumplings within the entire 
area of the lake. This will be particularly alluded to in a subsequent 
chapter on mechanical geology. Our small Fortieth Parallel portion of this 
Pliocene lake, therefore, is to be considered as an area of beds on the 
western elevated edge of an inclined plane. 

Westward of Carr’s Station, along the southern limits of the Pliocene, 
that formation is seen to rest directly upon the Cretaceous, having over- 
lapped the otherwise conformable Miocene. North and west it is seen over- 
lapping all the sedimentary series of Mesozoic and Paleozoic age, in places 
coming directly in contact with the Archaean core of the range. 

As nearly as we can estimate, about 1,500 feet of beds are exposed in 
the series. It will be remembered that the Miocene of Chalk Bluffs was 
described as characterized by beds of marly clay and ferruginous sandy 
clays, the whole remarkably fine-grained and devoid of all broad zones of 
coarse material. The Pliocene, on the other hand, is to be distinguished 
by prevailing sandy formations of great vertical thickness; the predominant 
sandy character of the series being locally interrupted by marls, clays, gritty 
sandstones, some sheets of rather fine conglomerate, and peculiar brittle 


limestones, the latter apparently of no very great geographical extension. 


PLIOCENE TERTIARY. 429 


The more important beds are rather coarse yellowish creamy sandstones, 
whose material is seen to grow coarser in approaching the mountain base, 
until in direct contact with the foot-hills of the range it is decidedly a con- 
glomerate, consisting of pebbles, masses of quartz and feldspar, and chips 
and fragments of all the Archean rocks represented in the crystalline body, 
varying in size from a pea to a pumpkin. These conglomerates form the 
uppermost beds, and when eroded by the mountain streams show finer 
materials immediately underlying them, a peculiarity of erosion along the 
upper waters of the stream being overhanging eaves of harder rocks on the 
bluff edges, under which the softer material has been worn away. Close 
by the mountains these beds dip 14° away from the hills. The conglom- 
erates are in several different layers, the coarsest being in the last bed. In 
passing eastward from the mountains, the pebbles become finer and finer, 
until they are little more than fine, grayish grits. Wherever seen, they are 
underlaid by calcareous grits and fine, whitish marls. 

South of the Union Pacific Railroad, especially south of Otto and Haz- 
ard stations, the Pliocene beds are eroded in a series of rough terraces, 
with angular bastions and sharp escarpments, forms which have given rise 
to the name of “Natural Forts.” 

The surface of the plateau, a few miles south of Cheyenne, and thence 
for a considerable distance eastward, is made up of a bed of light, creamy 
limestone, with a brittle sherdy fracture, and a good many small veins of 
chalcedonic material. An analysis of this limestone will be found in the 
table of stratified rocks 

East of the meridian of Cheyenne, over the broad plains to the north, 
the beds are altogether fine-grained, chiefly arenaceous, but interlaminated 
with a few beds of clay and marl, the prevailing color being pale olive- 
gray. The valleys of Crow, Lodge-Pole, and Horse creeks show a slight 
tendency to bluff formations on their banks, while the Chugwater is bor- 
dered for forty miles with a more continuous line of abrupt cliffs. These 
sharply escarped bluffs are cut at right angles by lateral ravines. As in 
the soft Bridger beds, so among the fine, marly members along the Chug- 
water and other northern valleys, are observed thin lenticular masses of 
jaspery rock, which sometimes carry dendritic infiltrations, resulting in 


430 SYSTEMATIC GEOLOGY. 


moss-agate. Molluscan remains were not found. Fragments of silicified 
branches and trunks of trees abound, but the most important fossil remains 
are those of vertebrates, of which large numbers were obtained from Chalk 
Bluffs. The most important forms from this lake are— 


PLIOCENE OF THE PLAINS. 
Canis sevus, Leidy. 
Canis temerarius, Leidy. 
Leptarchis primus, Leidy. 
Cervus Warreni, Leidy. 
Merychyus elegans, Leidy. 
Procamelus robustus, Leidy. 
Megalomeryx Niobrarensis, Leidy. ° 
Merycodus necatus, Leidy. 
Cosoryx furcatus, Leidy. 
Platygonus striatus, Marsh. 
Bison Alleni, Marsh. 
Bison ferox, Marsh. 
Tapiravus rarus, Marsh. 
Protohippus parvulus, Marsh. 
Protohippus perditus, Leidy. 
Protohippus placidus, Leidy. 
Protohippus supremus, Leidy. 
Plohippus pernix, Marsh. 
Pliohippus robustus, Marsh. 
Merychippus insignis, Leidy. 
Merychippus mirabilis, Leidy. 
Hystrix venustus, Leidy. 
Arctomys vitus, Marsh. 
Geomys bisulcatus, Marsh. 
Moropus elatus, Marsh. 
Grus Haydeni, Marsh. 
Aquila Dananus, Marsh. 
At three places along the eastern base of Colorado Range are devel- 
opments of coarse, semi-stratified gravels and conglomerates. Along the 


PLIOCENE TERTIARY. 431 


northern line of the map, on the branches of the Sybille, these gravels dis- 
tinctly overlie the Niobrara Pliocene, abutting against the Archzean core 
of the range, from which their material is derived. The same is true of 
the region at the head of Chugwater and Pebble creeks. Apparently the 
same formation recurs in the valley of the Big Thompson, near the southern 
edge of the map, where similar conglomerate table-lands rest upon the Colo- 
rado and Fox Hill Cretaceous. Along the northern part of the map are 
200 or 300 feet of these gravels, which descend toward the north and east 
in rude terraces. They are made up of coarse bowlders and pebbles and 
rough siliceous sand, composed altogether of granitic materials. At Big 
Thompson Creek they form benches or terraces 200 feet above the level of 
the stream, leaving to the east of the main body a few isolated outliers, 
which have successfully resisted erosion. At the latter locality, bowlders 
of Triassic sandstone mingle with the Archzan material of the con- 
glomerates. 

These southern bodies, taken by themselves, might possibly be con- 
sidered as relics of the age of the great Pliocene beds which abut against 
the foot-hills, since they rest directly on the Cretaceous. But taken in con- 
nection with the developments to the north, it is most probable that they 
post-date the Niobrara Pliocene. I have placed this group as the closing 
member of the Tertiary series for the following reasons: It clearly over- 
lies the Niobrara Pliocene, and it is absolutely certain that it antedates 
the Glacial Period, and consequently the gravel deposits of the Quaternary. 
While the Pliocene formations of the Plains abut directly against Colo- 
rado Range, the other side, flanked by the broad Cretaceous depression of 
the Laramie Plains, is altogether free from the Tertiary. Its altitude is 
about 7,000 feet, which represents the highest limits to which the Pliocene 
reached on the eastern side of the range. It is therefore probable that the 
range itself formed in these latitudes the westward barrier of the Pliocene 
lake. 

Nortu Park Grour.—West of the western base of Medicine Bow 
Range the depression of the North Park, surrounded by bold Archean 
masses on the north, east, and west, and separated from the similar 
depression of Middle Park by upheaved Cretaceous rocks and high ridges 


432 SYSTEMATIC GEOLOGY. 


of voleanic material, was occupied by a lake which we have every reason 
to believe was of Pliocene date. The entire valley of North Park, except 
where the Cretaceous and voleanic rocks rise above its surface, is occupied 
by a nearly horizontal set of lacustrine strata, which in places overlap the 
secondary beds and come directly in contact with the Archzean bodies. 
The materials near the contact are composed of detritus of Archzean schists, 
and granitoid rocks of comparatively coarse sizes. Where it overlaps the 
softer shales of the Cretaceous, however, it is made up of the rearranged 
débris of those rocks. In general, therefore, the exterior boundaries of 
this oval basin of Tertiaries are varied in coarseness and texture. The 
entire middle portion of the park, however, is covered with horizontal beds 
of extremely white, fine, marly and sandy deposits. The various affluents 
of Platte River have eroded shallow valleys through these soft beds, dis- 
playing along their banks many excellent sections. There seem to be not 
over 300 feet of these materials. 

Made up as they are of local débris from the surrounding hills, and 
devoid, so far as our observations go, of fossils, it is difficult to cor- 
relate these beds with other formations. They appear to occupy, never- 
theless, positions entirely similar to the Niobrara Pliocene to the east, and 
may hereafter be proved by fossil remains to be the equivalent of those 
beds. In the absence of proper evidence, we have simply made of them a 
special group, calling it, after the locality of the basin, the North Park 
group. That they are Tertiary, is clear from their position unconformably 
over the Cretaceous. That they are Pliocene is rendered highly probable 
by their abutting horizontally against the post-Cretaceous basaltic hills 
which line the park at the southwest. In these so-called Pliocene North 
Park beds we find no basaltic tuffs, such as are intercalated in a lacustrine 
series in the Middle Park. 

Among the loose, friable sandstones are soft whitish and grayish- 
white and buff marls, which cannot be distinguished from the Niobrara 
Pliocene of Horse Creek. Not a small portion of the material of the beds 
has been derived from trachytic and rhyolitic rocks which, in enormous 
masses, bound these Tertiaries to the south and east. 

A continuation of this lacustrine Pliocene occupies the whole valley 


PLIOCENE TERTIARY. 433 


of the North Platte, up to the latitude of 41° 30’. Throughout that 
distance it rests directly upon the Archean rocks on both sides of the 
vailey, wrapping around the northern end of the Grand Encampment 
Mountains, and extending out unconformably upon the Laramie Creta- 
ceous to the west of Savory Plateau. Here are exposed in all about 1,000 
feet of rocks, which on the south of Bruin Peak reach an altitude of not 
less than 8,800 feet above sea-level, and again at Savory Plateau about 
8,500 feet. The highest of the Pliocene deposits within the valley of 
North Park cannot fall far short of these figures, which probably represent 
the upper limit of the lake. 

As developed in the valley of the North Platte, the group is composed 
chiefly of sandstones of varying coarseness, capped by about 300 feet of 
drab, marly limestone, which near the Archean shore of the lake contains 
small pebbles. The lower beds, as displayed upon Jack’s Creek, include 
strata of indurated clay, containing fine pebbles and some plates of brown 
and white mica. West of Savory Plateau and south of Little Muddy 
Creek, the limits of this Tertiary are not definitely known, since the area 
is covered with much soil and dunes of sand, the latter urged eastward by 
the prevalent west winds of the region. It was therefore impossible to 
determine the relation between the North Park group and the Vermilion 
Creek group west of the belt of Laramie Cretaceous. 

It has sometimes seemed possible that this great thickness of North 
Park Tertiary might possibly be an eastward extension of the Eocene 
basin, whose limits approach it so nearly in the region of Savory Plateau; 
but if, as we have supposed, the basalts of the southern end of North Park 
are coeval with those of the Elk Head Mountains, it is clear that the 
two Tertiaries sustain different relations to their eruption. The wonderful 
dike which rises above the Vermilion Creek strata west of the Elk Head 
Mountains, to which Mr. Emmons has given the name of the Rampart, 
clearly cuts through the soft Eocene beds, while it is equally certain that 
the Tertiaries of the northwest corner of North Park abut unconformably 
upon the flanks of the basaltic hills. 

There are some slight indications, especially near the three forks of the 


Platte, at the north end of the depression of North Park, of a disturbed 
28 K 


434 SYSTEMATIC GEOLOGY. 


Tertiary, which is possibly unconformable beneath the light beds that 
cover the main surface of the Park. 

The peculiar northern termination of this series of Tertiary rocks in 
the region of Savory Plateau and the Platte valley has left their former 
extension as a difficult problem. There seems to have been no barrier 
which should have prevented the northward continuation of these Tertiaries. 
Nor do the Cretaceous rocks west of Savory Plateau at present afford a 
sufficient topographical altitude to wall in a Pliocene lake in that direction. 
These difficulties have sometimes suggested that possibly the main Tertiary 
of the North Platte valley might in some way be an eastward extension 
of the Eocene itself, and the calcareous upper rocks which are seen within 
the Platte valley might be correlated with the calcareous lower Green 
River beds. We did not, however, detect any break between the rocks of 
the Platte valley and those of North Park which are unconformably above 
the basalt, and hence the whole series are provisionally referred as one 
group and placed within the Pliocene, and I shall be quite ready to welcome 
any additional evidence on the subject. 

The angular discrepancy with the Cretaceous rocks west and south of 
Savory Plateau is very slight, but north, where it overlooks the valley of 
Sage Creek, the discrepancy is undoubted. There the uppermost member 
is a hard, siliceous shale, underlaid by white, limy sandstones. 

Much of the valley of the Platte is covered by accumulations of Quater- 
nary material, but the Tertiary beds may be followed nearly uninterrupt- 
edly along the northern flanks of Grand Encampment Mountain and Pel- 
ham Peak. The overlying Wyoming conglomerate of Savory Plateau 
offers no proof as to the age of these Tertiaries, since it sustains the same 
position as has been observed over the Eocene beds to the west, and over 
the Niobrara Pliocene along the eastern base of Colorado Range. 

Humpotpr Grour.—The whole subject of the Tertiaries of the basin 
of Utah is surrounded with unusual difficulty. Along the western base of 
the Wahsatch, a portion of the Terrace country, rising to 700 or 800 feet 
above the level of the lake, is composed of loose, friable Tertiaries, carry- 
ing very recent fresh-water mollusks, the genera at least being chiefly the 


equivalents of existing types. These beds along the western base of the 


PLIOCENE TERTIARY. 435 


Wahsatch are approximately horizontal. Three considerable depressions 
east of the main ridge of the Wahsatech—Morgan, Cache, and Ogden 
valleys—which unquestionably represent bays formerly connected with 
the main Pliocene lake west of the Wahsatch, have been the receptacles 
of Pliocene sediments very similar to the fragments of horizontal Pliocene 
terraces on the west base of the Wahsatch. They are all characterized by 
recent genera of fresh-water mollusks. The height of the Tertiary in all 
these valleys reaches a full thousand feet above the level of Salt Lake. 

With the exception of terrace-masses along the western base of the 
Wahsatch, which for the most part are deeply covered by Quaternary deposits, 
the valley of Salt Lake carries a sheet of Quaternary, through which rise 
masses of Palaeozoic and voleanic rocks. The northern boundary of this great 
basin is beyond the limits of our map, but has been crossed by us in several 
places, and the members of the Exploration have been unanimous in refer- 
ring to the Pliocene period a considerable series of horizontal rocks which 
occupy a divide between the waters of the Utah Basin and those of Snake 
Valley. These rocks are composed chiefly of friable gray, white, and drab 
sandstones and marly limestones, for the most part horizontal, but in places 
uplifted at low angles. At the northwest boundary of the Salt Lake Basin, 
near the 114th meridian, at latitude 40°, are further exposures of horizontal 
Pliocene rocks, which rise to altitudes of 1,000 to 1,800 feet above the 
level of the Basin. 

The question naturally presents itself, Why are not these beds contin- 
uous over the whole Salt Lake Basin? If eroded away, by what channel 
could the enormous amount of material have been conducted beyond the 
limits of the enclosed basin? It is unquestionably to-day a restricted basin, 
from which no water escapes. Its boundaries are nowhere less, so far 
as we know, than 600 feet above the present level of the lake; and since 
the Tertiaries to the north form a barrier, how is it possible that 1,000 or 
2,000 feet of Tertiary material can have been removed from the whole 
area of the basin, there being no channel through which it could have 
been transported? There is one hypothesis which accounts for these 
curious facts. If after the deposition of the Pliocene lacustrine beds the old 
fault which had been previously defined along the whole west base of Wah- 


436 SYSTEMATIC GEOLOGY. 


satch Range were again to become the theatre of displacement, and what is 
now the valley of Salt Lake were to suffer depression, a basin might be 
formed of sufficient depth to act as a receptacle for the detritus derived from 
the surrounding Tertiaries. That this has actually occurred, there can 
be no doubt. The horizontal beds which are now reposing against the 
western flank of the Raft River Mountains, the similar body lying west of 
Deep Creek Valley being supposed to represent a comparatively undis- 
turbed portion of the series, have their easternmost correlatives in Cache 
Valley, Ogden Valley, and Morgan Valley, while the intermediate area 
has suffered a depression greatest along the actual western base of the 
Wahsatch. 

The Tertiary beds of Cache Valley consist of grayish sandstone and 
marly limestone, presenting a great variety of size of grain, some of the 
beds being excessively coarse, porous sandstones. Among the limy beds, 
some are essentially odlitic; others are made up almost entirely of late 
Pliocene fossil shells, among which Meek recognized a new Lymnea. 

The Quaternary terraces of Bonneville Lake, which will be described 
in the succeeding section, cover and obscure much of the Cache Valley 
Pliocene, but enough is laid bare to indicate positively about 400 feet of 
beds, and probably as much as 700. Near the northern end of the valley, 
not far from the town of Mendon, they are considerably disturbed, showing 
angles of 10°, and even 15°. Along the whole flanks of the valley these 
Pliocene rocks rest nonconformably upon the immense masses of limestone 
of the surrounding mountains, and at the contact are usually obscured by 
mountain débris. A few of the beds are compact enough to have been used 
for building-stone. . 

Along the southern part of the valley a prominent red sandstone is 
observed, underlaid by lavender calcareous sandstones. Near Mendon, 
LTymnea and Helix abound in the sandstone. 

Ogden Valley, a depressed area walled in by high mountains and dis- 
charging its drainage through the cation of Ogden River into the valley 
of Salt Lake, was also an enclosed bay in the Pliocene lake. Wherever 
the important surface-accumulations of Quaternary gravels and earth have 
been washed away, sandstones similar to those of Cache Valley are seen. 


PLIOCENE TERTIARY. 437 


The Pliocenes are here obscured by the same Bonneville Lake terraces as 
in Cache Valley. 

Morgan Valley is the third of these interior Pliocene bays, whose de- 
posits do not greatly differ from those of Ogden Valley, except in being 
rather finer and whiter. No molluscan remains were observed here. 

The limestone mass of Terrace Mountain, on the northwestern margin 
of the Utah Basin, is divided by a northwest-and-southeast depression, which 
severs the range into two equal portions. Upon the eastern and western 
sides the depressions of this pass form bays in the limestone which are occu- 
pied up to a thousand feet above the lake-level by horizontal Pliocene, con- 
sisting of fine yellowish and whitish sands, reddish gravels, and marly 
sands, all very loosely compacted, but nevertheless unmistakably a Tertiary 
formation, and in nowise to be confounded with the Quaternary marls of 
the desert. These fragmentary remains are of no little importance, since 
they present their escarped and bevelled edges horizontally, and attract 
marked attention to the absence of the extensions of the beds in the sur- 
rounding country 

A similar but geographically much more important area is exposed 
along the western side of the Raft River Mountains, in the northwestern 
corner of Map III. Here the entire western base of the high limestone 
range is buried under soft, white, friable sandstones, conglomerates, and 
pumiceous tuffs, which rest in complete horizontality, and are exposed for 
a thickness of probably 1,000 feet. This is only another of the detached 
relics which have escaped depression and erosion. 

In the southeastern corner of Map IV. the broad Quaternary valley of 
Deep Creek is flanked upon the west by low, softly sloping hills, which rise 
about 1,000 feet above the valley. The exposure for a distance of twenty- 
five miles north-and-south by six or seven miles transversely is entirely of 
fine white sands and marls, with a few rather fine gravelly conglomerates 
unquestionably referable to the Pliocene age. One particular bed is con- 
spicuous for its very rough texture; it is a rearranged volcanic ash, similar 
to those found in the region of Toano. 

There is a particularly large development of undisturbed Pliocene, not 


less than 500 or 600 feet in thickness, on the divide between ‘Thousand 


438 SYSTEMATIC GEOLOGY. 


Spring Valley and Holmes Creek. The upper bed of this exposure is a 
drab, earthy limestone, full of siliceous and muddy impurities, and peculiar 
from the number of ferruginous dendritic infiltrations. The greater part of 
the Holmes Creek beds are originally due to volcanic eruptions. Geog- 
nostically they do not very greatly differ from the trachyte lacustrine 
tuffs of the western Miocene beds, and, like these, they are formed of the 
sands and rapilli of a direct ejection. They are, however, the tuffs of Pli- 
ocene rhyolite eruptions. The escarpment of these pumiceous Pliocenes 
results in interesting castellated forms; a fine sample on the eastern side of 
the valley has received the name of Citadel Cliff, from its bold architectural 
form. Here are exposed over 100 feet of evenly bedded white sands, con- 
taining many small, transparent glass particles. 

Among the beds of volcanic derivation is a noticeable stratum, having 
a thickness of about five feet, formed of closely compacted fragments 
of brown, glassy material. The microscope shows it to be made up of 
erystals of feldspar and quartz in a groundmass of red and black voleanic 
ash, the red particles being a rhyolitic glass, and the black particles a pure, 
true black obsidian. The upper bed of the surface of Citadel Cliff is made 
up of cream-colored conglomerate, in which lime is a large element. 
Between Thousand Spring and Gosiute valleys, and throughout the entire 
western slope of Toano Pass, similar horizontal beds of rearranged sand 
and volcanic material occupy the rolling country. They overlie the up- 
turned Eocene of Peoquop Pass with clear nonconformity. Near the town 
of Toano a peculiar solid white pumiceous bed is found to be admirably 
adapted to building-purposes, since it is very easily quarried, and hardens 
upon exposure. 

West of Humboldt and Tucubits ranges there is a long valley 
drained by Humboldt River and Huntington Creek. Throughout the 
length of this depression, over 100 miles, there is a nearly continuous 
exposure of horizontal Pliocene beds. It is difficult to decide what thick- 
ness of beds is exposed, since they are often buried by Quaternary, but 
there cannot be less than 600 or 800 feet. In the middle of this valley the 
beds are horizontal, but on either side there is-a dip of from 2° to 3°, which 
is probably the inclination of deposition. The foot-hills of the ranges on 


PLIOCENE TERTIARY. 439 


both sides are skirted by continuous belts of Tertiary, which are bevelled 
off to the central valley. Streams have excavated broad depressions down 
these plains, and the intervening spurs have been graded off so that the 
whole valley country presents few abrupt exposures, and those only along 
certain exceptionally sharp stream-cuts. The most important of these are 
seen in the valley of the South Fork of the Humboldt, where 100 to 150 
feet of sandstone cliffs flank the valley on either side. Here are found 
sands, that are at times quite marly, associated with more or less coarse 
beds of grit, which nearer the mountains are entitled to be named conglom- 
erate. There are a few calcareous clays and some limited beds of true 
marly limestone. It is not surprising that this whole Pliocene exposure 
should have more or less calcareous material within its mass, since so large 
a portion of the surrounding mountain-sides from which the material has 
been derived is of Palaeozoic limestones. 

A little north of Pinon Pass, on the western side of Pinon Range, is 
an exposure of about 80 or 100 feet of highly calcareous horizontal beds. 
The spurs and hills resemble white chalk, or white, infusorial silica. Cer- 
tain of the porous beds are impregnated with alkaline carbonates, as if the 
lake in which they were formed had been saline, or, as is possibly though 
not probably the case, they had suffered alkaline infiltrations in more mod- 
ern times. Similar deposits fill the valley north and south of the Hum- 
boldt as far west as the meridian of 116° 45’. 

There is little doubt that all these exposures of Pliocene represent the 
deposits of one lake, out of which the numerous lofty mountain masses 
were lifted in a complicated system of islands. Fossil remains are exces- 
sively rare, for the reason that the greater part of the area which is colored 
as Tertiary is overlaid by more or less Quaternary débris. At Bone Valley, 
which is drained by the waters of the North Fork of the Humboldt, a few 
vertebrate remains were found, including a jaw of Protohippus perditus, also 
a jaw of Merychippus mirabilis, and fragments of Cosoryx. These forms are 
of exceeding importance as proving the identity of the beds in which they 
were found with those of the Niobrara Pliocene east of the Rocky Moun- 
tains. 


A similar proof has been obtained by Professor Marsh as to the Plio- 
y 


440 SYSTEMATIC GEOLOGY. 


cene beds of Oregon, and but one reason has restrained us from coloring 
all the Tertiaries west of the Walhsatch as Niobrara. It is, that in the 
great Boise Basin, which is drained by Snake River, and which lies directly 
north of the region that has just been described, there are two sets of Plio- 
cene strata, separated by basaltic eruptions. Sections obtained along the 
plains between the Owyhee Mountains and Snake River show that a con- 
siderable portion of the beds of the valley, which consist chiefly of 
white sands and marls carrying numerous well defined Pliocene forms, 
were overlaid by large accumulations of basaltic flow, and that subsequently 
a second period of lacustrine deposition took place, likewise characterized 
by Pliocene forms, the latter representing a more advanced stage of devel- 
opment and more recent type than those beneath the basalt. The Nevada 
and Utah Pliocenes carry few organic remains. Later, it will be evident 
that either basaltic outflows lingered later in Idaho or else the greater part 
of the western Nevada Pliocene is the equivalent of the post-basaltic Idaho 
series. 

It is unnecessary for our present purposes to follow the details of the 
Pliocene outcrops over the remaining part of Map IV. and those which 
occur on Map V. Their character is that of soft, partially compacted, 
locally derived material, laid down in a series of intricate valleys, winding 
among what at the time of deposition were islands of the most complicated 
geological structure. The beds which are seen along Humboldt River 
show a maximum exposure of about 3800 feet, of which white and creamy 
varying sands, a few beds of pale-yellowish clay, and a little conglomerate 
are all that appears. The Humboldt Valley south of its bend at Lassen’s 
Meadows cuts a canon through these Pliocene strata for about twenty-five 
miles, exposing cliffs upon either river bank from 150 to 300 feet high. 
No fossils were obtained, except near the northern end of Havallah Range, 
where portions of the skeleton of a Pliocene equine animal were exhumed ; 
and near Mill City, in the excavation of a mining canal, numerous Pliocene 
Unionidae were obtained. 

Similar to the exposures along the valley of the Humboldt are those 
exposed in the ecafion of the Truckee, south of Wadsworth. This river, 


after traversing its sinuous canon across Virginia Range, suddenly turns 


PLIOCENE TERTIARY. 44] 


to a northwest direction and enters a cation from 100 to 200 feet deep 
through horizontal beds of soft, white, marly sands, and fine arenaceous 
and clayey beds, mingled with coarse, almost conglomeratie grits. 

By far the most important question connected with these western Plio- 
cene beds is that which has already been discussed in the department of 
the Plains and in the basin of Salt Lake, namely, the orographic movements 
which their position proves. 

One cannot fail to ask, What has been the probable connection, over 
this whole area of middle and western Nevada, of the Pliocene beds? 
Wherever the Quaternary has by any accident failed to cover valley 
areas, we immediately come upon strata of Humboldt Pliocene. There 
is little doubt that if the entire Quaternary were removed from the region 
it would be seen to be blanketed with a stretch of Pliocene beds, uninter- 
rupted except by the mass of the older mountains. Passing westward from 
the region of Toano, where the altitude of these horizontal beds is about 
6,000 feet, they may be traced with no interruption, at least with no bar- 
riers to prevent their continuation, westward down the valley of the Hum- 
boldt and throughout all the complicated net-work of valleys which commu- 
nicate with the level of the Pliocene beds, gradually sinking as we progress, 
until in the region of Pyramid and Winnemucca lakes they are at an alti- 
tude of about 3,800 feet above the sea. 

We are forced to admit either that there was a series of communicating 
lakes which drained to the west, the lowest member of the chain being 
along the depressed western edge of Nevada, or else that all these Pliocene 
beds represent the deposits of one intricate lake which subsequent to Plio- 
cene time has been depressed westward, making a difference of elevation of 
2,000 feet between its eastern and western edges. The problem reduced 
to that form, if answered by the hypothesis of a series of different Pliocene 
lakes, varying from 4,000 to 6,000 feet above sea-level, resolves itself into 
a still more difficult one. We to-day find the horizontal Pliocene beds along 
Truckee River lying at altitudes above Pyramid Lake, into which the waters 
of the Truckee flow. All the modern drainage of a wide area flows into the 
depressed region occupied by Pyramid, Winnemucca, Carson, and Walker's 
lakes, the present levels of these lakes being all under 4,000 feet. 


442 SYSTEMATIC GEOLOGY. 


The Quaternary detritus, therefore, from the Pliocene beds which we 
find within this drainage-area at an elevation of 6,000 feet along the upper 
Humboldt Valley, must be and must have been delivered into the lowest 
part of the basin; and if that were the case, it is inconceivable that the Pli- 
ocene beds of Truckee River should have remained unburied by modern 
detritus. Pyramid Lake itself has its bed several hundred feet below the 
neighboring Pliocene beds, and it is over 2,000 feet below the apparently 
horizontal beds in the upper valley of the Humboldt. The only possible 
way of accounting for this relation is to suppose that the whole country 
from about the meridian of 114° 30’ was depressed to the west, the western 
edge of the lake settling 2,000 feet. If, as we believe, there is no proof 
whatever against the continuity of the Pliocene sediments from Thousand 
Spring Valley westward to Pyramid Lake, the same is true from that point 
eastward to the deposits of Cache Valley. I believe that the entire section 
of Utah and Nevada studied by us was covered by one Pliocene lake, in 
which the series of parallel ranges was an archipelago, and that in post- 
Pliocene times a very great orographical movement has taken place, the 
maximum displacements being upon two lines: one upon the eastern base 
of the Sierra Nevada, a region of long previously defined fault, the other 
upon the western base of the Wahsatch, also a region of recurrent faults. 

There is, according to this view of the case, a comparatively undis- 
turbed region in the neighborhood of Thousand Spring Valley, from which 
the Tertiaries to the east have sunk in an inclined plane as far as the 
base of the Wahsatch, where they were carried to a considerable depth 
below the present surface, making a displacement of over 1,000 feet. 
Westward they have sunk in another inclined plane to the base of the 
Sierra Nevada, where the displacement was certainly 2,000 feet. The 
throwing of the horizontal deposits of this broad lake into two inclined 
planes has been of the same gentle character as that already described upon 
the Great Plains. In the case of the displacement which occurred along 
the base of the Wahsatch, we have corroborative evidence in the upturned 
position of the Tertiaries along the divide between the basin of Salt Lake 
and that of Snake River; also at the northern end of Cache Valley, a 
region which must have been closely contiguous to the plane of displace- 


PLIOCENE TERTIARY. 443 


ment. In both these places the Pliocene beds are upturned at angles from 
10° to 20°, a phenomenon not elsewhere observed by us, but one which 
finds its counterpart in the post-Pliocene coast rocks of California, where 
a series of intense, recent orographical disturbances has been brought to 
light by Professor Whitney. As horizontal Pliocenes occur upon the divide 
between the basin of Utah and that of Idaho, it becomes quite certain 
that during the Pliocene the two areas were regularly connected as one and 
the same lake. 

As between the basin of Idaho and that of eastern Oregon, the 
connection is not so clear; but between western Nevada and Oregon it is 
evident that the Pliocene beds carry over from one to the other, and it 
will not be at all surprising if future work demonstrates that in Pliocene 
times Utah, Nevada, Idaho, and Oregon were in part covered by one and 
the same great Pliocene lake, studded with numerous mountainous islands. 
I consider it proved that the displacement at the Sierra Nevada base and 
the Wahsatch base were at the close of the Pliocene, and thus broke the 
one broad lacustrine basin into two new lake basins—one at the foot of the 
Sierras, the other under the shadow of the Wahsatch Range—which were 
to receive the waters of the Quaternary age, and form lakes whose exist- 
ence will be discussed in the next section. The following are the more 
important fossils described by Prof. O. C. Marsh from the Pliocene beds of 
the western lake: 


Platygonus Condoni, Marsh. 
Dicotyles hesperius, Marsh. 
Anchippus brevidens, Marsh. 
Protohippus avus, Marsh. 
Morotherium gigas, Marsh. 
Morotherium leptonyx, Marsh. 
Graculus Idahoensis, Marsh. 
Ehinoceros Oregonensis, Marsh. 


SE Cr LONm ny: 
RECAPITULATION OF TERTIARY LAKES. 


The relations which subsist between the Laramie Cretaceous and the 
Vermilion Creek or lowest Eocene group have been stated in a general 
way in the Mesozoic chapter, and the fuller evidence of the nonconformity 
there asserted was presented when discussing Eocene geology. I shall 
now, by way of recapitulation, outline as succinctly as I am able the 
remarkable sequence of lacustrine Tertiary basins which since the close of 
the Laramie period have played so important a part in the geology of the 
middle Cordilleras. 

I have shown that in the region east of the Wahsatch the great series 
of conformable strata was a periodically subsiding series, having the greatest 
amount of post-Carboniferous sinking near the Wahsatch or western shore. 
The sediments which overlay the depressed parts of the Rocky Mountain 
chain and encircled its rugged islands were thinner than at the Wahsatch 
region, but at the close of the Cretaceous were equally near the ocean 
surface, as is indicated by the abundant series of coal-beds in the upper 
Laramie. I may anticipate an important observation from a subsequent 
chapter on the mechanical disturbances of the middle Cordilleras by saying 
that, in very many instances, the subjacent Archean topography has 
exerted a marked influence on subsequent disturbance; indeed, it has 
evidently determined the loci of most modern ranges. 

An important instance is the post-Cretaceous tilting of all the conform- 
able post-Archzean beds up to the top of the Laramie, over and around the 
Rocky Mountain islands and submerged ranges. 

At the close of Cretaceous time the relative upheaval of the whole 
Rocky Mountain chain and the west shore of the Cretaceous sea, including 
the system of the Wahsatch and its northerly extension, resulted in the wall- 
ing in of the system of the Colorado River, which then for the first time 


became an area from which the sea was quite excluded. The Wahsatch 
444 


RECAPITULATION OF TERTIARY LAKES. 445 


and Rocky Mountain systems, passing northward, trended together, meeting 
near the present head waters of Green River; southward they diverged 
more and more, until in New Mexico and southern Colorado the two walls 
of the basin are five hundred miles apart. 

Over a considerable portion of this enclosed area, the then latest rocks, 
the Laramie, were left either horizontal or in gentle folds. Exceptions to 
this in the area of the Fortieth Parallel were Uinta Range and its easterly 
dependencies, Oyster Ridge, Bitter Creek quaquaversal, and other lesser 
folds. As a whole, it was an enclosed basin, secluded from any marine 
invasion. 

Littoral and estuarial faun, together with the Dinosaurians, perished 
with the revolution which created this basin. 

Fresh water from the surrounding and inwardly draining area rapidly 
converted the basin into a sweet lake, having a drainage southward to the 
sea. Whatever ocean waters may have been caught in the hollow land 
were at once diluted and flooded out, as is evidenced by characteristic 
fresh-water fauna entombed in the sediments of the lake. 

For this body of water I propose the name of Urr Lake, taking the 
name of an Indian tribe whose roaming-ground covers a large part of the 
lake area. It has fallen to our corps to study only that portion of the lake 
lying north of the 40th parallel. 

Above that latitude it filled the entire Green River Basin for a distance 
of one hundred and fifty miles north, with an east-and-west exposure of 
about the same distance on the parallel. It is expected that the labors of 
Hayden, Powell, and Gilbert will outline its southward continuation and 
complete its ancient shore line. Already, from a locality in New Mexico 
over two hundred miles south of our work, Marsh has reported represen- 
tatives of the fauna of this lake, and it only remains to be proved, as will 
be easily done, whether Ute Lake actually extended so far south, or 
whether, as is at present wholly improbable, it was succeeded in that direc- 
tion by another lake of the same age and faunal characteristics. 

The deposits of Ute Lake are the beds of the Vermilion Creek group, 
already shown to be of basal Eocene horizon, a series having in our field 
a maximum thickness of about 5,000 feet, and carrying, besides abundant 


446 SYSTEMATIC GEOLOGY. 


fresh-water mollusca and a few fishes, the characteristic vertebrate fauna of 
the lowest Eocene. 

The entire group of beds is made up of predominant sandstones, 
which carry conglomerates along the shores and hold minor clay intercala- 
tions. The prevailing color is red, the clays which give character to the 
color being frequently almost vermilion. A few beds of earthy semi- 
lignite give evidence of temporary land-surfaces. The prevailing type 
of sediments is coarse. By far the greater bulk of the material in 
the Fortieth Parallel region came from the land lying west of the lake 
and the lofty Uinta Range, which during the Ute Lake period was an 
island but little detached at its western extremity from the western main- 
land. 

After the accumulation of the Vermilion Creek series was complete, the 
greater supply having come from the high land west of the lake, a period 
of orographic disturbance ensued by which a portion of the western land 
suffered subsidence, and the lake immediately enlarged itself by overflow- 
ing the newly depressed area, thus fully doubling the east-and-west dimen- 
sions. Judging by the sediments of the enlarged lake, the eastern bound- 
ary was also somewhat depressed and the area of the basin somewhat 
increased in that direction. This eastward growth does not show in the 
Fortieth Parallel area, unless the obscure lower Tertiaries of North Park 
and North Platte valleys shall finally appear to be an eastward extension 
of Eocene beds; but it is shown in the beds of Green River Eocene discov- 
ered by Hayden’s survey of the Middle Park. Westward the new lake 
extended to longitude 116°. 

The Uinta was still a great island, and the highland of the Wahsatch and 
its adjoining plateau of lately elevated Vermilion Creek rocks formed a 
peninsula. 

For this new body of water I propose the name of GosruTE Lake. 

In the orographic movements which thus defined a new lacustrine 
basin, the Vermilion Creek rocks over the Fortieth Parallel area were very 
generally disturbed. Along the east base of the Wahsatch they were tilted to 
14°, and on the Uinta western flank to much higher angles. Consequently 
the sediments of Gosiute Lake—the Green River group—were laid down 


RECAPITULATION OF TERTIARY LAKES. 447 


unconformable to the preceding Vermilion Creek group, as is abundantly 
proven in preceding pages of this chapter. 

As developed at characteristic localities in the neighborhood of Green 
River, this group embraces about 2,000 feet of conformable, fine-grained 
rocks, giving general evidence of accumulation in still, rather deep 
water. The lower 1,200 feet are made up of finely fissile shales and 
calcareous clays, with some quite fine limestone. Many of the upper 
shales are strongly bituminous. This member carries numerous fishes 
(already mentioned), many insects, and abundance of fresh-water mol- 
lusks of the genera Viviparus, Goniobasis, and Unio, besides a few beds 
of lignite. 

In the Green River Basin the position of these beds is either nearly 
horizontal or locally upturned to angles up to 25°. In Utah and Nevada 
the outcrops are all isolated exposures which the general Quaternary and 
wide-spread volcanic formations have failed to cover. The rocks are gen- 
erally fine shales, clayey or calcareous, with abundance of carbonaceous 
shale and beds of lignite. The fossil fish, insects, and mollusks are iden- 
tical with those of the Green River Basin. 

Overlying the shales in both the Green River Basin and Nevada are 
heavy beds of ferruginous sandstone, at least 500 feet thick in Wyoming and 
probably much more in Nevada. 

On the mode of extinction of the middle Eocene Gosiute Lake our 
Exploration throws but little light. The only facts in evidence are the slight 
nonconformity in Wyoming between the Green River and the overlying 
Bridger group, and the entire absence of the latter group over the Eocene 
area of western Utah and Nevada. The nonconformity, although slight, 
is sufficient to prove orographical movement at the close of the Green River 
age; and the absence of Bridger beds west of Bear River is very good 
negative proof that the disturbances lifted that region above the Gosiute 
Lake level. In this connection it is of interest to note that the third basin 
thus formed was in the Fortieth Parallel area, wholly within the boundaries 
of the earliest Eocene (Ute) lake. 

For this third Eocene sheet of water I propose the name of WAsHAKIE 
Lake. 


448 SYSTEMATIC GEOLOGY. 


Of the geographical extent of Washakie Lake very little is certainly 
known. North of Uinta Range the group of Bridger beds, the sediment of 
this lake, extends from the meridian of 107° 45’ to 110° 45’, about one hun- 
dred and fifty miles. The northward extension is not definitely known, but 
the beds have been recognized one hundred and fifty miles farther north on 
the low land lying west of Wind River Range. The continuation of these 
beds still farther south will doubtless be described in the reports of Major 
J. W. Powell, for whose southward tracing of the various Eocene members 
we look with interest. 

On the eastern margin of the Bridger exposure, in the Washakie Basin, 
the fragment of Bridger which has been left by the general erosion of the 
region is bounded in every direction by the underlying and next adjoining 
member, the Green River series. The Bridger beds undoubtedly extended 
far east of their present boundaries, and on the west side of the lake, in the 
region of Bear River, there is little doubt that they also extended some miles 
farther westward. It is true, also, that the uppermost members of this group, 
as represented in the Bridger Basin and the Washakie Basin, do not extend 
up to as high geological horizons as certain beds south of the Uinta in the 
White River valley. Between Bear River and Black’s Fork, on the north 
side of the Uinta, the Bridger beds overlap the Green River and come 
directly into contact with the strata of the Vermilion Creek group. At the 
eastern end of the Uinta, where the O-wi-yu-kuts Plateau breaks down 
and sinks beneath the rolling Tertiary plains, a fragment of the Bridger beds 
caps the Green River at such an altitude that its southward continuation 
can hardly be doubted. 

These three Eocene lakes, whose sediments are superposed in the order 
that I have described, buried the flanks of the Uinta island deeper and 
deeper. Yet in passing westward the two upper members give out uncon- 
formably against the Vermilion Creek ridge. It is therefore evident that, 
during the successive depositions of the three lakes, the eastern end of 
Uinta Range suffered a more considerable subsidence than occurred at the 
western end. 

As described in a former section, the rocks of the Bridger group con- 
sist of a conformable series about 2,500 feet in thickness, the lower portion 


RECAPITULATION OF TERTIARY LAKES. 449 


being of drab and gray sandstone with some admixture of clay, the upper 
1,500 feet of a peculiar clay sandstone of olive and drab colors, banded with 
olive-green stripes. From bottom to top they are well charged with verte- 
brate and mollusecan remains; the former distinctly characteristic of the 
middle Eocene age. 

Entirely south of Uinta Range, in altitudes considerably lower than 
the Tertiary Plains north of the range, there is displayed, chiefly in the 
valleys of Green and White rivers, a rather thin group of fine clayey and 
sandy strata, which are apparently unconformable with all other Tertiary 
groups. 

Stratigraphically they are of little interest; their chief importance is 
in the vertebrate fossils, which they yield most abundantly. Professor 
Marsh, who brought this fauna to light, declares positively that it is of 
higher paleontological horizon than the Bridger group and represents the 
summit of the Eocene. Marsh, and Emmons who worked out what we of 
the Exploration know of the stratigraphy of this region, by accident gave 
the same name—Uinta—to the group. 

I therefore propose for the limited body of water within whose area 
the group accumulated, the name of Uinta Lake. 

Evidence of orographical disturbance since the period of Uinta Lake 
is to be found in the drainage of the entire area. It is true that this might 
have been accomplished by the slow wearing down at the point of overflow, 
where a river as yet unproved delivered the surplus water of the lake. 
There is also some evidence of post-Bridger disturbances at the eastern end 
of Uinta Range, where a line of fault has thrown down the beds of the 
Bridger group into contact with the edges of the underlying Green River 
series. The precise mode of the extinction of Uinta Lake remains at 
present problematical; but in the great disturbances which elsewhere 
throughout the Cordilleras are demonstrable as immediately preceding the 
Miocene, there was ample change of level to account for the drainage of 
this lake. That it was extinguished, is rendered certain by the entire ab- 
sence of the Miocene strata over its area; and we are probably within 
the bounds of safety, therefore, in assuming the disappearance of the last 


of the four lakes at the dawn of the Miocene epoch. 
29 kK 


450 SYSTEMATIC GEOLOGY. 


With the exceptions of some peculiar conglomerates, which are believed 
to be of Pliocene age, and the Pliocene reference of the Brown’s Park beds 
by Powell, we have no evidence of Tertiaries subsequent to the deposits of 
the latest Eocene lake within the Fortieth Parallel area between the Wah- 
satch and the Rocky Mountains. 

The faunal equivalents of the four divisions of the Eocene are entirely 
unknown east of the Rocky Mountains, in the great geological province of 
the Plains. There, whenever the covering of Pliocene and Miocene rocks 
which form the main surface of the great inclined plateau is removed by 
the accidents of erosion, they are seen to rest unconformably upon the 
level or gently undulating surface of the Cretaceous strata. There is to- 
day no evidence of the existence of an Eocene lake in the province of the 
Plains. 

It seems, therefore, altogether certain that during the entire Eocene 
age the province of the Plains was a land area having a free drainage to 
the sea. Passing westward from our most western Eocene exposure near 
Elko, Nevada, quite to the west base of the Sierra Nevada, there is also no 
evidence of deposits of Eocene age. Over those portions of western Mon- 
tana, Idaho, and eastern Oregon which have been explored by Whitney, 
Brewer, Gabb, Marsh, and myself, in like manner, no other fresh-water 
Eocene has been observed. It is therefore evident that throughout the 
middle Cordilleras the four lakes described were the only considerable 
regions of Eocene accumulation, and that otherwise during Eocene time, 
from the western base of the Sierra Nevada to the valley of the Mississippi, 
stretched a continuous land area. 

In the orographical disturbance which marked the close of the Eocene, 
two new lacustrine basins of very great extent were created by local sub- 
sidences. The province of the Plains, from somewhere about the north mid- 
dle of Kansas northward far into British Columbia, had its surface at that 
period altogether made up of the eroded level strata of the Cretaceous 
formation. 

At the close of the Eocene a large part of the plains area, from middle 
Kansas indefinitely northward, became depressed and received the drain- 
age which now forms the western affluents of the Mississippi, Missouri, 


RECAPITULATION OF TERTIARY LAKES. 451 


Red River, and other of the British Columbia rivers, forming a wide sheet 
of water. 

For this I propose the name of Stoux Lake. 

Unfortunately the Fortieth Parallel area only covers a very slight 
exposure of the series of Miocene beds which accumulated in Sioux Lake, 
to which, long since, Hayden gave the name of White River group. As 
already shown, it is characterized by typical Miocene fauna. 

The beds, as exposed in our area, are composed of fine clay, sand, and 
marl. On the latitude of 41°, where the Miocene exposures occur with us, 
they rest directly on the gently undulating strata of the Laramie Cretaceous 
series; and it is there evident that the lake did not extend westward quite 
to the present foot-hills of Colorado Range, but had its western shore against 
a low fold of the Laramie Cretaceous. As displayed on the front of the 
Chalk Blufis, the White River Miocene deposits are about 300 feet thick, 
and are overlaid with entire conformity by the coarser sediments of the 
Niobrara Pliocene. The Miocene is never found south of the northern part 
of Kansas, below which point the overlapping sheets of the Pliocene strata 
come in contact with the Cretaceous and prove that Sioux Lake did not 
extend in that direction. The recurrence of the Miocene beds in Manitoba 
indicates a very wide extension of the lake area in that direction. In 
Montana it extended far west of the Black Hills; and, in all probability, its 
deposits form a continuous sheet from latitude 40° and 41° over the whole 
province of the northern Plains. 

The chain of occurrences which ended in the development of a great 
Miocene lake west of the 117th meridian and east of the Sierra Nevada and 
Cascade Range is more obscure than that which brought about Sioux Lake. 
The absence of fresh-water Eocene west of the meridian of 115°, and of 
Cretaceous strata east of the Sierra Nevada, would indicate that the western 
border of the continent, from longitude 115° to the then shore of the Pacific, 
remained a land area, free from considerable lakes, from the time of its 
upheaval at the close of the Jurassic age. 

In the modern configuration of the country the most notable feature is 
the great mountain barrier of the Sierra Nevada and Cascade Range which 
defines the western limit of the fresh-water Miocene and Pliocene basins of 


452 SYSTEMATIC GEOLOGY. 


Oregon and Nevada. North of the latitude of the northern boundary 
of California the Sierra Nevada was not a barrier to the eastward exten- 
sion of the Cretaceous. The marine strata of this period, which abut un- 
conformably against the western face of the Sierra Nevada, in continuing 
northward continually pass farther and farther inland, until in eastern 
Oregon they abut against the western face of Blue Mountain Range. 
The shore during Cretaceous time, therefore, had a northwest trend along 
the Sierra Nevada, and then turned an angle with a slightly northeast 
trend, reaching the base of the Blue Mountains, which, like the Sierra 
Nevada, were uplifted at the close of the Jurassic age. 

So far as at present known, the highest of the marine series east of the 
present Cascade Range is the upper Cretaceous. It is not impossible that 
fiture search may develop the presence of overlying, conformable marine 
Kocenes. However that may be, prior to the Miocene age the line of up- 
heavals defining Cascade Range took place, isolating the basin of eastern 
Oregon from the sea. This chain of elevations, connecting southward with 
the Sierra Nevada, had also the effect of extending the depressed basin of 
eastern Oregon southward along the east base of the Sierra Nevada, 
through Nevada and into California, to an indefinite distance. 

The latest beds which were first upheaved to form Cascade Range, 
so far as now known, consist of marine Cretaceous. Unconformably, be- 
neath the Cretaceous, are sparingly seen the highly altered metamorphic 
rocks of the Sierra Nevada system, presumably of Triassic and Jurassic 
age, as upon the flanks of Cascade Range, where the east-and-west upheaval 
of Siskiyou Range joins it. Thus far in the exposures of the Oregon basin, 
east of the Cascades, so far as I know, marine Tertiaries have not been 
observed. In their absence, the natural inference is, that the Cascades 
were first outlined at the close of the Cretaceous. 

The only other reasonable hypothesis of the isolation of the eastern 
Oregon basin prior to the Miocene is, that the Cascades and the basin of 
Oregon were defined at the close of Eocene time, and that the marine 
Tertiaries seen upon the west side of the range will yet be found under the 
fresh-water Miocenes upon the east side of the range. There is nothing to 
render this probable; and the former hypothesis, that the marine Tertiaries 


RECAPITULATION OF TERTIARY LAKES. 453 


to the west are both Eocene and Miocene, and that Cascade Range was ele- 
vated at the close of Cretaceous time, is by far the more probable. On 
either hypothesis, the elevation was prior to Miocene time. 

The enormous thickness of the fresh-water Miocene beds in the basin of 
eastern Oregon is for the most part made up of the sands, tuffs, and rapilli of 
Miocene eruptions which found their vent beneath the lake itself, or along the 
crest of Cascade Range, and buried the sedimentary hills in deluges of lavas, 
ending in the erection of important volcanic cones. East of the Cascades, 
in the fresh-water basin, there are fully 4,000 feet made up for the most part 
of fine volcanic ejecta, while on the immediate west side the marine Ter- 
tiaries are chiefly detrital. Since the period of volcanic eruption covered 
the whole range of Miocene time, it would seem necessary that a consider- 
able portion of the marine Tertiaries lying west of Cascade Range should 
have been characterized by the presence of volcanic material. It is true 
that the prevalent wind is a west-to-east current in these latitudes, and that 
the fine volcanic dust and sand blown from innumerable vents along these 
Cascades would for the most part have drifted eastward and been accumu- 
lated in the inland lake. But enormous amounts of mud-flows and sands 
would necessarily have been carried away by the drainage westward. Far- 
ther south, in California, the marine Miocenes of the Coast Range are, as 
they should be, liberally intercalated with beds of volcanic origin. It is 
possible that the marine Tertiary along the western base of Cascade Range, 
when further explored, will prove to contain beds of volcanic origin ; 
but until it does, and in the absence of characteristic fossils, it would seem 
that these beds might be considered as Eocene. 

To put the geological alternatives briefly : Either, first, Cascade Range 
was first lifted at the close of the Cretaceous, in which case there is an 
unconformity between Cretaceous and Tertiary not observed in California 
nor in Siskyou Range; or, secondly, the uplift took place at the close of 
Eocene time, in which case we should expect to find marine Kocene con- 
formably over the Cretaceous in eastern Oregon. Until evidence shall 
accumulate to the contrary, it is most probable that marine strata were 
deposited over the greater part of Oregon until the close of the Cretaceous; 
that immediately thereafter Cascade Range was first upheaved ; and that 


454 SYSTEMATIC GEOLOGY. 


the basin of Eastern Oregon during the Eocene was a land area having free 
outward drainage. 

Whatever may have been the history of the region during the 
Kocene—whether eastern Oregon was dry-land area or a region of marine 
sedimentation—at the close of that age occurred a subsidence defining the 
long basin which, during Miocene time, was occupied by a lake from Wash- 
ington Territory far south into Nevada and California. 

From the Cascades and Sierra Nevada volcanic eruptions began with 
and continued through the entire Miocene age, pouring down upon the up- 
heaved sandstones on the western side as lava-flows, and delivering a vast 
amount of material into the newly outlined fresh-water basin east of the 
Cascades. The great volcanic rock formation of the summit and west side 
of the Cascades, and the great Miocene fresh-water formation on the east, 
are a result of the same series of eruptions. 

For the fresh-water Miocene lake which extended from the region of 
Columbia River, and perhaps still farther north, far south through Oregon 
and Nevada into California, I propose the name of Pan-Urr Lake, since 
that Indian tribe with its various sub-families covers so large a portion 
of its area. 

The beds of this lake, to which, in the Fortieth Parallel area, I have 
given the name of Truckee Miocene, are made up of, first, detrital rocks 
and gritty sandstones, with more or less conglomerate, never over 150 feet. 
Over this lie about 250 feet of palagonite tuff, which, for reasons already 
described, is referred to the age of the augite-andesites; over this, 250 
to 300 feet in Nevada, with a greater thickness in Oregon, of infusorial 
silica, followed by 120 feet of sandy, gritty rocks, purely detrital, but con- 
taining always a considerable amount of infusorial silica, succeeded by a 
fresh-water limestone of about 60 feet, in its turn succeeded upward by 
250 feet more of detrital grits, which give way to an enormous formation 
of volcanic tuffs of the trachytic period. The thickness of these trachyte 
muds in Nevada cannot be less than 2,000 or 3,000 feet ; in Oregon, accord- 
ing to the observation of Professor Marsh, they are even more fully devel- 
oped. It is in these volcanic muds that the enormously abundant Miocene 
fauna of this lake is mostly entombed. Out of the grits overlying the lime- 


RECAPITULATION OF TERTIARY LAKES. 455 


stone in Nevada have been obtained teeth of a rhinoceros, probably R. 
Pacificus. 

It was seen that at the close of Sioux Lake the White River Miocene 
beds, which represent a full equivalent, in time, of the Truckee series, were 
subjected to but slight mechanical disturbances. As described by E. 8. Dana 
and G. B. Grinnell, the only physical break in the conformable series, where 
in Montana the Miocene are succeeded by the great Niobrara Pliocene of the 
Plains, is a narrow zone of conglomerate. In the Fortieth Parallel exposures 
on the Plains, the Miocene and Pliocene are absolutely conformable, the line 
being simply arrived at by the characteristic skeletons of vertebrate animals. 

The condition of things at the close of the Miocene in the area of 
Pah-Ute Lake was entirely different. The beds of the Truckee Miocene 
series were thrown into bold folds, their dips reaching angles of 30°. The 
disturbances, therefore, which marked the close of the Miocene, were of a 
general gentle type in the Plains region, but show great intensity through- 
out the area of Pah-Ute Lake. The result of these disturbances was to 
enlarge enormously the lake areas in both provinces. I will first describe 
the outlining and development of the Pliocene lake and formations east of 
the Rocky Mountains. . 

Without any considerable local folding, the general basin of Sioux Lake 
was enlarged, it is probable, by gentle, wide-spread subsidence, until the 
new-formed lake overlapped Sioux Lake in every direction. Westward, 
it flowed to the very foot-hills of the Rocky Mountains; southward, from 
the margin of Sioux Lake in the region of northern Kansas, the lake 
extended itself through Indian Territory and Texas, and even into the 
present area of the Gulf; while northward it stretched over the whole sur- 
face of the Plains into British Columbia. 

For this new and enlarged lake of the Pliocene age I propose the 
name of CHEYENNE LAKE. 

The Miocene beds which formed the main bottom of this lake were gen- 
erally in an undisturbed condition, and the deposition of Pliocene which then 
began, has resulted in a sheet of fresh-water rocks, having a maximum thick- 
ness of about 2,000 feet against the foot-hills of the Rocky Mountains— 
in other words, close to the main influx of material—thinning out east- 


456 SYSTEMATIC GEOLOGY. 


ward to a shallow group along its eastern margin in Kansas, Nebraska, and 
Dakota. The materials of this series are coarsest next to the Rocky Moun- 
tains, and at a distance of about 200 miles east are of extraordinary fine- 
ness. They are composed of sandstones, conglomerates, and a few marly 
strata next to the Rocky Mountains, with unimportant chalky limestones, 
and over the middle area of the Plains, far removed from the source of sup- 
ply, are chiefly calcareous clays and sands of marvellously fine grain. 

For the general production of this lake within the United States there 
was required only a gentle, uniform subsidence of the bottom of the Mio- 
cene lake, and there is no reason whatever to suppose that a period of dry 
land intervened over the whole province of the Plains between the deposi- 
tion of the Miocene and Pliocene beds. Cheyenne Lake, in other words, 
was simply a wide, gentle extension of Sioux Lake. 

On the other side of the continent, in the region of Pah-Ute Lake, the 
conditions were totally different. Severe crumpling, as already mentioned, 
took place, and the mountainous country east from the eastern boundary 
of Pah-Ute Lake, which must have been on the meridian of 117°, became 
depressed, so that the lake, at the beginning of the Pliocene deposition, 
stretched from the base of the Sierra Nevada to the base of the Wahsatch, 
making a surface of eight degrees of longitude. The northward extension of 
this lake must have been far up the upper Columbia River, while its south- 
ward extent is at present unknown. 

For this lake, occupying the whole breadth of the present Great Basin, 
and parts of Idaho and Oregon, I propose the name of Suosnone Lake. 

Under the description of various Nevada localities, I have shown that 
the ejections of the trachytic period have furnished a large amount of the 
Truckee Miocene beds of Pah-Ute Lake. 

It was also shown, when describing under the Miocene section a local- 
ity at the west end of Montezuma Range, that at the period of the folding 
up of the Miocene beds the fissures then made gave vent to rhyolitic 
material. The rhyolites having, as is well known, always succeeded the 
trachytes in their period of eruption, it would seem that their ejection marked 
the beginning of the Pliocene. When we come to correlate the basalts, 
which were the last of the sequence of volcanic rocks, with the sedimentary 


RECAPITULATION OF TERTIARY LAKES. 457 


series, it is found that over the great Shoshone Lake a large part of the 
group, especially in Nevada and Utah, is subsequent to the basaltic out- 
flows. But in the middle of the present basin of Snake River, basalts are 
intercalated between distinctly Pliocene strata. It is therefore evident that 
the rhyolites were characteristic of disturbances which separated the Mio- 
cene from the Pliocene, continuing into the Pliocene, as is shown by Nio- 
brara fossils in stratified rhyolitic tuffs, and that the basalts are wholly within 
the Pliocene period, but, as regards the main massive eruptions, prior to 
the greater development of Pliocene strata. 

Within the field of the Fortieth Parallel Exploration, in the beds of 
the Humboldt Pliocene, which were the deposits of Shoshone Lake, organic 
remains are uncommon. A few fossils discovered in the rhyolitic tuffs of 
Bone Valley are of species identical with those of the Niobrara beds, the 
deposits of the Cheyenne Lake of the Plains. There is little doubt that, 
with the faunal differences to be expected from regions so widely separated 
as those of the Great Basin and the Great Plains, fossils of Shoshone and 
Cheyenne lakes will be found to be strictly coeval. The same is true of 
the Pah-Ute Miocene lake and the Sioux Miocene lake; and the recogni- 
tion of their absolute contemporaneity cannot long be delayed. For the 
purposes of our map, and in advance of any such detailed correlation, I 
have chosen to represent the four formations by different colors. It is my 
belief that the two Miocene and two Pliocene series are eastern and west- 
ern representatives of precisely the same intervals of time. 

Tertiary time in the region of the Fortieth Parallel is therefore repre- 
sented by nine lakes: four Eocene lakes which occupied the middle Cordil- 
leras in the region already described; two Miocene lakes, one in the prov- 
ince of the Plains, the other in eastern Oregon and western Nevada; and, 
lastly, the three Pliocene lakes, one of which was coextensive with a large 
part of the Great Basin and the drainage-system of the Columbia, and 
another covered the wide expanse of the geological province of the Plains 
from the Gulf far into British Columbia, and the third a much less important 
area in North Park and Platte Valley. 


The following is a statement of the proposed names, ages, and sequence 
of these Tertiary lakes: 


458 SYSTEMATIC GEOLOGY. 


TERTIARY LAKES. 


EOCENE. 
Middle Province. 
Ure Lake (Vermilion Creek Group, King ; Wahsatch Group, Hayden). 
GosIuTE LAKE (Green River Group, Hayden; Elko Group, King). 


Wasnakik Laker (Bridger Group). 
Uinta LAKE (Uinta Group, Emmons and Marsh). 


MIOCENE. 
Contemporaneous. 
fom ——— 
Province of Nevada and Oregon. Province of the Great Plains. 
Pan-UtE Lake (Truckee Group, King; John Sioux LakE (White River Group, Hayden). 
Day Group, Marsh). 
PLIOCENE. 
Contem poraneous. 
—————————E———— 
Province of the Great Basin. Middle Province. Province of the Great Plains. 
SnosHone Lake (Humboldt Nortu Park Lake (North Park CHEYENNE LAKE (Niobrara 
Group, King). Group, Hague and Hayden). Group, Marsh). 


The value of recognizing and naming these distinct lakes is evident 
from the historical point of view. Within one lake of the immense area of 
these sheets of water, surrounded as they often were by a widely varied 
topographical environment, the sedimentary accumulations might, and cer- 
tainly do, change from region to region. A geological explorer, finding a 
distinct group of rocks at one place within the area of a lake, is justified in 
giving it alocalname. Another investigator, ina remote region of the same 
lake, perhaps a thousand miles away, finds a group of rocks totally distinct, 
but belonging to the same horizon. He gives them a new local name. 
For the natural and satisfactory correlation of all these integral parts of the 
single series of sediments of one lake, it is positively necessary to have for 
each lake and its conformable deposits a distinctive appellation. In the 
interest of this precision I have sketched and named the leading Tertiary 
lakes touched by the Exploration of the Fortieth Parallel. So far as my 
own area is concerned, the boundaries of the lakes are approximately shown 
by the geological colors of the maps. My hope is, that fellow explorers of 
this interesting field will adopt the names I have given, and interpolate in 
the series such other lakes as do not enter my field, and that we shall soon 
be able to show in historic series the complete development of Tertiary 
lakes, 


(ii EXPE 


? O'S IRERS 


SiC LION Ye. 
QUATERNARY. 


GeNERAL Remarxks.—In eastern America, as set forth by Professor 
Dana, the Quaternary age consists of three divisions—the Glacial or Drift 
period, the Champlain or Depression period, and the Recent period ; the last 
being characterized in Europe by the reappearance of glaciers. It may 
otherwise be considered as a glacial period interrupted by an era of subsidence 
and of climate less favorable for the formation of ice, in which the northern 
ice-field and the local glaciers retired. In the Mississippi Basin, evidence of 
an interglacial era, as shown by Newberry,* is found in the presence of 
organic beds in the Drift. Lately, in his paper on the superficial geology 
of British Columbia, G. M. Dawsont has divided the Quaternary age of 
that region into, first, a greater Glacial period, in which, over a large part 
of British Columbia, moved from north to south a general ice-mass, which 
has left its traces in scorings and groovings, in the modifications of valleys, 
and a Bowlder-clay; secondly, a period equivalent to the Champlain, in 
which the country was depressed and the Drift rearranged; thirdly, a 
second Glacial period, in which, however, the great southward-moving 
ice-mass did not reappear, but which was characterized by glaciers radiant 
to the local mountain systems. The northwestern phenomena, as set forth 
by Dawson, when compared with those of Europe, show a marked coinci- 
dence in the chain of events of the Quaternary period. It is equally evident 
in Europe and British Columbia that the first glacial period was the greater ; 
that the second was limited, and its ice local. The Champlain was a period 
of depression and floods, and the Reindeer period a moderate second glacial 
period, not comparable with the first in magnitude or extent. 

In the field of the United States Cordilleras, we have so far failed to 
find any evidence whatever of a southward-moving continental ice-mass. 
As far north as the upper Columbia River, and southward to the Mexican 


*Report of Geological Survey of Ohio. Geology, Vol. I. 
t Quarterly Journal of the Geological Society, Vol. XXXIV, part 1. 
459 


460 SYSTEMATIC GEOLOGY. 


boundary, there is neither any Bowlder-clay nor scorings indicative of a gen- 
eral southward-moving ice-mass. On the contrary, the great areas of Quater- 
nary material are evidently sub-aerial, not sub-glacial. The rocks outside 
the limit of local mountain glaciers show no traces either of the rounding, 
scoring, or polishing which are so conspicuously preserved in the regions 
overridden by the northern glacier. Everything confirms the generaliza- 
tion of Whitney* as to the absence of general glaciation. 

Wherever in the Fortieth Parallel area a considerable mountain mass 
reached a high altitude, especially when placed where the Pacific moisture- 
laden wind could bathe its heights, there are ample evidences of former 
glacial action, but the type is that‘of the true mountain glacier, which can 
always be traced to its local source. In extreme instances, in the Sierra 
Nevada and Uinta ranges, glaciers reached 40 miles in length, and, in the 
case of the Sierra Nevada, descended to an altitude of 2,000 or 2,500 feet 
above sea-level Over the drier interior parts of the Cordilleras, the ancient 
glaciers usually extended down to between 7,000 and 8,(00 feet above the 
sea. In the case of the Cottonwood glacier of the Wahsatch, a decided 
exception, the ice came down to an altitude of 5,000 feet. 

The interior valleys of the Cordilleras, from California eastward to 
Wahsatch Range, are all filled to a varying depth with subaerial Quater- 
nary accumulations. Within the system of the Great Basin, from near the 
Mexican boundary northward to the region of the Columbia, the general 
configuration is that of parallel mountain ridges, alternating with trough-like 
valleys. In each one of these depressions is a considerable covering of 
angular and sub-rounded Quaternary gravel, always of an evidently local 
character, directly to be traced to the flanking mountain ranges. _ Its coarse- 
ness varies from large bowlders, weighing many tons, to fine gravel, sands, 
and clay. Except where it has been rearranged in the now extinct Qua- 
ternary lakes, it is altogether an unstratified deposit, brought down by the 
rush of floods from the flanks and canons of the mountains. It not infre- 
quently banks up against the foot-hills of the range from which it was derived, 
making a fringing deposit of from 1,000 to 2,000 feet in height, skirting the 


range for many miles with an inclined talus-slope. The most modern 


* Proceedings of the Academy of Natural Sciences of California, 1868, 


QUATERNARY. 461 


erosion has not infrequently cut the mountain cafions sharply down below 
the old talus-profile, wearing a narrow cut through the top of the Quater- 
nary slope, exposing sections of gravel from 50 to 200 feet in depth 

Wherever these talus-slopes are opened, they are found to be made of 
a confused pile of sands, gravels, and bowlders, in which angular chips are 
the predominating ingredient. Where, as is common over a large part of 
Utah and Nevada, the flanking hills are made up of limestone, the harder 
fragments of siliceous or granitoid rocks are closely cemented by a calca- 
reous tufa-like formation, which unites the whole into a sort of breccia. 

Not more than a thirtieth part of the entire surface of the Fortieth Par- 
allel area was ever covered by glacial ice. Analytical Map V. accom- 
panying this section shows the actually glaciated areas in blue spots. It is 
characteristic of the canons of these extinct glaciers that they give evidence 
of a gradual recession of the ice from its greatest extension until it entirely 
melted. This retiring from its greatest bulk was not a continuous retro- 
gression, but was marked by pauses at certain places long enough to permit 
the accumulation of considerable terminal moraines. In ascending one of 
the larger canons, as of the southern Uinta, there is observed a series of 
successive terminal moraines, and in passing to the upper heights of the 
ranges it is found that in the great snow amphitheatres, glacial markings, 
rock-polishing, and the arrangement of morainal matter are evidently fresher 
than in the lower levels or points of greatest extension. 

Since there was no northern Drift, if glaciers existed both in the first 
Glacial and in the second or Reindeer period, it is evident they must have 
occupied the same valleys; in other words, that the perpetual snows which 
hung about the crests of the névés after the disappearance of the main gla- 
ciers, during the Recent period encroached downward and pushed their ice- 
streams part way down the channel of the earlier glaciers. Furthermore, 
since the whole interior has been during the Quaternary period free from 
Drift and wholly isolated from the sea, proof of the two ice periods must be 
sought in other evidence than that displayed over the actual glacier-beds. 
As will be seen later in this section, the evidence of two periods of 
precipitation, with a drier interval, is found in an entirely distinct set of 
facts. 


462 SYSTEMATIC GEOLOGY. 


The present distribution of perpetual snow indicates islands of climate 
whose temperature and moisture combine to conserve permanent snow- 
banks. These present snow-fields, which in all cases are seen to linger 
about the amphitheatral sources of extinct glaciers, fail to prove that the 
relative glaciation, or rather the relative annual accumulations of snow, 
occurred in exactly the same quantitative distribution as at present. The 
traces of existing glaciers, their extent and thickness, and the low alti- 
tude to which they descend, are not found to be exactly proportional to the 
amount of snow now preserved. 

In March, 1871,* I announced the discovery of actual glaciers now 
existing on the mountains of the Pacific slope; meaning true glaciers, not 
moving masses of névé upon the steep slopes of the upper mountain flanks, 
but actual trunk bodies whose motion was not wholly the result of steep- 
ness of slope. The southernmost point at which living glaciers are now 
found is about latitude 41° 21’, at Mount Shasta, in the Sierra Nevada. 
Mounts Hood, Adams, St. Helens, Rainier, and Baker also bear true gla- 
ciers, which descend into the subjacent country to lower altitudes according 
as they are supplied from more or less extensive névés, or occupy mountain 
slopes successively farther to the north. 

Altitude alone, or northing alone, is not enough to produce a glacier 
descending far into the lowlands, since a steeper slope and a wider névé 
will converge more ice and force it farther down into the lowlands, upon 
a more southern peak, than a more gentle slope and a smaller amphi- 
theatral source farther to the north. 

The existing glaciers represent the relics of the former great system; 
and if the present climatic distribution were relatively the same as during 
the Glacial period, the few regions which now bear existing glaciers should 
represent the points of greatest glaciation during the ice period. If the com- 
parison of the existing glaciers with old ice-tracks proves that the greatest 
former glaciation did not coincide with the points where glaciers now 
exist, then in the former distribution of temperature and moisture other 
conditions must have interfered. Perhaps observations have not been car- 
ried far enough to make my conclusion final, but I am now of the opinion 


* American Journal of Science and Arts, third series, Vol. I. 


QUATERNARY. 463 


that present points of actual glaciation were not points of maximum glacia- 
tion during the ice age. 

For instance, valleys of the Uinta and Sierra Nevada show extinct ice 
streams thirty or forty miles in length and from 1,000 to 3,000 feet in 
depth, and although the peaks are among the most elevated in the West, 
there are no existing glaciers. On the other hand, the now glaciated flanks 
of Mount Shasta, while they show a former extension of glaciers greater 
than the existing ones, do not give evidence of a system comparable in 
magnitude with that of the southern Sierras. 

It is not proposed here to discuss the eause of the great climatic 
change which ushered in the Glacial period. Beyond the great change of 
level immediately preceding glaciation, and the sudden diminution of Plio- 
cene water-surface, there is nothing observed within the Fortieth Parallel 
area which throws the slightest light on this difficult question. Certain it 
is that no change in the relative expansion of land and water could have 
had any considerable effect in producing the extra precipitation necessary 
to bring about the glaciers. On the contrary, between the Pliocene and 
the Quaternary, all the actual features of the country seem to favor greater 
precipitation during the Pliocene, for the general climate was warm enough 
to tolerate palms, while at the same time the enormous water-surface must 
have given place to far greater evaporation than during the Quaternary. 
Although extremely restricted and absolutely local, the Cordilleran glaciers 
of our latitudes were undoubtedly the local expression of the general 
changes of climate which elsewhere produced the great ice-fields. 

The first and most interesting question which appeals to a student of 
this region is, why the northern ice-cap described by Dawson failed to over- 
ride the mountains of the middle Cordilleras and reach a latitude where the 
average annual condition of temperature is equivalent to that of the southern 
margin of the glaciated region of the eastern States. Why, in other words, 
were the eastern and western halves of the continent so dissimilarly 
glaciated ? 

Since Dawson’s observations of a general southward moving ice-field 
in British Columbia, there are no new facts showing the source of that 
glacial sheet, or establishing any connection between it and the Drift- 


464 SYSTEMATIC GEOLOGY. 


covered ground in the Mississippi Basin. Until both these questions are 
solved, generalizations as to the points of similarity and difference between 
the two sides of the continent during the Glacial age cannot be safely 
made. 

Regarded from the mere point of view of temperature, it is natural 
enough that the non-Drift-covered region should extend farther north on 
the western than on the eastern border of the continent, as do the isotherms. 
Opposed to this is the enormous amount of moisture which the eastward 
moving Pacific winds must have gathered from the evaporation of the warm 
floods of the Japan Current, and constantly poured over the elevated con- 
tinental border, but which in the period of glaciers did no more south of 
latitude 48° than to maintain the system of local ice-streams. If the 
eastern Mississippian and Atlantic border ice-sheet was, as I believe, of 
Greenlandic origin, it is difficult to explain why such vast accumulations 
of snow should have occurred, as compared with the west coast of Alaska, 
where the altitudes are great and the amount of moisture furnished by the 
Japan Current must have been far greater than the Gulf Stream could have 
thrown upon Greenland. The colder latitude of the latter place is the 
probable cause of the difference. 

Whatever the greater causes may have been, the Cordilleran surface 
south of Washington Territory was free from an ice-sheet, and the only 
ice-masses were small areas of local glaciers which did not cover two per 
cent. of the mountain country. 

Supposing the Arctic land configuration to be as now, and a new oscil- 
lation of climate to bring on the conditions of a glacial period, it is cer- 
tain that the present ice-masses would form the nuclei of new northern ice- 
fields, and Greenland would probably be the point from which the glaciers 
would move southward to cover eastern America, and the absolute dis- 
tance from such a centre would have something to do with the failure of 
the ice to override the Cordilleras. Dawson’s suggestion of a great centre 
of dispersion in Alaska, where an elevated and broad highland fronts the 
moisture-laden ocean wind, has, it seems to me, a high degree of probability 
in accounting for the southerly moving ice of British Columbia without 
recourse to that refuge of pure imagination, a polar cap. _ 


QUATERNARY. 465 


Supposing a low country like that of the average Mississippi Basin to 
extend westward to the Pacific during general glaciation, the southern 
boundary of the continental glacier would be determined by isothermal 
lines and direct distance from the source of supply. The heat-lines would 
curve northward very much as they do now, only in the absence of high 
mountains a given line would swing farther to the north on approaching 
the Pacific Ocean. The effect of the high portions of the Cordilleras is, of 
course, to bring a cooler climate farther south; in other words, to deflect 
the isotherm to the south of what its position would be in the absence of 
the extreme heights. The peculiar condition of the Cordilleras in the 
United States is such that, while the lower altitudes possess a comparatively 
warm climate, owing to the general thermal condition of the Pacific slope, 
the detached, elevated ridges and high, isolated peaks are islands of cold 
altitude-climate. Generally, then, it is a comparatively warm region, inter- 
spersed with islands of high-altitude cold. But for these elevations, there- 
fore, there would have been no glaciers whatever below the parallel of 48° 
over a great region whose equivalent latitudes in New England, Canada, 
and parts of the Mississippi Basin were covered with a general ice-sheet 
thousands of feet in thickness. 

Between the phenomena of the Champlain period in the East and West 
there are equally characteristic differences. Owing to the average profile of 
river grades in the East, the gravels, sands, and pebbles which were washed 
down from the surrounding country accumulated in the valleys, filling them 
full of deposits often hundreds of feet thick. There, too, at the close of the 
Champlain came a single great flood, and the phenomena of continental 
subsidence are distinctly observable. 

In the Fortieth Parallel area the general abruptness of mountain 
masses gave to the stream-beds such steep slopes that, instead of being areas 
of deposition, they were regions of terrific torrents, whose carrying power 
was sufficient to prevent accumulation, and whose freight of moving rock 
was enough to erode the great system of canons. There was no single 
final flood, such as Dana in his treatment of the New Haven Quaternary 
has demonstrated, and no moraine profonde left by the melting of a general 


ice-cover to furnish a ready-made source of detrital material. Lastly, 
30 K 


466 SYSTEMATIC GEOLOGY. 


excepting the slender evidence of Quaternary depression, adduced by 
Gilbert in his Lake Bonneville description,* the middle Cordilleras as yet 
afford no proof of Champlain subsidence. 

So, too, the Recent period has failed to record itself in the Fortieth 
Parallel region in a well defined system of river terraces, as in the East or 
in British Columbia. 

Since in the West the Champlain-period rivers cut cafons and threw 
their detritus into valley basins instead of filling river valleys, there are 
only in the cases of rare topographical exceptions those great fluviatile 
accumulations of gravels and sands in which the shrinking streams of the 
Recent period could record their recession in terraces. 

In the East the floods of the Champlain were due in great measure 
to the melting of the northern ice-field, not wholly or in prominent part to 
the rain or snow of local water-sheds. 

Over the Cordilleras, there being no ice-cap, the Champlain floods were 
derived from the local glaciers and the summer melting of mountain snows. 

In the East the glacial, Champlain, and Recent periods have ceased. 
Over the Cordilleras the work of all three periods is still progressing, albeit 
at a greatly reduced rate. 

In the latitude of this Exploration, owing to the absence of a great 
south-moving ice-field, the later local glaciers of the Reindeer period, if 
they existed at all, could not record themselves as the only system radiant 
to the local mountain groups, and thus distinguish themselves from the ice- 
streams of the earlier and greater Glacial period. Since in this region both 
must have occupied the same mountain valleys, we are yet without satis- 
factory grounds for separating the work of the two systems. 

It is therefore not practicable to treat the Quaternary age, as a whole, 
after the manner of writers on the phenomena of this interval of time in 
eastern America. 

The features of Fortieth Parallel Quaternary are — 

1. Glacial phenomena. 

2. Erosion and canon-cutting. 

3. The sheet of subaerial unstratified gravel and sand, which is a wide- 


*United States Geographical Surveys West of the One Hundredth Meridian, Vol. III. 


QUATERNARY. 467 


spread deposit covering all regions of interior drainage except the areas of 
Quaternary lakes. 

4. Quaternary lakes and their horizontal deposits now exposed by the 
desiccation of their areas. 

5. The chemical reactions, and deposits due to lacustrine desiccation 
and pseudomorphism. 

6. Modern and now forming débris of high mountains. 

7. Adolian erosion, still continuing. 

These are often so interdependent in time and in operation that it is 
best to treat them somewhat in combination, rather than categorically. 


Extinct Guaciers AND CaNons.—Upon Analytical Map V. accompany- 
ing this section are seen in blue, indicated in a general way, the areas for- 
merly occupied by glaciers. The high part of Colorado Range, which 
enters the map a little south of the parallel of 40° 30’, gives evidence of 
having been covered with glaciers for a breadth of about sixteen miles. 
From the forms of the peaks it is clear that large accumulations of névé 
snow covered all the spurs and ridges, while the valleys themselves are 
clearly modified by the abrading effect of the glaciers. As far north as the 
high group continues, namely, up to a point abreast of North Park, a dis- 
tance of about twenty-five miles from the southern limit of our map, the 
whole summit was clad with glaciers. 

Large trunk streams descended the canons of both branches of the 
Cache la Poudre as low as 6,500 feet in altitude. Down the Big Thompson 
from Hague’s Peak they descended to the same level, if not a little lower, 
and along a branch of the Big Thompson from Long’s Peak and in the 
region of Estes’ Park to about the same level. West of Long’s Peak, with 
an important tributary from Mount Richthofen, the upper glacier of Grand 
River reached to the foot-hills of Middle Park. 

The depressed region of Colorado Range included within the Laramie 
Hills was evidently at too low an altitude to act as a powerful condenser, 
and is absolutely free from glacial traces. That it had prominent snow- 
banks, and that much of the erosion is due to the influence of the cracking 
power of frost and the dislocation of blocks by the sudden expansion of the 


468 SYSTEMATIC GEOLOGY. 


waters filling the minute surface-fissures, is doubtless true, but there were 
no glaciers. 

So, too, the depression along Medicine Bow Range, north of Mount 
Clark, shows only the most superficial effect of snow-work. Medicine Bow 
Range is entirely devoid of true glaciation, except in the immediate vicinity 
of Medicine Bow Peak, where the single high crest formed a centre of 
moisture-condensation, giving rise to rather limited local glaciers, which 
descended each of the valleys to an altitude of probably 8,000 feet. 

From a little north of Clark’s Peak southward to the divide between 
North and Middle parks the foot-hills of North Park are covered with the 
terminal-moraine material of the system of glaciers which poured down the 
western slope of Colorado Range and actually pushed out upon the com- 
paratively level floor of the Park. 

Park Range, as indicated by the map, shows a glaciated region about 
sixty miles in length, with an average width of ten miles. On the eastern 
flank the ice descended to the level of North Park, and the whole foot-hills 
for a distance of fifteen or twenty miles are composed of accumulations of 
terminal moraine, which are built out in some instances two miles beyond the 
true rocky foot-hills, and 1,000 feet high. The average elevation to which 
the glaciers pushed down was about 8,000 feet. In the case of Park Range, 
there was neither a broad exposure of the elevated mass, nor the actual 
altitudes of Colorado Range in the same latitude. In consequence, the gla- 
ciers never descended to a lower altitude than 8,000 feet, or, at the lowest, 
7,600 feet; while from the superior dimensions and altitude of the névés of 
Colorado Range, the trunk glaciers were pushed down in particular cases 
to 6,500 feet, more than 1,000 feet lower than those of Park Range. 

The three bodies—the Colorado, Park, and Medicine Bow—present 
very similar phenomena of glacial erosion. The amphitheatres are all deeply 
sculptured in characteristic, round forms, the upland-valley bottoms are 
entirely occupied by smoothly abraded surfaces or roches moutonnées, and 
both main and lateral canons have the ship-like section characteristic of 
glaciated regions. Owing to the narrowness of the ranges, the lateral 
canons are exceedingly short, but they make up for their limited extension 
by an imposing depth. The Medicine Bow caiions are somewhat the shal- 


QUATERNARY. 469 


lowest, never exceeding 2,500 feet. Those in Colorado Range, in the 
region of Long’s Peak and Mount Hague, reach in extreme cases 3,500 feet. 

Considerable portions of the Archzan cores of these ranges have 
remained as islands above the limits of the sedimentation since pre-Cambrian 
time. The masses have therefore been subjected from that ancient date to 
degradation, either by surrounding oceans or by subaerial erosion, where 
lifted above the ocean limits. It becomes a question of great interest how 
much of the deep-caton sculpture which now exists was due to the erosion 
of the Glacial and Champlain periods, and how much to preéxisting effects. 
Whatever of the Archean islands were lifted above the general level of the 
Mesozoic sea must have risen to a considerably higher level than at pres- 
ent. If erosion had had the effect of producing canons prior to the Glacial 
period, it would seem as if these canons must have left some traces. That 
there were no great canons in the Archean hills prior to the deposition of 
the Paleozoic and Mesozoic, is shown by the contact-planes of the various 
members of the stratified series, which display smooth, broad slopes of the 
original Archean. The few irregularities of contact are due rather to 
gentle round projections of the Archzan than to such sharp reéntrant 
angles as would indicate camions. 

In the region of our portion of the Rocky Mountains, volcanic out- 
bursts are of such infrequent occurrence and limited extent that the evi- 
dence of continuity of canons down the Archzean slope and across the vol- 
canic masses is wanting. In the Sierra Nevada and Cascade Range, where 
many of the highest peaks are altogether formed of lavas, and where the 
older mass of the range has been frequently deluged with broad, volcanic 
sheets, evidence is abundantly conclusive that the period of canon erosion 
has been in great measure since the basaltic epoch, and that, as we have 
abundant proof, was within the limits of the Pliocene age. As Whitney 
has shown, deposits of Pliocene, themselves buried by basalts, have been 
cut through by the great canons of the Sierra Nevada, and left on the tops 
of the modern canon walls 3,000 feet above the present river-level. The 
pre-Pliocene drainage-lines seem never to have been other than broad, com- 
paratively shallow river-valleys, in nowise approaching deep, abrupt canon 
forms. 


470 SYSTEMATIC GEOLOGY. 


In passing westward from the Rocky Mountains, the next and by far 
the greatest accumulation of glaciers in our area is indicated as covering 
the whole lofty part of Uinta Range, from longitude 109° 30’ to 111° 15’, 
and extending north and south with an extreme limit of 50 miles. Upon 
the great plateau-like summit of the Uinta, which, at the time of the coming 
on of the Glacial period, cannot have been less than 15,000 to 17,000 feet 
high, immense masses of snow accumulated, which have produced upon the 
nearly horizontal summit-region of the range very peculiar topographical 
effects. On the north side the glaciers descended to an extreme level of a 
little above 8,000 feet. Bear River and Smith’s and Black’s forks show 
well defined glaciation and moraine material down to between 8,000 and 
J,000 feet. Since the actual topographical summit of Uinta Range was 
along the northern edge of the broad, plateau-like upland, a greater glacier- 
shed was exposed to the south. In consequence, the glaciers on that side 
descended on Ute, Lake, and Du Chesne forks to elevations varying from 
6,500 to 7,200 feet. As is roughly indicated by the blue color upon the 
accompanying map, several of the trunk glaciers projected beyond the gen- 
eral névé region, both on the north and south sides of the range, from ten 
to twenty miles. 

The Uinta field was therefore comparable with the present Alpine 
system, but decidedly grander in its accumulation of snow and ice. Over 
the greater part of the upland the quartzite and sandstone series, which 
form the summit of the Uinta, are inclined at no greater angles than 5° to 
6°. In this comparatively horizontal position the glacial erosion has cut 
almost vertically down through the beds, carving immense amphitheatres, 
with basin bottoms, containing numerous alpine lakes. The whole ap- 
pearance of these broad, smooth-curved canons is as if a glacier had melted 
out very recently. The minutest striations and polishings are well pre- 
served. The final débris which was dropped when the glacier melted, rests 
where it fell on the bare and polished rock surfaces; accumulations of 
lateral moraine are observed in points of topographical shelter; and but 
for the forest and late accumulations of meadow-land, the whole region 
would wear the aspect of having been just dispossessed of its glaciers. 

Here, as in the canons of the Rocky Mountains, the post-Glacial ero- 


QUATERNARY. A471 


sion has done an absolutely trivial work. Modern streams which occupy 
the beds of these old glaciers have worn insignificant shallow troughs in 
the smooth valley-bottoms; but, owing to the average gentleness of the 
inclination of these canons, these extremely rare cuts never exceed 10 or 20 
feet, and amount to nothing as topographical features. Compared with the 
work of the real canon-cutting age, the erosive force of existing streams 
is as nothing. 

Along the lower course of the canons terminal-moraine material is 
observed, but never in such remarkably thick, conspicuous accumulation 
as in the parks of Colorado. On the contrary, lateral moraines are far more 
developed here than in our section of the Rocky Mountains. On the south 
side of the Uinta are trains of moraines extending many miles in length, and 
flanking valleys whose bottoms are from 2,000 to 3,000 feet below the top 
of the moraine. In the horizontal Uinta strata the walls of the upper am- 
phitheatres occupied by the former névés are steeper than the corresponding 
walls of granitic regions. The ridges separating amphitheatres are much 
thinner, and erosion, while it seems to be no deeper, acted more ver- 
tically. The narrow intermediate ridges which separate the present amphi- 
theatres show upon their walls the distinct horizontal bedding of the sand- 
stone and quartzite. 

While post-Glacial stream erosion has done little or nothing in this 
country in the way of cutting canons, the frost and ice work of the summit 
has been immense. The whole peak region is seen to be riven with innu- 
merable cracks, which are evidently not the result of fault or of fissure at the 
time of upheaval, but belong to that class of shallow, interlacing cracks 
which are due to unequal superficial expansion and contraction in a region 
alternately chilled by radiation and warmed by the sun. 

Upon the steep slopes and sharp, blade-like ridges, the results of such 
fissuring, together with the leverage of expanding ice, have the effect to dis- 
lodge large fragments of rock and produce immense slopes of débris. The 
shapes of this débris are altogether angular, showing in no case any of the 
effects of attrition seen upon the bowlders which have been embedded in 
the bottom of a moving glacier, even for a short distance, or such as have 


been grated together in the motion of lateral moraines. That this débris is 
5 Do 


472 SYSTEMATIC GEOLOGY. 


altogether since the last Glacial period, is evident from its angular and un- 
striated character and from the essential difference which it displays from 
the true Glacial débris to be seen everywhere in the middle of amphithe- 
atres resting upon the roches moutonnées. 

This shattering action is evidently quite analogous to that which takes 
place in exposed rock at high altitudes in countries now glaciated, and which 
is the source of all morainal materials. The arréts of the Alps, and in gen- 
eral all the exposed portions of rocks in glaciated countries, are subjected 
in like manner to the disintegrating forces of extremes of temperature and 
ice. That this action is now progressing, is proved by the constant dislo- 
cation of blocks through the high mountain regions of the Cordilleras at all 
hours of the day, but especially when a sudden chill (as during the hour 
after sunset) has the effect of congealing the percolating waters. 

Upon the summits of the Rocky Mountains, the Umta, and Wahsatch, 
and at very many points of the ranges near the Pacific coast, I have heard 
during the day thousands of blocks dislodge themselves and bound down 
the slopes. It is evident that such accumulations of débris during the occu- 
pancy of the glaciers would either work down and be embedded in the under 
surface, or, if escaping fissures, would be disposed along the sides and sur- 
faces in the form of transported rocks and lateral moraines. Hence these 
enormous accumulations must be considered altogether post-Glacial; and 
throughout the Cordilleras, in all the high mountain ranges, they form a 
very conspicuous feature. In many instances they must amount to fully 
1,000 feet in thickness. In the Sierra Nevada, where all these phenomena 
are on a grander scale, I have seen débris-slopes measuring 4,000 feet from 
top to bottom. 

The transportation of material by the modern rivers of the Uinta is 
comparatively slight. Decay of rock material is also extremely slow, 
and its products, gathered in the various alpine meadows, represent a com- 
paratively insignificant total. But the gradually increasing débris-slopes are 
telling seriously on the mountain forms. Already many of the dividing 
ridges in the Uinta upland are nothing more than blades of rock, with débris- 
trains on both flanks covering the whole mass of the solid rock. It is easy 
to see that this disintegration and tumbling down of detritus will continue 


QUATERNARY. 473 


until the solid ridges are shattered and made over into débris-piles, and the 
whole summit will be nothing more than ridge-like piles of débris separated 
by broad basins, in whose unencumbered medial portions the old glaciated 
surfaces of rock will be shown. Of course the rapidity of this action would 
altogether depend upon the texture and structure of the rock upon which 
these forces are exerted. The loose, quartzitic sandstones of which the 
Uinta highlands are formed, offer exceptionally easy conditions; but in the 
more solid and less jointed bodies of Sierra Nevada granite the action is 
quite as intense, owing probably to the greater extremes of temperature to 
which that region is exposed. 

Accumulations of terminal moraines in the Rocky Mountains, although 
found at successively higher positions upon the bed of the old glacier, thus 
indicating a gradual recession of the ice-mass toward the summit region, do 
not display the same well marked paraboloidal forms and sharp crests which 
are shown in the successive cross-ridges of the glacier-beds of the Sierra 
Nevada. 

In passing down ice-fed streams, the fine material which is the result 
of abrasion by the bottom of a glacier must have distributed itself either in 
Quaternary lakes or else passed onward to the sea. 

In every great glacier-bottom of the Uinta there are the characteristic 
glacier lakes and meadows, hollows scooped by the extinct glacier, which, 
upon the final melting of the ice, were rock basins filled to the brim with 
the waters of the melting perpetual snow, and which have subsequently 
been more or less silted up with the fine sand of the region, filling the lake 
and resulting in those open bits of verdant meadow which are such a 
characteristic and beautiful feature of Cordilleran glacier-valleys. The 
process of silting up these lakes is slowly going on; and here on a minute 
scale is seen the whole principle of delta formations, silt and vegetation 
combining to build out as complicated and characteristic deltas as those of 
the Mississippi or the Nile. 

A glance at the glacier designation upon Wahsatch Range in the 
accompanying map will show three spots of color indicating the former 
existence of ice. The high group at the head of Cottonwood and Ameri- 


can canons had an extension of twenty miles from north to south, by at 


474. SYSTEMATIC GEOLOGY. 


least ten in the direction of the cafons. Mill Canon, Cottonwood, Little 
Cottonwood, and American Fork had their glaciers, which have left ordi- 
nary U-shaped valleys and characteristic traces of ice-abrasion and 
accumulation of morainal material. 

The valley of the Jordan at the western base of the Wahsatch is but 
a few feet above the level of Salt Lake. In consequence, the narrow Wah- 
satch Range, which rises to an elevation of about 12,000 feet, has upon its 
westward slope a steeper and deeper declivity than is seen elsewhere in 
the Fortieth Parallel area, and hence down these steep slopes the glaciers, 
though limited, pushed to a lower level than upon the Uinta or Rocky 
Mountain slopes. The glacier of Little Cottonwood came down to an 
elevation of 5,000 feet, or nearly to the mouth of the canon, and its 
terminal-morainal material covers nearly the whole gate of the gorge. 

On the eastward slope, toward Provo Canon, ice was confined to the 
higher summit regions, and down the eastern side in general there were 
but slight local glaciers. Along the upper tributary canons which feed 
Cottonwood and Little Cottonwood canons, the glaciated surfaces are dis- 
tinctly shown wherever the rock has a position and character fitted to 
retain them. 

Here again the slopes of débris, though not on so large a scale as in 
the Uinta Mountains, are a prominent feature of the topography, and are 
rapidly progressing toward the obliteration of the solid parts of the moun- 
tains. In the case of granite bodies here, this disintegration is less rapid 
than in the quartzites and other distinctly bedded formations. Even in 
the hardest granites, however, it is rapidly progressing, and, as in the Uinta, 
the final obliteration of the solid ridges is only a question of brief geologi- 
cal time. From this should always be excepted those vertical precipices 
due to faults and fissures, whose contour protects them from disintegration. 

Farther north in the Wahsatch we have observed two minor locali- 
ties, one east of Farmington and the other on Ogden Peak, in both of 
which glaciers were present; and although they piled up a considerable 
amount of morainal d¢ébris on the eastern slope of the range, they 
nowhere descended below 7,000 feet, and perhaps not below 7,500. The 


actually lowest point of descent is difficult to determine, owing to the dis- 


QUATERNARY. 475 


integrated Tertiaries and the more recent accumulation of modern material 
over the moraines. They are, however, of no special scientific interest. 
The glaciers of Humboldt Range were confined to two regions, one 
the high group lying west and northwest of Franklin Lake, and the 
other the detached elevated mass north of Sacred Pass, in the region of 
Clover Peak and Mount Bonpland. At both of these points the summit of 
the range gives ample evidence of glaciation. The upland amphitheatres, 
owing to the narrowness of the ridge, never have the broad, flat bottoms 
characteristic of wider ranges. On the contrary, each glacier sloped rap- 
idly from the head of its névé, and developed at once the deep, ship-like 
section. The glacier of the South Fork of the Humboldt, which descended 
along the western side of the range, carved canons over 3,000 feet in 
depth. Standing at the top of the South Fork xévé-slope above Lake 
Marian, and looking down the eurved course of the ancient glacier, the 
canon flanks and bottom are seen to be everywhere smoothed down to a 
general graded slope, to be more or less encumbered by the general débris 
which was deposited when the ice finally melted, and to show here and 
there more or less roches moutonnées. In general, the roches moutonnées over 
the whole of the Fortieth Parallel exposures are less frequent than broad, 
flat, smooth-polished surfaces. The glacier of the South Fork, which de- 
scended perhaps lower than any other in the range, being much the 
greatest, reached an altitude of 6,500 feet. Along the eastern side of the 
range, particularly in the Mount Bonpland region, the sharp eastern slope 
is deeply carved by rounded amphitheatres having nearly perpendicular 
walls. In this northern group of glaciers the rocks upon which they acted 
were of gently westward dipping beds of gneiss and quartzite. As a con- 
sequence, the nearly horizontal eastern edges were exposed along the 
eastern slope of the range, and the canons carved down these edges in 
sharp, almost precipitous faces, while in descending on the west they fol- 
lowed the backs of the strata and carved less deeply. The gorges on the 
west, coming down from Mount Bonpland and Clover Peak, rarely show a 
depth of over 1,000 feet. The eastern foot-hills are encumbered with 
glacial débris, both under Mount Bonpland and in the region of the Over- 


land Ranch. 


476 SYSTEMATIC GEOLOGY. 


Standing upon any one of the high summits of the glaciated regions, 
it is interesting to look down upon deeply carved glacial valleys which 
open out upon the plains on either side, having in their bottoms innumerable 
glacial lakelets which reflect the dark blue of the sky and contrast strangely 
with the gray glacial wreck and morainal material and the dusky alpine 
vegetation. In the northern, or Mount Bonpland group, the rocks, having 
a more compact, solid texture, are more easily converted into débris piles, 
while in the southern region, owing to the readier decay of the granitoid 
mass, there is more fine gravel and less sharp, angular débris. Upon a 
rock which easily crumbles it is evident that the cracking force of sudden 
contraction would have a minimum effect; and there is no glaciated region 
within the Fortieth Parallel limits where débris plays so limited a réle as in 
the region of White Cloud Peak and Lake Marian. Even here, however, 
there are some slight débris slopes, which are of course referred to post- 
Glacial disintegration. 

West of Humboldt Range the points of actual glaciers are but three, 
and they amount to absolutely nothing as geological phenomena. 

At Shoshone Peak, at Quiednanove or Star Peak in the West Hum- 
boldt, and on the high summits of Granite Springs Range north of Mud 
Lake Desert, are isolated points sufficiently high to act as slight con- 
densers, and to have developed insignificant local glaciers. In no case did 
the ice of these points descend below 7,500 feet. 

The lowest points, therefore, to which a glacier of the Fortieth Parallel 
descended were in Little Cottonwood Canon, 5,000 feet above sea-level, 
and on Ute Fork on the south side of the Uinta Mountains, where the ice 
reached 6,600 feet. Upon the grander slopes of the Sierra Nevada, in lati- 
tudes somewhat to the south of the Fortieth Parallel, glaciers forty miles in 
extent poured down the great canons of the Sierras to an altitude of cer- 
tainly not more than 2,400 feet, and possibly to still lower levels. The 
superior size and importance of the Sierra glaciers are due not alone to the 
greater altitude of the névé, or to a wider extent of tributary surface, but 
also to a climatic difference, which may be observed even now between 
the Sierras and the interior ranges. 

While the blue color on the accompanying map shows the distribution 


QUATERNARY. ATT 


and extension of actual glaciers, it presents absolutely no indication of 
the snow-distribution of the same period. With the exception of the 
three detached localities in western Nevada, the glacier localities exactly 
represent the present regions of perpetual snow; that is to say, at the head 
of each one of the cations of extinct glaciers are banks which are frag- 
mentary relics of the old névé, varied annually in their depth and extension. 
Owing to the frequent slight oscillations of climate, these snow-fields either 
advance or shrink from year to year, the residual autumnal bank showing 
very great variation. 

On highly inclined slopes, where the snow accumulates to a consider- 
able thickness and solidity by pressure and regelation, it compacts itself 
into a quasi-icy mass, and on sufficiently inclined slopes develops a down- 
ward motion. Motion alone, however, does not constitute a glacier, since, 
as is well known, all the névés of true glaciers possess a motion. 

Mr. Muir, in his studies of the high Sierra Nevada, has been fre- 
quently announcing the discovery of glaciers, based on simple evidence of 
motion. Years before he entered the Sierra Nevada, his identical snow-fields 
were studied by several members of the Geological Survey of California, and 
their motion was as well known to them as to him. It is a nice matter to 
draw the line between a well compacted moving névé and an actual glacier; 
but the distinction is a true one.* 

All the snow-banks of the Fortieth Parallel, when on slopes of over 
20°, possess the characteristic interior motion of glacier ice. But they are 
nothing more or less than the remnants of névés, and in extraordinary seasons 
all of them are obliterated. In the dry season of 186465 the writer 
examined many of the regions since described by Mr. Muir in the Sierra 
Nevada, and in not a few cases his so-called glaciers had entirely melted 


* Agassiz, in his Ltude sur Les Glaciers, page 43, says, ‘“ La limite supertficielle entre le glaccier et le 
névé est 1A ot la glace de la surface passe de l’etat compacte ou sub-compacte a letat grenu.” And again, 
on page 44, “ Le passage du glacier au névé n’est moins que tranché a la surface ; il dépend en beaucoup 
de cas de la position du glacier, de la vitesse de sa marche, et @une foule d@autre circonstances. M. 
Desor a cu Vheureuse idée de chercher un moyen plus str d’en apprécier la limite, et il a jrouvé que 
celle-ci ne commencent 4 surgir que 1A ow Ja glace a acquis une certaine consistance; car, comme nous 
le verrons plus tard en traitent des moraines, il n’y a que la glace compacte qui soit susceptible de pousser 
les blocs a la surface; les névés n’en sont pas capables, & cause de leur incohérente. L’apparition des 
moraines 2 Ja surface du glaciers indiquerait ainsi Ja limite certaine entre les glaciers proprement dits et 
les névés.” 


478 SYSTEMATIC GEOLOGY. 


away. The absurdity of applying the word “glacier” to a snow-mass 
which appears and reappears from year to year will be sufficiently evi- 
dent.* All winter snow-fields move when on a sufficiently inclined slope. 
I have seen the winter snows, averaging six or eight feet deep at the 
Emma Mine, in the Wahsatch, move down the mountain flank with such 
power as to overturn and crush strongly constructed buildings; yet these 
same fields promptly disappeared on the approach of summer, and gave 
way to abundant herbaceous vegetation. Motion alone is no proof of a 
true glacier. 

Since so small a fraction of the Cordilleras was covered by ice during 
the Glacial period, it becomes an interesting question to determine what 
were the conditions and geological operations during the Glacial period in 
those parts of the country which were not subjected to actual glaciation. 
While the U-curved canons are absolutely confined to the demonstrated 
tracks of glaciers, other canons shaped like a V, due unquestionably to 
aqueous erosion, are traced down the less elevated parts of the same 
ranges on which glaciers occur, and also on all ranges of any considerable 
elevation in the Cordilleras. As to the Y canons, it is evident that they 
were either excavated by the glaciers themselves or else were preéxisting 
gorges modified and given their present cross-section by the rocky under- 
surface of the glacier. That they were not Tertiary, is evident from the 
fact of their being cut in many places through the basaltic flows which 
were clearly of late Pliocene. It is evident that the canons post-date the 
most recent volcanic outpourings of the Fortieth Parallel. Recent volcanic 
activity, producing lava streams later than the canons, and even flowing 
down the cajions, is described to the south of our work by J. W. Powell; 
but such phenomena do not occur in the field of this work. 

Canions, as before remarked, occur upon all the ranges, as well in non- 
glaciated as in glaciated regions, the only difference in their phenomena 
being the rounded cross-section of the glacial carions, and the broad, amphi- 
theatral forms at their heads, and the V shape of water-worn gorges. In 


*It isto be hoped that Mr. Muir’s vagaries will not deceive geologists who are personally unac- 
quainted with California, and that the ambitious amateur himself may divert his evident enthusiastic 


love of nature into a channel, if there is one, in which his attainments would save him from hopeless 
floundering. 


QUATERNARY. 479 


instances of long glacial cations which descend to levels considerably below 
the terminations of the ice-limit, the cross-section of the canon changes 
rapidly from a U to a V shape. The continuity of single cations changing 
from the U to the V section shows, either the synchronism of the two forms 
of sculpture, or that the round-bottomed upper parts of canons are later 
modifications of the V gorges. All the sharp cafions in the non-glaciated 
parts of the ranges, and in ranges which were always wholly destitute of 
glaciers, are the result of the eroding power of torrents derived from the 
immense precipitation of the Glacial period. 

In the sculpture of the summits and peaks of the non-glaciated ranges 
is also clearly to be seen the action of névé erosion, in the easily recogniz- 
able ice-work which results in amphitheatres. An examination of all 
the peaks of our region shows a majority having a sharp side to the north 
and east. This, of course, is true only where erosion has been the dominant 
force in producing the shape of the peak. In the case of faulting and 
unusual local toughness of strata, as also in those rocks which easily dis- 
integrate instead of splitting asunder from the effects of cold, there is no 
recognizable preponderance of steep faces to the north and east. 

The greater part of the ranges within the Fortieth Parallel area are 
traced approximately from north to south, and it is easy to see that upon the 
shaded or north side of the peaks, ice would remain longest and continue 
longest to do its shattering work. But the equal number of steep faces to 
the east is to be accounted for by another set of causes. The dominant wind 
over the whole Cordilleras is the return trade, which blows from a little 
south of west and unloads its moisture during the seasons of precipitation on 
the higher parts of the ranges. Owing to the velocity of this wind, a greater 
amount of snow falls in the eddy on the eastern or lee side of the ranges 
than on the windward side, and in consequence the snow-banks on the east- 
ern summits are thicker and linger longer into the summer than those on the 
western. That the north and east sides of mountains have been most snow- 
burdened, and hence most glaciated, is very clearly shown on such peaks 
as Mount Shasta in California, a single, immense, isolated volcanic cone, 
presenting upon all sides approximately the same surfaces for snow to rest 
upon. The glacier valleys which are eroded down its sides and extend out 


480 SYSTEMATIC GEOLOGY. 


through its foot-hills are a remarkably clear record of the distribution of 
ice-work. The southwest half of the mountain, as compared with the north- 
east, had the smaller glaciers, and retains to-day infinitely the lesser amount 
of snow. Only broad banks of moving xévé exist upon the former side, 
while upon the north and east active glaciers are still doing their work, and 
the ancient moraines are on a scale greatly superior to those of the other 
half. So, too, the northern and eastern exposures of Mount Shasta are most 
deeply sculptured away by glaciers, and they consequently have a much 
higher surface-angle than the other flanks. 

This rule, which is true of Shasta, is true of all the other high volcanic 
peaks of the North American Cordilleras, and when applied to the configu- 
ration of mountain ridges is found to be applicable in their minuter topog- 
raphy. A great majority of the granite peaks of the Sierra Nevada, as well 
as the high lava peaks, and in great part the individual mountain peaks 
upon the ridges of the Great Basin region, show the influence of this wind- 
governed distribution of snow, in the steepness of their eastern slopes, and 
in the lingering ice-action under the northern shade of the rock-masses. 

The dip of the beds and the different hardness of mountain materials 
have, of course, often had a leading effect in giving the configuration; but 
so far as it is determined by forces of erosion, that erosion has been greater 
upon the north and east sides. Had erosion been due in any considerable 
extent to rains, it is clear that the accidents of original form would have 
dominated and determined the lines of drainage and the forms of peaks. 
Had water-erosion formed the peaks, they would have been cut by deep 
ravines, which usually is not the case. On the contrary, they are carved 
away in broad, recurved amphitheatral shapes, such as could never have 
been the result of water. And the effect of streams is evidently limited to 
that portion of the drainage beyond the limits of the névé action. 

There are, then, over the whole Cordilleras three types of erosion which 
have created the chief topographical forms—névé, glacier, and torrent work. 

First, and highest in point of altitude, is the évé erosion which has 
resulted in glacier sources, amphitheatral forms, broad recurved mountain 
faces, and in post-Glacial time in the débris-piles of all the regions of the 


high summit. This energetic degradation is now tearing down the solid 


QUATERNARY. 481 


ridges which formed the peaks and bounded the amphitheatres during the 
Glacial period. Névé action is varied greatly in intensity, having a maxi- 
mum on the high summits of the Sierra Nevada, which by their altitude and 
proximity to the moisture-laden wind of the Pacific receive by far the greatest 
relative snow-fall. There, especially in the region between the head of 
Stanislaus River and Walker’s Pass, which was the great glacier region of 
the range, the summit peaks and middle Sierra slopes are now encumbered 
by enormous slopes of débris, nearly all of which have accumulated since 
the occupation of the amphitheatres and canons by glaciers. 

On Mount Shasta the relics of former great glaciers are in some instances 
entirely buried by débris, and the very existence of some of them would 
have been unknown but for the accident of a very warm summer, when 
the writer was enabled to detect the presence of long bodies of moving ice 
beneath deep accumulations of angular and sub-rounded débris. In other 
words, it is evident that the production of intense névé erosion does not 
require any very deep accumulation of snow, and that a comparatively 
slight annual snow-fall in the higher altitudes will produce an immense 
shattering force, while a very large accumulation of snow would produce 
a glacier and to some extent prevent the shattering effects of mévé erosion. 

The size of the blocks developed by the névé shattering differs widely, 
according to the material and its own interior structure. Brittle bedded 
quartzite offers the easiest materials for contraction and expension to work 
upon ; and in consequence its angular blocks are not only easily developed, 
but the removal of the blocks, which takes place by the leverage of ex- 
panding ice frozen in the cracks, is facilitated by sliding the shattered rock 
along the smooth bedding-planes. Consequently, in all regions where high 
peaks are formed of quartzite, we find a very great accumulation of débris, 
which varies in size according to the hardness, uniformity of texture, and 
thickness of bedding of the formation. Conspicuous examples of this are 
the whole summit of the Uinta, the quartzite strata flexed around the 
granite of Mount Clayton in the Wahsatch, Pilot Peak in Ombe Range, 
and Dome Mountain in the Toyabe. This same action is also observable 
in some of the limestone heights, especially in those of Ogden and Weber 


canons, where slopes of over 3,000 feet are actually covered with rough, 
31 K 


482 SYSTEMATIC GEOLOGY. 


angular fragments that have been dislodged from the tops and dashed down 
the slopes. Among the granite débris of the Sierra Nevada are the largest 
specimens of detached fragments that I have seen. On some of the slopes 
composed of uniform and very compact granite, blocks of twenty or thirty 
feet in diameter are not unknown. 

As a whole, this process of disintegration has been in operation from 
the beginning of the Glacial period in all high Cordilleran regions, and as 
soon as the glaciers disappeared it began upon the exposed sides of their 
canons, continuing its work up to the present day. 

In the immediate future, in a geological sense, unless some climatic 
change takes place, every lofty peak and ridge of the Cordilleras, except 
those which from their precipitous faces or from other peculiar causes are 
defended from the action of snow, will be covered with a protecting mass 
of disintegrated and shattered blocks. Nota few instances may be observed 
where this has actually taken place, and the peaks and surrounding ridges 
are mere mounds of débris, which in their turn are rapidly shattering into 
angular gravel and forming gravel-clad peaks and ridges. This ice-sculp- 
ture is of course reduced to a minimum in a period of maximum glaciation. 
It is evident that the Himalayas are ina condition similar to the Cordilleras 
in relation to this process. The glaciers have shrunken immensely from 
their earlier Quaternary extension, the d¢bris-slopes are vastly greater than 
any elsewhere exposed in the world; and the phenomenon of actual glaciers 
pushing along under an enormous load of superincumbent débris which I 
have mentioned at Mount Shasta is seen in the Himalayas on an infinitely 
greater scale, as for instance the glaciers of the upper Ganges. Except such 
peaks as are the result of upheaval or ejection, all the high mountain sum- 
mits are the result of ice sculpture, none of the modern details having been 
given since the disappearance of the Glacial age. In the total amount of 
disintegration and transportion of rock now progressing, the labor of névés 
must be considered the most important element. 

The glacial canons, as already mentioned, reach a maximum depth of a 
little over 3,000 feet; and it becomes a question of great interest to determine 
whether this immense amount of excavation was actually the result of the 
abrading force of moving glaciers with their moraines profondes, or whether 


QUATERNARY. 483 


the canons are the result of aqueous erosion afterward modified by glaciers. 
There is not a particle of direct evidence, so far as I can see, to warrant the 
belief that these U-shaped canons were given their peculiar form by other 
means than the actual ploughing erosion of glaciers; nor do the objections 
to this belief advanced by certain observers, based upon the moderate amount 
of detritus transported by the existing glacier-streams of the Alps, seem to 
be worthy of serious consideration, since the Alpine glaciers of the present 
day are at best but the shrunken relics of the former system; and with the 
vastly greater accumulations of snow in the ice period there is every reason 
to believe that the thickness, movement, and energy of the glacier must have 
been much greater, and that its power of abrasion would be correspondingly 
increased. 

The transported material of the Glacial period was of two kinds: first, 
fragmentary, angular blocks, which were disintegrated from the summits by 
névé action; and, secondly, the fine silt which is carried out by sub-glacial 
waters and borne down in the glacial rivers. The entire drainage of the 
Fortieth Parallel region west of the Wahsatch poured into a series of lakes 
which occupied the present basins of Utah and Nevada and many of the 
valleys of the upland Nevada plateau. The silt was spread out upon lake- 
bottoms of the period, and forms the lacustrine deposit which is designated 
upon the geological maps of the Atlas as Lower Quaternary. In several 
limited and exceptional cases this is still covered by relics of ancient lakes; 
in general it has been laid bare by subsequent desiccation of the early 
lakes, and covers the bottoms of their basins with a horizontal sheet. 
Excepting a few wells and shallow cuts of very modern erosion, it cannot 
be examined, since the drainage of the present period, instead of opening 
up sections, has constantly the tendency to bury it beneath the detritus 
now accumulating. 

East of the Wahsatch the entire country possessed, during the Quater- 
nary period, a free drainage to the ocean, from the basin of Green River 
down the Colorado, and from the country east of Rawlings Station into the 
Mississippi, through the various branches of the Platte. There are here, 
consequently, no lacustrine Quaternary deposits worthy of note, and the 
entire Quaternary age is represented by accumulations along the valleys 


484 SYSTEMATIC GEOLOGY. 


of the rivers, and a thin variable coating of unstratified zolian Quaternary, 
which is nearly everywhere found over the surface, except where washed 
off by recent erosive forces or denuded by winds. The Quaternary valley 
deposits following the rivers and their tributary streams east of the Wah- 
satch are of considerable thickness, but possess, with a few local exceptions, 
no regular system of terraces such as marks the Recent period in eastern 
America. While the valleys give evidence of the existence of former great 
rivers, there are no successive periods of recession, and in general nothing 
like the important deposit of Champlain gravel displayed by the rivers of 
the East. It is quite possible, however, that if there were terraces formerly 
developed along the river courses, they have been subsequently obliterated 
by great floods. As it is, the rivers usually flow over a Tertiary or Creta- 
ceous plain, and display on their banks the rocks of those periods, the 
broad flood-plain of the river being usually flanked by a single but variable 
low bluff of Quaternary sand and gravel a few feet in height. 

A further Quaternary phenomenon mentioned earlier in this section is 
observed in many of the ranges which border upon an area to the south, 
and extend thence down to the Mexican boundary. I allude to a steep 
talus-slope bordering the ranges and extending at a very considerable angle 
downward to the middle of the valleys, where there is either a narrow 
drainage-line or a considerable flat valley, according to the distance apart 
of the bounding ranges and the seale of the Quaternary accumulations. It 
is obvious that where large Quaternary lakes, as in the case of western 
Nevada and western Utah, rose to a considerable height along the foot-hills 
of the ranges, the canon mouths discharged the silts of the Glacial period, 
as well as the bowlders and pebbles borne along by torrents, directly into 
the waters of the lake, where they were assorted and deposited according 
to the simple laws of sedimentation. Where there were no Quaternary 
lakes—in other words, where the valleys had a free drainage—the fine 
materials were carried on by the stream-drainage, while the coarse and 
heavy detritus constantly built up a talus at the foot of the ranges, sloping 
from the cation mouth down to the valley middle. This phenomenon is 
observed with increasing magnitude toward the south. In Oregon, in mid- 
dle California, and in the country of the Fortieth Parallel, it never amounts 


QUATERNARY. 485 


to a very conspicuous formation; but on the southern part of Toyabe 
Range, along the flanks of the White Mountains in California, and indeed 
everywhere south of the 39th parallel in southern Nevada, California, and 
Arizona, these long wash-slopes are important topographical features. 

In the general formation of cafions it is evident that their upper or 
high mountain halves have been most steeply eroded. The projection of a 
profile of a cafion bottom shows a deep, sharp curve at the head and a 
gradual approximation to a level toward the canon mouth. In other words, 
it is in the upper part of these canons (as well in gorges occupied by the 
glaciers as in those occupied by torrents) that the sharpest erosion has 
taken place. Suppose, now, that the form of the valley into which the 
mountain torrents delivered their freight was so broad and open that the 
material poured into it accumulated faster than it could be carried away, it 
is evident that there would be banked up against the flanks of the ranges 
increasingly high piles of pebble and bowlder material, and in those regions 
where disintegration greatly predominated over distant transportation the 
talus-slopes would reach higher on the range. A single condition causes 
these talus-slopes to rise highest along the mountain flanks at the mouth of 
the canons. It is, that the floods, while compressed within the narrow 
walls of the canons, are able to transport immense blocks of the rock down 
to the mouth of the canons, but at that point their waters rapidly spread 
out and immediately lose the power to transport the heaviest bowlders. 
The mouths of some of these cafions are banked up with great, sloping 
piles of bowlders, 1,000 feet high, which are not, in any sense, the result 
of débris-making forces in situ, but are actually high mountain débris 
brought down by torrents held in the narrow walls of the gorge—torrents 
which discharged their load the moment they emerged from the canon 
mouth and spread out as shallow streams. 

Along the eastern base of the Sierra Nevada these slopes are seen 
developed on a magnificent scale from Bishop’s Creek to Walker's Pass. 
But even there they are not equal to the slope of the opposite or White 
Mountain side of the valley, and farther south they are of still grander pro- 
portions. It is noticeable that in the region of the greatest glaciation these 


bowlder talus-slopes are rarely seen, and, indeed, they are in great measure 


486 SYSTEMATIC GEOLOGY. 


a southern phenomenon; whence I judge that they were chiefly developed 
in those regions which were not glaciated, but were great mévé and torrent 
regions during the Glacial period. 

The modern streams have often cut down for considerable depths in 
these talus-deposits, showing them to be made up of a variety of bowlders, 
both sub-rounded and angular. 

In the comparatively rainless regions of Nevada, Arizona, and Califor- 
nia, where these talus-slopes most abound, the cation bottoms are often abso- 
lutely dry, except in case of accidental storms or for a limited period during the 
melting of the mountain snows. The explorer often rides up mile after mile 
of canon-bed filled with fine gravels and sands, whose surface is absolutely 
parched and dry, the only water being found either by digging down to the 
bed-rock or where some outcropping ledge diverts a feeble flow to the sur- 
face. Many are entirely dry. Over the drier regions of the whole Cordil- 
leras it is no uncommon thing to find a canon from 1,000 to 2,000 feet in 
depth without a drop of water moistening its bottom. No more powerful 
commentary on the immense change of climate between the cafon-cutting 
period and the present could be recorded. Even the transporting power 
of these steep cafon torrents might have remained almost a mystery, but 
for occasional water-spouts, as they are called—immense, sudden, deluging 
rain-storms, which, at rare and exceptional moments, discharge their waters 
into one of these mountain gorges. On such occasions bowlders six or 
eight feet in diameter are swept down the cation with a fearful rush, and 
are sometimes carried out on the talus-slope for half a mile Indeed, the 
mouths of almost all the grander cafons which carry the drainage of a con- 
siderable mountain area show trains of débris with large angular bowlders 
often weighing many tons. If in the inconsiderable storms which exception- 
ally visit this rainless region at present such an immense transporting force is 
developed, it is no matter of wonder that during the period of long con- 
tinued and constant annual torrents the enormous amounts of ice-shattered 
mountain débris which rolled down upon the canon bottoms should have 
been swept out on the plain to build up these vast talus-slopes. It is 
clear that they represent a period in which the accumulation in and 


transportation through the canon exceeded the amount of material which 


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QUATERNARY. 487 


would have been produced by the erosion or deepening of the canon 
alone. 

A glacial or U cation carries bowlder-accumulations throughout much 
of its length in the form of terminal moraines. The bottom rock, when 
not covered with soil or bowlders, shows glacial scorings as far down the 
canon course as the U shape extends. 

There is no modification since the last melting out of the glaciers. 

The U part opens downward into the V part of the gorges. 

The Great Sierra or Uinta cations may have the U form for forty miles 
from the summit and then suddenly give way to the V form. 

It is evident either that there was an original V formed canton which 
the subsequent glacier occupied and modified as far as it descended, or else 
that the whole cation was simultaneously cut, the U by glaciers and the 
V by floods below the point where the ice gave out. 

Since the canons are post-Pliocene, 7. e., wholly within the Quaternary, 
the question naturally suggests itself, If the deep U gorges, often 3,000 or 
4,000 feet deep, were only modified, not actually made by glaciers, what 
torrent period was there within the Quaternary, and prior to the glaciers 
whose tracks are so fresh in the cation beds? 

As will appear later, the chemistry of the Quaternary lake basins and 
the relation of the unstratified to the stratified Quaternary materials combine 
to show two distinct periods of extensive flooding in post-Pliocene time, sep- 
arated from each other by an interval of desiccation. It seems only natural 
to correlate these two epochs of excessive moisture with the two glacial 
ages which Dawson has demonstrated in British Columbia, and which are 
so well established in Europe. From all points of view, the earlier of the 
two, marked as it was by considerable ice-sheets, was the greater ice age. 

Now, since in both ice periods the western United States was free from 
the great northern ice-field, it is possible that the floods incident and sub- 
sequent to the first ice age and its disappearance made the great V canons 
and at last obliterated the traces of the earlier mountain glaciers, and that 
in the second glacial period the trunk glaciers modified the V canons as far 
as they descended, into the U form. The actual proof or disproof of this 


hypothesis is wanting; it is quite harmonious with the known facts, and 


488 SYSTEMATIC GEOLOGY. 


seems more in accordance with present ideas of ice erosion than the other 
alternative of supposing the U gorges to be the direct sawing down of a 
rock-shod glacier. If this hypothesis, advanced here merely tentatively, 
should receive acceptance, it will be evident that the ordinary glacial mark- 
ings and moraines in the region south of latitude 48° are wholly the work 
of the second or Reindeer glacial epoch, and their extraordinary freshness 
would coincide with that view. 


Lakes oF THE GLAcIAL Pertop—A most important feature of the 
Quaternary period in the Great Basin region was the two extensive fresh- 
water lakes which occupied depressed portions of the interior drain- 
age—lakes whose former limits are indicated by singularly well preserved 
terrace-lines traced around the ancient shores. The highest of these old 
beach-lines represents a level of overflow for each lake, and beneath that 
level is a series of descending terraces which mark successive pauses in 
a general desiccation. Besides the terraces and sediments of these early 
lakes, there remain a few residual lakes of saline waters which linger in the 
deepest hollows of the bottoms of the extinct seas; Great Salt Lake being 
the most conspicuous example. Elsewhere over the dry beds and shores 
are products of desiccation and of the chemical reactions of the constitu- 
ents of the wasting lakes. 

A word as to the origin of the basins will serve to bring us to the 
direct consideration of the lakes. 

I have shown that during the Pliocene epoch, while so large a part of 
western America was covered by great fresh-water lakes, the climate was 
sub-tropical, the fauna and flora representing a condition not unlike that 
of southern Florida—palm trees and crocodiles typifying an atmosphere 
of great and uniform mildness. At the close of the Pliocene, the orograph- 
ical disturbances which I have shown to have taken place over the west- 
ern part of the United States must of themselves have produced new cli- 
matic conditions, even though the astronomical factors of the terrestrial 
climate remained the same. 

It is now clear, as first advanced by General G. K. Warren, and as 
abundantly substantiated later by myself, that the inclined plane of the 


QUATERNARY. 489 


whole system of the Great Plains received its slope by mechanical tilting 
subsequent to the deposition of the Pliocene strata. A part of that Plio- 
cene lake bed, which was over a thousand miles in length from north 
to south, is now depressed beneath the waters of the Gulf of Mexico, and 
part of its once level strata reach 7,000 feet above sea-level. Itis therefore 
clear that a change of 7,000 feet has taken place in the altitude of the 
boundary of the lake. Passing to the Great Basin, it is there seen that the 
two sides of the Pliocene lake of that region sank from 1,500 to 2,000 feet 
The lake of the Plains, after its inclination to about its present posi- 
tion, bore upon its surface a series of rivers which had free drainage to the 
sea, and during the entire Quaternary period the waters derived from the 
melting of the Glacial age in the Rocky Mountains all easily flowed east- 
ward and had an uninterrupted marine delivery. On the other hand, in 
the region of the Great Basin, the result of the subsidence of the two sides 
of the Pliocene lake was to form two interior basins, that of Utah and that 
of western Nevada, whose levels of outlet were about 5,000 feet above 
sea-level, while the bottoms of the basins were in the region of 4,000 feet. 
These two early Quaternary basins, made by the subsidence of the east and 
west edges of the Pliocene lake-bed, had, below the level of their water de- 
livery, depressed areas each about equal to the surface of Lake Huron. 
The two lakes were very nearly of the same size, but the altitudes of 
their ancient surfaces, unless they have suffered disturbance since desic- 
cation, differed by several hundred feet. It becomes a question of great 
interest to know whether, at the time of the formation of these basins, the 
Pliocene lakes, whose existence we now know by their sedimentary beds, 
were actually yet filled with water, and whether the orographical move- 
ments which outlined the new basins simply drained off the water from 
the general area into two deep hollows. It is well known that a full aquatic 
fauna of the Pliocene lakes shows that the waters were sirictly fresh At 
the same time, among the upper Pliocene beds are found horizons which 
are impregnated with alkaline salts—chlorides and sulphates. They are 
slight in extent, and not comparable with the alkaline deposits in the Qua- 
ternary. But in order to have made a saline deposit in the bottom of a 
fresh-water lake it is essential to have completely evaporated the waters. 


490 SYSTEMATIC GEOLOGY. 


The presence of these alkaliferous Pliocene beds would seem therefore to 
indicate several perhaps brief periods of desiccation during the last of the 
Pliocene age. A second argument in favor of dry basins at the beginning 
of the Quaternary is the fact that the earliest deposits on the sides of the 
extinct lake-basins are subaerial gravels, which were swept far down into 
the hollows of the basins, although probably never reaching the immediate 
bottom of the valleys. 

The phenomena of these lakes are, first, the topographical indications 
of the maximum extent and loci of outflow; secondly, the periodically grad- 
ual desiccation; thirdly, the mechanical deposits of the lake; fourthly, the 
products of successive desiccations. 

On Analytical Map VI. accompanying this sub-section are seen these 
two great Quaternary lakes restored to their former outlines, as indicated 
by the levels of their uppermost terraces. To that in Utah, G. K. Gilbert* 
has given the name of Laxe Bonnevitir. For the western Nevada body, 
I propose the name of Lake Lanonran, in honor of the gallant French 


explorer. 
LAKE BONNEVILLE. 


Lake Bonneville extended from about the parallel of 42° southward 
to 37° 30’, the meridian of 113° representing nearly the middle of the lake. 
The extreme width was in latitude about 40° 21’, where the east-and- 
west extent was 180 miles. From north to south it had a stretch of about 
300 miles. For the outline of the southern half of Lake Bonneville, I take 
the data from the map of Lieut. G. M. Wheeler, which carries the lake-area 


*Gilbert was the first to treat this lake systematically. His pages concerning it, in Vol. IIL., 
Geographical Surveys West of the 100th Meridian, do not mention his having taken for his map the 
northern part (nearly half) from the then uupubiished topography of this Exploration; but the map 
itself credits the topography to me. Doubtless the appropriation was made after the pages were 
printed. In my map accompanying this section I have taken that part of Lake Bonneville south of the 
40th parallel from Wheeler’s map, the Bonneville work thereon being Gilbert’s. In other words, we have 
each taken topography from the other; and although Gilbert has gone over and studied the great lake 
through the Fortieth Parallel area, I have kept carefully within my own lines. Gilbert’s study of the 
area and outline, and his thorough way of working out the outlet, are entitled to all praise. Since he 
precedes me in publication, I give here little space to the points he has so well discussed, namely, the 
general features and the mechanical sediments of the lake. All the points as to the sediments brought 
out by him were previously observed by my colleagues and myself, and I have only one minor point of 
difference with him, which will appear in the sequel. Avoiding as far as possible any extended repeti- 
tion of prior statements, I devote myself more particularly to tho chemical phenomena of desiccation. 


QUATERNARY. 491 


of Mr. G. K. Gilbert. For the northern half of the map, namely, north of 
the 40th parallel, the data are taken from the maps of this Exploration. 
Escalante Valley, representing the southernmost arm of the lake, was never 
examined by us, and its addition to the area of Lake Bonneville is, like all 
the south half of the lake, due to Mr. Gilbert. I have always felt some 
hesitation in considering this important basin as a part of Lake Bonneville, 
and have expected that Mr. Gilbert would finally regard it as a distinct lake 
of greater altitude, which drained north into the larger body. 

Between the 39th and 41st parallels the mountain ranges of the Utah 
Basin for the most part rose above the surface of the water and formed an 
interesting archipelago, separated by more or less shallow arms of the lake. 
The deepest hollow is represented by Great Salt Lake, which is of 
course the desiccated remnant of the fresh-water sea. The ancient high- 
water mark of Lake Bonneville is traced in the form of a very evident ter- 
race along the foot-hills of Wahsatch Range, the Promontory, all the 
islands which now rise high enough out of the lake, and indeed all the 
insular and bounding ranges within the limits of the ancient body. The 
present water-level of Great Salt Lake, after correction of the Central 
Pacific Railroad level by the addition of the error at Sacramento, is about 
4,250 feet above the sea. The uppermost terrace, which is clearly recog- 
nizable, is about 940 feet above the level of the lake in 1872, making the 
altitude of the water-level of Lake Bonneville 5,190 or 5,200 feet. 

From the 40th parallel to the northernmost exposures of the highest 
terrace, the barometer, observed synchronously, showed no appreciable 
difference of level, from which I conclude that the northward subsidence 
of land during the Champlain epoch either did not take place in this part 
of the interior of the continent, or else its effects were wholly south of the 
40th parallel. Gilbert, always keenly alert to discover any facts bearing 
on this question, inclines to attribute the superior level of the Escalante 
Valley upper terrace to a movement later than the occupation of the area 
by water. If his surmise is correct, it would be directly opposite to the 
general law of the Champlain subsidences, in which the northern, not the 
southern land was depressed. Until it shall be fully substantiated that 
Escalante Valley was a part of Lake Bonneville, and not, as I suspect, a 


492 SYSTEMATIC GEOLOGY. 


superior lake draining into it, the probabilities to my mind seem againsta 
rise of the southern part of the lake in post-Bonneville time. After the 
above was in the printer’s hands a further reference to the subject was made 
by Gilbert,* who reiterates a change of level due to orographical action, and 
if I understand him correctly he discovers two kinds of level-change, one 
due to subsidence after the manner of the Champlain depression, the other to 
strictly orographical mountain-faults, such as are described in his communi- 
cation to the Philosophical Society of Washington. 

The configuration of the country to the south of the southern limits of 
the ancient lake is conclusive that it had no outflow in that direction. But 
the divide between the Utah Basin and -the depression of Snake River falls 
below the level of the upper terrace, and it is therefore clear that the lake 
poured its waters into the valley of the Snake, and thence through the Co- 
lumbia into the Pacific Ocean. That these waters were at that time essen- 
tially fresh, is rendered probable ,by the species of fish which are in the 
land-locked streams that flow into the present dry Bonneville Basin; also 
by the remains of fresh-water mollusks found in the calcareous tufa which 
is in many places the cementing material of the gravel of the upper terrace. 
The 5,190-foot beach, or, as fixed by Gilbert, 5,178, was called by him 
the Bonneville Beach. To a somewhat less prominent but still very per- 
sistent terrace, about 360 feet below, Gilbert gave the name of Provo Beach. 

Below the upper shore-line is a series of successively lower terraces, 
indicating a gradual recession of the waters down to the present level of the 
lake. This recession is obviously due to the excess of evaporation over the 
inflowing rivers. On the subject of the outlet Gilbert has the honor of 
discovery and priority in announcement.t He stated in a communication to 
the Philosophical Society of Washington, January 13, 1877, that Red Rock 
Pass, near Oxford, Idaho, gave exit to the former overflow of Lake Bonne- 
ville, and at the same time mentioned a slight post-Glacial movement of the 
great west-face fault of the Wahsatch. Gilbert, in restating his discovery, 
has added the fact that the river channel at Red Rock Pass had cut down 
to the level of the Provo Beach, thus accounting for that feature. 


* American Journal of Science and Arts, Vol. XV., April, 1878. 
t Since the above was in type, Peale, in the American Journal for June, 1878, disputes Gilbert’s 
claim, and recalls Bradley’s mention of Red Rock Pass. 


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QUATERNARY. 493 


The mechanical deposits within the area of Lake Bonneville consist, 
as Gilbert has shown, first, of subaerial gravels washed down by flood and 
stream, and rolled down steep slopes by rain and wind; secondly, of 
the finer detrital and precipitated matters which have accumulated on the 
floor of the lake in strata of sandy, clayey, and calcareous mixture, and 
which, in the present desiccated age, are exposed, undisturbed beds, the 
greater part of whose area is uncovered by later subaerial gravels. 

The subaerial unstratified deposits were continuous or at least recur- 
rent formations, covering the whole lapse of Quaternary time over the 
bounding-slopes of the Bonneville area which were not at any time water- 
covered. It is seen that the gravel series is divided or interrupted by the 
stratified beds; in other words, that in point of sequence there is, first, a 
heavy bed of gravel, both rounded and angular, of a maximum exposure 
(the bottom being concealed) of 200 feet; secondly, the stratified sediments 
which overlap the earlier gravels; and thirdly, a latest gravel, varying from 
75 to 150 feet, which since the last desiccation has been washed down the 
basin-slopes and over the edges and a considerable area of the surface of 
the fine Bonneville strata. My observations on-all these points agree in 
detail with Gilbert’s. 

By reference to the Geological Atlas accompanying the report, it will 
be seen that east of the Wahsatch, in the region which during all the 
Quaternary age had free fluviatile delivery to the sea, the Quaternary is 
colored in one tint. It consists, besides the irregular coating of soil, the 
result of chemical and mechanical disintegration of rocks, a feature too incon- 
spicuous to show on the general geological maps, of river-bottom accumu- 
lation of no great extension. Although the eastern part of the work 
touches the Loess deposits of the plains, it merely touches them, and that in 
their least characteristic region. As I have no considerable light on the 
question, the Loess is not discussed. 

West of the Wahsatch the Quaternary is shown in two colors: one, 
denominated Lower Quaternary, is the great lacustrine formation; the other, 
or Upper Quaternary, is intended to embrace the sheet of subaerial 
gravel which is subsequent to the latest desiccation, and hence later in age 
than the lacustrine Lower Quaternary. The lowest or ante-sedimental 


494 SYSTEMATIC GEOLOGY. 


gravels are not shown on the map, from the fact that they are nearly 
always covered by the two later divisions. All these were, however, recog- 
nized in the Bonneville Basin and in that of Lake Lahontan. 

Geological Maps HI, IV., and V. show in the basin of the two great 
Quaternary lakes, and elsewhere in the area of lesser extinct contempora- 
neous lakes in middle Nevada, a wide expanse of the Lower Quaternary or 
lacustrine beds, and the still greater distribution of the most modern sub- 
aerial gravels. 

Avoiding as far as possible the repetition of Gilbert’s reasoning, I yet 
find it necessary to say here, as he has said before, that the sequence and 
stratigraphical relations of these three members of the Basin Quaternary, 
not only for Bonneville, but for the whole Great Basin region, indicate, first, 
a dry period in which subaerial gravels were washed down into basins; sec- 
ondly, a filling of the depressions with water, during whose occupation the 
stratified deposits covered the broad basin-bottoms and considerably over- 
lapped the earlier subaerial gravels; thirdly, an age of desiccation, in which 
the lake waters dried out and the Upper Quaternary or most modern sheet 
of subaerial gravel washed down over the earlier gravels and over the 
dried surface of the lake beds. There are other considerations, to appear 
later in this section, which confirm this interesting proof of two desiccation- 
epochs, and considerably enlarge our conceptions of the history of the 
period. 

The Lower Quaternary (Bonneville beds of Gilbert) contains an abun- 
dant molluscan fauna, of which the following are the most important forms: 


Limnea desodiosa 
Pomatiopsis lustrica. 
Amanicola Cincinnatensis. 
Succinea lineata. 


The latest subaerial gravels have yielded a skull of Bison latifrons and 
fragments of bones, supposed to be reindeer. 

The evaporation of such a great body of fresh water could only result 
in the concentration of the soluble salts and the precipitation of those 
whose chemical nature forbade their continued solution in the increasingly 


QUATERNARY. 495 


strong alkaline water. The uppermost terraces are made of the washed 
gravel and pebbles of a beach deposit, which in most cases are quite 
securely cemented together by a calcareous tufa. In places the entire 
material of the terrace is of more or less porous tufa, in which are enclosed 
but few rock fragments, sometimes angular and sometimes rounded, in all 
eases derived from the neighboring hill. A characteristic specimen of this 
tufa, collected on the main terrace at Redding Springs in Salt Lake Basin, 
and analyzed by Mr. R. W. Woodward, of this Exploration, is given in 
the table of chemical products due to the evaporation of Lake Bonne- 
ville. It is seen to consist essentially of carbonate of lime, with a small 
percentage of silicic acid (for the most part, doubtless, included sand, 
but also to a slight extent as combined silica), a low percentage of alu- 
mina, a trace of sesquioxyd of iron, 34 per cent. of magnesia, a little 
soda and potash, and a trace of lithia and phosphoric acid, with a constant 
minute proportion of water. The specific gravity of the tufa is from 2.4 
to 2.3. If the reader will refer to the table of the desiccation-products of 
Lake Lahontan, he will observe that the tufa of that great companion 
body of fresh water possessed, down to the minutest constituent, precisely 
the same chemical nature. 

The tufa of the Lake Bonneville terraces is a fine, compact, grayish- 
yellow mass. When acting as a cement for the terrace-beach pebbles, it 
usually occurs in concentric layers enveloping the pebbles, with the inter- 
stices filled in with a fine granular carbonate. Where it exists in solid cakes, 
as on the terrace above Redding Springs, it has in great measure the porous 
texture characteristic of calcareous tufas and travertines. In thin section 
under the microscope it presents a curious, opaque appearance, and has 
a light, earthy-gray color, carrying innumerable fine, dust-like particles, 
which are simply the mechanically entangled silt of the shore. Through 
the absolutely opaque section are cloudings of transparent material, which, 
under crossed nicols, are seen to be microcrystalline masses. The indi- 
vidual crystals are too small to display the color phenomena of calcite, but 
by the analysis they are unquestionably a fine microcrystalline lime-car- 
bonate. Considerable passages of the transparent carbonate wander in 
cloud-like forms through the more opaque material. The latter is doubtless 


496 SYSTEMATIC GEOLOGY. 


opaque simply from the mechanical suspension of minute mineral particles. 
Organic matter like the roots of water-plants, as well as minute mollusks, 
is enveloped in the mass. One peculiarity, as seen under the microscope, 
is the development of concentric circles, which are defined by a banded 
arrangement of the included foreign particles, or by the spherical arrange- 
ment of a homogeneous, gray, cloudy material, the origin of whose opacity 
is unknown, since the highest power of the microscope fails to resolve it. 

In the table of analyses of this lake is given also the composition 
of the present water of Salt Lake, which is seen to consist essentially of 
chloride of sodium, sulphate of soda, sulphate of potash, sulphate of lime, 
and chloride of magnesium. Among these the chlorides of sodium and 
magnesium greatly predominate, while the united sulphates of soda, potash, 
and lime reach about 10 per cent. of the entire solid material. In the 
analysis it will be seen that Professor Allen has computed all the lime as 
sulphate. It is a noticeable fact that in such a dense saline solution, one 
in which the solid matter is approximately 15 per cent. of the entire weight, 
there are none of the alkaline carbonates which are characteristic elements 
in the saline lakes farther west. 

The percentage of sulphate of lime is not too high to remain in solution, 
even in waters of far less density. Indeed, the analyses of nearly all the 
European rivers show a higher percentage of sulphate of lime in the entire 
sum of solid material than do the waters of Salt Lake. The chloride of 
magnesium, representing one tenth of the entire solid contents of the lake, 
is present in unusually high proportion. Lithia, though given in the 
analysis only as a trace, is present in sufficient quantity to give an invari- 
able reaction in the spectroscope from the contents of a single drop of 
water. 

In many respects the present solution in Great Salt Lake differs from 
that of any other saline lake. The Caspian, a far fresher water, with but 
six tenths of 1 per cent. of solid material, has its salinity chiefly made up 
of the chlorides of sodium and magnesium, with the sulphates of magnesia 
and lime; but there is also an appreciable percentage of bicarbonate of lime 
and magnesia, elements entirely lacking in Great Salt Lake. The Dead 
Sea, on the other hand, has a far higher total of saline matter, varying, 


QUATERNARY. A97T 


according to different analysts and specimens, from 14.7 to 26.3 per cent. 
of the whole weight. In the Dead Sea, magnesium chloride is the pre- 
dominating salt, according to Gmelin and Marchand. In the absence of 
carbonates, Great Salt Lake resembles the Dead Sea; but in the enormous 
predominance of chloride of sodium over all other salts, and in the entire 
absence of carbonates, it is unlike any other large lake the analysis of 
whose waters has been published. A case of even more exclusively sodium- 
chloride solution is the small lake of saturated brine which, in the rainy 
season, overlies a bed of nearly pure chloride of sodium in Osobb Valley, 
western Nevada, containing only chloride of sodium, with minutest traces 
of chloride of magnesium and sulphates of the two bases. 

At the time of the Stansbury expedition, in 1849, the level of Great Salt 
Lake was about eleven feet lower than at present, and the area of the lake 
as surveyed by him gives 1,700 square miles. From our survey we esti- 
mate 2,360 square miles of lake surface, an increase since Stansbury’s work 
of 660 square miles. The balance between inflowing waters and evapora- 
tion was about even, showing only slight oscillation from before Stansbury’s 
time till 1866. From 1866 to the present, a slight climatic oscillation has 
occurred, by which the influx of waters is in excess of evaporation, and hence 
the level of the lake has risen about eleven feet, covering a wide expanse of 
lowland, and making its greatest encroachments westward over the nearly 
level floor of the desert and northward over Bear River Bay. In conse- 
quence the solution has been diluted, from a point where, according to the 
analysis of Dr. L. D. Gale,* the water yielded of solid contents 22.4 per 
cent., to its present low density. Gale’s analysis is evidently at fault in 
showing no sulphates of potash and lime. From the analysis of the present 
water it is evident that the carbonate of lime, almost invariably the predom- 
inating salt of all heretofore examined rivers, is less soluble in the presence 
of a strong alkaline solution like the modern Salt Lake than it is in pure 
fresh water; while the sulphate, nearly always inferior to the carbonate in 
river waters, is able to remain in solution in the presence of sulphate of 
soda and the chlorides of sodium and magnesium. In consequence, the car- 
bonate of lime which is continually poured in by the rivers is promptly pre- 


*Stansbury’s Exploration and Survey of the Valley of the Great Salt Lake of Utah, 1853, p. 419. 
32 K 


498 SYSTEMATIC GEOLOGY. 


cipitated. That these waters also refused to hold in solution the carbonate 
of lime when they were comparatively fresh, is proved by the important 
deposits of calcareous tufa upon the upper terrace. Had the waters of the 
lake at the time that it possessed an outflow been exactly like those of the 
rivers, it is difficult to see why the carbonate of lime which they introduced 
should have crystallized out in the form of tufa; but at the time of its 
greatest expansion the lake no doubt contained a great number of hot 
springs, swelling the flood with both alkaline and calcareous solutions. In 
the presence of these salts the carbonate of lime went down; and while the 
fresher lake contained sufticient carbonate of lime to furnish the material 
for the tufa terraces, the more concentrated waters of to-day are absolutely 
free from that salt. The same phenomenon is constantly observed near the 
mouths of rivers which deliver into the sea, where the carbonate of lime 
brought down by the fresh streams is deposited in the form of a fine erystal- 
line precipitate, which is seen in the deltas cementing the sand and gravel 
of the estuary. 

While the tufa represents the insoluble and the present lake waters 
the soluble portions of the contents of Lake Bonneville, there are upon 
the desert plains in the neighborhood of the lake, residua of evaporation 
which during the annual rainy season soak down into the Lower Quater- 
nary beds, and during the dryer months by capillary attraction are drawn 
to the surface and dry, leaving glistening saline efflorescences, which are 
of great effect in the peculiar arid landscape. The valley of Deep Creek 
sends down a small stream bearing the drainage of a valley which in gen- 
eral is lifted entirely above the level of Lake Bonneville. The creek waters 
flow out and gradually evaporate over the Quaternary beds At the point 
of sinking, the ground is more or less covered with a white efflorescence of 
no great thickness and of variable purity. A specimen collected was ana- 
lyzed by Mr. Woodward, and the result is given in analysis 24 of the 
Bonneville table. The insoluble portions are the sand and gravel which 
are unavoidably collected with so thin an efflorescence. The salt consists 
essentially of chloride, carbonate, and sulphate of soda and potash; when 
theoretically combined giving 38.25 of chloride of sodium, 37.09 of carbo- 
nate and bicarbonate of soda, and 17.54 of sulphate of soda, with 4.71 of 


QUATERNARY. 499 


sulphate of potash. The salt in this basin collected by us is peculiar as 
containing the only carbonate of soda which we have observed within the 
area of Lake Bonneville. Analysis No. 25 is of the efflorescence upon the 
lower Quaternary beds of the Great Desert, between Granite Peak and 
Cedar Mountain, on the old Overland Stage Road ; and as it occurs in con- 
siderable thickness, often an inch or an inch and a half, the specimen is 
remarkably pure, having 97 per cent. of soluble matter. It is essentially a 
normal chloride of sodium, yielding upon analysis 99.37, with a slight 
admixture of sulphate of lime, amounting to only about two tenths of one 
per cent. 

At the southern extremity of Promontory Range, the Archzean siliceous 
and argillaceous schists, coming down nearly to the water's edge along the 
eastern shore, present a cliff nearly 50 feet in height of dark shaly schists, 
dipping about 25° to the west. The whole cliff is deeply shattered and 
seamed with interlacing fissure-lines, and the rocks are variably decomposed 
and coated with a white aluminous efflorescence. Dr. Gale, in the Stansbury 
report, gives an analysis of this alum, and classifies it as manganiferous.* 
Prof. J. Lawrence Smith+ also gives an analysis of the same alum, having 
crystallized it from an aqueous solution. Mr. Woodward’s analysis of the 
salt collected by us gives sulphate of magnesia 57.07, sulphate of iron .87, 
sulphate of alumina 37.48, sulphate of potash .37, chloride of sodium 3.04, 
and excess of sulphuric acid 1.17. It will be seen that this differs from the 
analyses of Professor Smith and Dr. Gale by the absence of manganese, 
and the very small percentage of iron, which evidently replaces it. The 
specimen collected by this Exploration was obtained twenty-two years after 
the former, and probably there has been a radical change in the character 
of the salt. The analysis as given by Mr. Woodward makes the mineral a 
richly magnesian alum, with a little chloride present as an impurity. It is 
rather a pickeringite than a bosjemanite, which was clearly the salt analyzed 
by Professor Smith. 

Copious springs, rich in chloride of sodium, with a little sulphate of 
soda and sulphate of potash, flow out from under the limestones along the 


* American Journal of Science and Arts, Vol. XV., 1853, p. 434. 
tAmerican Journal of Science and Arts, Vol. XVIII., 1854, p. 379. 


500 SYSTEMATIC GEOLOGY. 


eastern base of Promontory Range, and add their salts to the already 
strong chloride solution of the lake. 

Upon the old Overland Stage Road, west of River Bed Station, was 
a stage-house known as Dugway Station. Analysis No 27 is of the salifer- 
ous strata of the upper Quaternary, taken from two feet below the surface 
in a ravine near the station. It is essentially a fine but gritty sand 
deposit, with a soluble salt distribution through the interstices. It only 
contains about five per cent. of saline matter. The analysis yields 86.33 of 
chloride of sodium, 1.05 of sulphate of soda, 9.11 of sulphate of lime, 1.9 
of sulphate of magnesia, with a small excess of sulphuric acid. The sur- 
face of the desert, made up of a loose, calcareous, clayey soil, mixed with 
a good deal of fine sand, was also examined chemically. The result in 
analysis No. 28 shows that there were but five tenths of 1 per cent of soluble 
matter, and the main portion of the insoluble is sulphate of lime. A little 
chloride of sodium and an unimportant amount of sulphate of magnesia make 
up the soluble part. In other words, from the surface-soil has been leached 
out the greater part of the soluble salts, while from the strata a few feet below 
is obtained a sample having eight times as much soluble matter, and that 
chiefly made up of chloride of sodium and sulphate of magnesia. 

Along the base of Wahsatch Range, at Salt Lake City and north of 
Ogden, are important hot springs pouring a large volume of heated waters 
into the lake drainage. They contain sulphuretted hydrogen, carbonates of 
lime and magnesia, sulphate of soda, and chloride of sodium, the latter 
being in all cases much the largest factor. South of Utah Lake the bed of 
the ancient lake has not been examined by this Exploration. 

From a qualitative examination of numerous salines, besides those whose 
quantitative analyses are given in the accompanying table, it seems that 
the predominant salts of this whole basin are chlorides of sodium and mag- 
nesium, with sulphates of soda, lime, and potash, the latter always in much 
less quantity than the chloride salts. The efflorescence at the sink of Deep 
Creek is the only alkaline carbonate observed; and even if in the localities 
not visited by us there should be found other sources of alkaline carbonate, 
they must remain as exceedingly unimportant and exceptional salts in this 
basin. It is essentially a chloride basin, with the addition of a moderate 


QUATERNARY. 5Ol 


amount of sulphate salts. It would seem that the carbonate of lime, which 
is now brought in by the present drainage, either goes down as a crystal- 
line precipitate of carbonate, or decomposes some of the sulphates and 
remains in solution as sulphate of lime, of which the present waters bear 
.85 solid in 1,000 liquid grammes. Interesting spherical carbonate of lime 
sands are observed at several points on the beaches and lake bottom, 
notably near Black Rock on the west shore of Promontory and on Bear 
River bay. Under the microscope these globular sands are seen to possess 
a concentric structure, the layers made up of what appeared to be crys- 
tallites. From the numerous chloride and sulphate springs within this 
basin, it is clear that, although now the lake is very concentrated, the 
present constituents have been the predominating ones as far back as we 
have any chemical clew. While it is well known that in process of time 
there is a change in the chemical products of springs, yet there is no local 
reason to suppose that in this case they have been other than chloride and 
sulphate springs. In the case of Lake Lahontan, as will be shown later, 
there has been a great chemical change in the character of the salinity, but 
there is no reason to infer that a parallel change has taken place in the 
Bonneville area. 

The desert efflorescences arise from strata which were thoroughly 
impregnated with the salts of the lake at the time of its desiccation, and 
which come out upon the surface in the dry months, and during periods of 
rain are partially drained into the lake and partially soaked back into the 
strata. To the springs and to the rivers which flow into the lake we must 
look for the true source of supply of the ingredients of the lake ; and while 
the prominent salts of the rivers are carbonates and sulphates of lime, those 
of the thermal springs are chlorides and sulphates of the alkalies. To the 
rivers, therefore, are due in great measure the tufaceous material and limy 
sand, while to the springs are probably due the alkaline properties of the 
lake. The saline zones seen at points in the Pliocene strata, although they 
never possess a high percentage of soluble matter, are sufficient to indicate 
periods of desiccation during the Pliocene, or, in other words, oscillations 
in the dryness of climate quite analogous to the two dry ages shown by the 


subaerial gravels of the Bonneville area of Utah, which has been the theatre 


502 SYSTEMATIC GEOLOGY. 


of two or more periods of important desiccation, with an accompanying 
concentration of solutions. 


A few alkaline incrustations in middle Nevada, outside the limits of the 
two great Quaternary lakes, are of some interest and are given here in table 
of chemical analyses No. IV. In the same table are included for convenience 
some hot-spring products which will not be specially mentioned. 

Among the more interesting salines, the following may be particularly 
noticed : 

Clover Valley, which lies directly east of the highest part of the Hum- 
boldt Mountains, carries the well known Eagle Lake, and receives the drain- 
age of a considerable area. Some of the streams which flow from the 
mountain into this basin sink into the gravelly Quaternary, and always, 
during the dry, warm season, there is a limited amount of saline efflores- 
cence at or near their sinks. A specimen collected by us shows an amount 
soluble in water of 37.8 per cent. Under analysis, it proves to be com- 
posed of 24.96 of chloride of sodium, 39.04 of carbonate and bicarbonate 
of soda, and 33.88 of sulphate of soda, with a trifle of sulphate of potash. 
It will be seen that this mixture of chloride, carbonate, and sulphate is the 
characteristic mixture of the lakes of western Nevada, and the high per- 
centage of carbonate already shows a change from the Bonneville area. 

On the west side of Humboldt Range, in the valley of the North Fork 
of the Humboldt, near Peko, there is also an alkaline efflorescence which 
permeates the sandy soil of the flood-plain of the river. This saline matter 
is a seepage from the alkaliferous strata of the Pliocene which covers a 
great portion of the country drained by the North Fork of the Humboldt. 
These sands, as collected, contain 53 per cent. of soluble matter, of which 
only a small proportion (74 per cent.) is chloride of sodium, while there 
is the unusually high proportion of 834 per cent. of carbonate and bicar- 
bonate of soda, with 4.6 per cent. of sulphate of soda and 4.4 per cent. of 
biborate of soda. These salts, the result of carbonate and borate springs, 
have impregnated more or less of the Pliocene strata on both sides of the 
river; but this is the most typical and richest of the carbonate efflorescences 
of this region. 


Locii gS 
| 


Number of 
analysis. 


i) 
as 


Sink of Deep Cre\. 


Great Desert, bety ; 
and Cedar Mou. 


25) 


26 | Alum Bay, Utah |7.07 


7-01 


27 | Dugway Station, 1.71 
road, Great Des\; .go 
below surface. 


28 | Surface, Dugway 


a 


Fe Si S| Total. 
0.04 | 99-65 
0.13 100.03 


0.87 | 37-48 | 1-17 | 100.00 


0.83 | 37-25 | 1-21 | 100.00 


0.05 | 99-00 
0.58 | 98.97 


Loca 


Number of 
analysis 


| 
29 | Main Terrace, Re 
Lake Desert. 


Loc ‘a Ss 


Number of 
analysis. 


| 


30 | Salt Lake water* 


MgCl Cl Total. 
Excess. | 
858 14.908 -862 | 149.940 


TABLE OF CHEMICAL 


ANALYSES. 


III—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. 


DESICCATION-PRODUCTS OF LAKE BONNEVILLE. 


Saline Effllorescences. 


< 
= ina | i a 
Locality. Analyst. Ca | Mg | Na | Na |] K K} | Cl Cc S ae Total.} Na Cl|Na C+-C] Na§| KS | CaS 
aia aunce|| Eat. oO 
2 = carbonate. vo 
24 | Sink of Deep Creek - - - - -|R.W. Woodward 26.47 | 16.50) 2-55] . |} | 23.20 4-91 13-36] 12-05] - -| 99.04} 38-25] 37-09 | 17-54] 4-71 
26.39 | 16.37 | 2.51 || - 23-14 5:00 13-36] 11-9r} - «| 98.68) 38.14] 37.17 | 17.37) 4.63 
25 | Great Desert, between Granite Rock se 97-00 0.10 39-06 | tr. : 60.31 nee - -| 018] . . | 99-65} 99.37 0.24 
and Cedar Mountain, 97-00 0.09 . 39-28 | tr. 5 60.49 60 : +} 0.17] . . |100.03} 99.68 0.22 
Al, O; 
26 | Alum Bay, Utah - - - - - - “ 26-55 |0.35 x26 19.02] . =| 2.24) 0.2 1.85 Gas - + | 64.96] 0.04 |100.00] 3.04 0.37 
A 23 
36-55 }0.33| 11-18 | 19.00] . .| 2.16) . .| og 1.86 b 0 + «| 65.41 | 0.06 |t00.00} 3.05 0.65 
27 | Dugway Station, Overland stage- ss 4.83]. 3:84] 0-57) - - | 34.56 | tr. 0 | 52-53 0 9 + +| 7-37] 0-214] 99-01] 86.61 mete I-31 9:32 
road, Great Desert, Utah, two feet 4.83 |. 3:76 | 0.63] - . | 34.88) tr. | 52-37 & 0 - .| 7-21] 0.12 | 98.97] 86.33 fon 1-05 g.I1 
below surface. 
28 | Surface, Dugway Station - - - ce 00.50 31.22] 1-84] - «|| 9.54 9-78 bito - - | 45-60] 0.54] 97-44 : 
00.50 30-87 | 2.41 - =| 9-20 - {| 10.81 o 9 - . | 45-48] 0.50 | 98.27 . 
= 1 
Thinolite (fseudo-Gay-Lussite). 
Gy j s 
bar | Specifi 
5h ie. s re: cen 4 5 5 4 “ : 5 pecific 
aa Locality. Analyst. Si At ¥e Ca | Mg | Na K hi H C | Total. gravity. 
ie | 
= 
29 | Main Terrace, Redding Spring, Salt | R. W. Woodward | 8.40* | 1.31} tr. | 46.38] 3-54] 0.48] 0.22 ir. PO* tr. | 1-71 | 38.20 | 100.24 | 2.4, 2.3, 2.4 
Lake Desert. 8.22* | 1.20] tr. | 46:50)! 3.525) (0.54 || O.22 3 BOF itr. 91.62) |/48:43) coord) eee 
* Combined (silicic acid and sand. 
Lake Water. 
= = ee 
3 a 
ade ( 4 : afl Bee Specific ras 
2@ Locality. Analyst. Ca Mg Na K cl 4 B Pp ae Total. ae NalGly | 9 Naish) Ks aS 
pd fens 6 
30 | Salt Lake water* - - - - - -|0,D, Allen- - | +3570 | 6.301 | 66.978 | 2.901 | 83.946 | 8.2115 tr. tr. 18.758 | 149.940 | 2.4,2.5 | 118.628 | 9.321 
| 


*Solid grammes in 1000 grammes’ weight of water. 


(EEE IE 


ae | Z 
vu 
tali|K Cll K'$|Ca CljCa SMgcl Si |y Total. 
99-42 
| | 
CO? | 
. | 1-94] 0.43 | 100.25 


Nigfitgy cr "5, oe fox peo) eas Camo (RC Ab eee eee Les + | 100.21 


| | Na 
} . 0.88 . «| 11-94 6.31) BSN a foie alo. cal 1:53 100.89 
| Na 
aie 0.87 ae 201 5-84] 8-55 | 5 Allg ela oll cetefss || skeresui©) 
Ip | | 
aillc <c 9-14 | | © 63 | 99-83 
alters | 9-32 0-74 | 99-53 


| | 
( | GS | | 
a ey 
3 | | 
| | lo 13] 0-52| | 100.00 
| | | 
3 | ees pesOs.| 
| Sol cc | 2.77 s\@outel|a oo oll Tash lh Hers 


ao elie al ov eio olle ells of) o pulse 


a iealeet calla ese sie? iae|iss~ .. | 101-05 


TABLE OF CHEMICAL ANALYSES. 


} 
| 


| 
IV.=UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEI 


Salines and Hot-Spring Products. 


sued 
Na Cl] NaC 


ss .| ros Gi | | j é Bs z | 
aS ag as "i F 3 oy re a ag |} oe |) ae a 2 Be, | 
22 Locality. Analyst. 5s Te Ca |Ca|Mg|Mg] Na | Na k Ke} 1) Cl = uc SS, 8 aes ost | H a Se | Total. 
3 | EE | ee eS | eke aE 
= { | || ; a eee 
i | i 
31 } Cortez Valley - - - - - - -|0.D.Allen- -| tr. mile 4 : in : i lie | eet 
(Effiorescence.) i | } | | | | | 
| Clover Valley - - - - - - -|R.W. Woodward | 37.80 35:66} 9-79 164 0 15-15| 3:35 | 15-27 19-99| ioe |) te, Bie 100.25] 24.96 
(Efflorescence.) | | | 
33 p North Fork Humboldt Peko - | us 53-00 40.81] 2.97} - |. 5 4-58| 10.07 | 30.78) 2.59] 2-41 ails | | 100.21 
(Efflorescence.) {| : | 
34 | Alkali Flat, Humboldt Valley - - a 16.40 6.16 2.22 29-62 | 6 |. 0.46) | 57-97 «| 3-72) - 5 . 0-74 100.89 
(Efflorescence.) | i | | 
| 16.40 6.08 2.16) . 29-45 0.46) 57-85 =) 3-44) 0.68 | 100.10 
35 Spalding’s Salt Marsh, Smoky Val- ns 92.00 : 35:90 | 4-94| - 54-62 4.37] - 99:83 
ley Flat, Nevada. | 92-00 Douce 35-82 | 5-04| - 54-27 4-40) - 99:53 
(Efflorescence.) | | 
| | { | 
6 | Hot Spring, Ruby Valley - - - us 1-75 | 0.80] - 1.06 0.27 ‘ - | 88.79] 7-33 
(Incrustation.) I-74 | 0.82]. ; =) |. ol ee Seen 
| 
| | 
37 | Hot Springs, Humboldt Range - | O.D. Allen - - Allis tr. 
| (Incrustation.) 1} 
38 | Hot Springs, Humboldt Range — - | w 1.17]. 9-87 28) . 2.32 53-23 0.10 0.52 
(Incrustation.) | | 
! 
39 | Hot Springs, Humboldt Range - oe 4:23 |10.20|]. .|2-48])|. 12.36) af 3:40 4-91| 16.69) - + | 42.04) . 
(Incrustation.) | 
| ~~ 
40 | Hot Springs, Ruby Valley - - - | R.W. Woodward) 57.86 50-46] 0.84) 1.53 tr. | 1.29 29-22 | 17-43 tr. 
| : (Efflorescence.) ; \ ~D~- 
. 57-86 51-10] 0.64] 1-45 | - tr. 0.99 29.30 17-57 - 
Ai+e , re > 
41 Steamboat Springs, Geiger Grade - us 0.80 | 0.14]. 0.0 °. 18 tr. - |92-67| 5-45] . 
(Incrustation.) A+Fe 2 5 75 ss d Q 7) 5:45), 
0.65 | 0.18 0.05, 0.99 0-15 tre - (92-76) 5-47]. . 
; At+ie | 
42 | Steamboat Springs, Geiger Grade - se 0.72 | 0.41 tr. tr. + |go-11| 7-56) « 
} (Incrustation.) AL+Fe ; i 
| 0.53 | 0.33 tr. | tr. | - | 90-42) 7-55 
| | ie | ~~ 
43 Sediment from Hot Springs, Reese i ui! eH 8.98 r tr. | 238 
| River Valley. | et reg: Oh r 0:38 
(Incrustation.) + 0.42 | 48.98 0.96 tr. on, 
| | 
| 
44 Hot Spring, Grass Valley - - - a - | 0.26 | 48.32 3:98 “i 
li ' 13:9 a He Io 
(Incrustation.) 5 0.12 |48.26]. . |4.11 =} th): 
ee 


T 


Na C+C} NaS} 


21.11 
39-04 | 33-88) 
{ 


83-57 | ada 4 


QUATERNARY. 503 


In Diamond Valley, between Diamond and Pinon ranges, is a remark- 
able exposure of the Lower Quaternary, being the bed of an extinct lake 
composed of strata of sand and clay of excessively fine material. During 
the wet season, and at times throughout the whole year, there is still a 
shallow lake near the northern end of the valley, which is a strong solution 
of sulphate, carbonate, and chloride, in which, however, the carbonate pre- 
dominates over the sulphate, and at times equals the chloride. During the 
drier seasons the whole of this broad alkali flat, for a distance of ten or 
fifteen miles, is a clean, hard, white sheet of alkaline and calcareous clay, 
which upon drying receives a glaze like hard-finish, and indeed is almost 
as hard as the plaster upon a wall. Heavy teams driven across it scarcely 
leave a wheel-print, and the sun reflects from it as from a marble pavement. 

In Crescent Valley, between Pinon Range and Shoshone Peak, is an 
area of wet clay and quicksand, which receives the drainage of several 
saline springs, and bears upon the surface in the drier portions of the year 
a variable incrustation of salt. This is almost a pure chloride, with a very 
little sulphate and carbonate. Owing to the influx of the saline springs, 
this whole clay is kept in a very soft and plastic condition, and, as there is 
no outward drainage, the salts accumulate and stand during the moist 
periods in pools of saturated brine. The salts of nearly all these predomi- 
nant chloride deposits are used for commercial purposes, chiefly for the 
chloridizing of silver ores. 

East of Toyabe Range, in Smoky Valley, there is a prominent 
depression, formed of Lower Quaternary stratified clays, which receives 
the drainage of the mountains on both sides, and is a wet, marshy clay- 
bed during winter, and a hard, smooth, alkali flat during summer. At the 
northern or lowest portion of this alkaline plain there is a region of reason- 
ably pure chloride of sodium, which is derived from the evaporation of 
saline springs that pour their water into the valley. The salt proves to 
have 90 per cent. of chloride of sodium and a little over 9 per cent. of 
sulphate of potash. 

Interesting hot springs occur in the northern part of Ruby Valley, 
between Frémont’s Pass and the Overland Ranch. They are essentially 


like the Icelandic geysers, depositing a tufa which is about 90 per cent. 


504 SYSTEMATIC GEOLOGY. 


silicic acid, with small additional percentages of sesquioxyd of iron, lime, 
soda, and potash. ‘These hot springs, besides depositing a large amount of 
pure white siliceous geyser tufa, discharge waters carrying more or less of 
the carbonates of potash and soda, which pass into Ruby Lake, a shallow 
body of water occupying the trough-like depression of the valley. The 
lake is predominantly a carbonate one, but it is of such a weak solution 
that fish are able to live there. All the spring waters of central Nevada, 
with the few exceptions of those having their origin in granite, are strongly 
impregnated either with salts of lime or with those of the alkalies. 

Humboldt and Reese rivers, like almost all modern rivers, carry car- 
bonate of lime in excess over all other salts, but all the Nevada rivers have 
also a variable amount of free alkaline carbonates. On entering the brackish 
lakes at the sinks of these rivers, the carbonate of lime mainly goes down, 
and the alkaline carbonates, chlorides, and sulphates remain to enrich the 
saline solution. 


LAKE LAHONTAN. 


Already, in the account of the Tertiary, it has been shown that at the 
close of the Pliocene period the lake which stretched over the present area 
of the Great Basin suffered disturbance, its two sides subsiding to form two 
new deep basins. The depression of Lake Bonneville extended from lati- 
tude 37° 30’ to latitude 42°. The corresponding depression of the west of 
the Great Basin lying at the east side of the Sierra Nevada extended from 
latitude 41° 30’ southward to about the same latitude as the southern 
waters of Lake Bonneville. The general area of the lake was somewhat. 
less than that of the Utah depression, and its altitude also was a few hun- 
dred feet lower. As the widest area and deepest depression of Bonneville 
Lake were under the bold heights of the Wahsatch, so in the depression in 
western Nevada the greatest depth and the greatest width are opposite a 
high group of the Sierra. 

To the western Nevada and California Basin I have given the name 
of Lake Lahontan, in honor of the French explorer. There is no single 
large sheet of water like Great Salt Lake in the present desiccated bed 
of Lake Lahontan, but there are several considerable bodies whose united 


QUATERNARY. 505 


area is about equal to half the present lake surface of the basin of Bonne- 
ville. Walker, Carson, and Truckee rivers carry the eastward drainage of 
the Sierra Nevada and flow into the west side of the old Jake basin. The 
Humboldt enters it from the northeast and flows for over a hundred miles 
within its former boundaries. 

A very considerable part of the area of Lake Lahontan was occupied 
by lofty mountainous islands which rose above the surface to heights often 
of several thousand feet. The Pah-Ute, Humboldt, Montezuma, Pah-tson, 
Sahwave, Truckee, and Lake ranges were all gathered as a great group 
of islands in the middle area of the lake. 

Southward, the shore-line was noticeable for its long, deep bays, en- 
tering the land to the east and surrounding complicated, narrow peninsulas. 
The entire beach line is well defined by a series of terraces, cut, like those 
of Lake Bonneville, in the steep, rocky slopes of the mountainous shores 
and islands, or gently excavated along the easy slopes of the inclined Ter- 
tiaries. Walker, Carson, Humboldt, Winnemucca, and Pyramid lakes, 
receiving the present influx of water, represent relics which the general 
desiccation has spared. 

One of the most interesting of the recent geographical features in this 
area was the bifurcation of Truckee River on its downward flow. Emerg- 
ing from Virginia Range, it turns a sharp right angle and flows northward 
in the valley depression between Virginia and Truckee ranges, the general 
level of the country declining to the north. The Truckee here flows in the 
bottom of a sharp cation which it has cut through the horizontal Pliocene 
beds. Northward these beds are bevelled off, and near the south end of 
Pyramid Lake the river flows out upon a plain, its banks lined with wan- 
dering groves of cottonwood trees. At the time of our first visit to this 
region, in 1867, the river bifurcated; one half flowed into Pyramid Lake, 
and the other through a river four or five miles long into Winnemucca Lake. 
At that time the level of Pyramid Lake was 3,890 feet above the sea, and 
of Winnemucca about 80 feet lower. Later, owing to the disturbance of 
the balance between influx and evaporation already alluded to as expressing 
itself in Utah by the rise and expansion of Great Salt Lake, the basin of 
Pyramid Lake was filled up, and a back water overflowed the former region 


5O6 SYSTEMATIC GEOLOGY. 


of bifurcation, so that now the surplus waters all go down the channel into 
Winnemucea Lake, and that basin is rapidly filling. 

Between 1867, the time of my first visit, and 1871, the time of my 
last visit, the area of Winnemucca Lake had nearly doubled, and it has 
risen from its old altitude about twenty-two feet, Pyramid Lake in the same 
time having been raised about nine feet. The outlines as given upon our 
topographical maps are according to the survey of 1867, and form interest- 
ing data for future comparison. 

The regions of the two great Quaternary lakes have this general geo- 
logical difference: Bonneville was an area of depression as early as the 
Eocene, but during the Miocene had free drainage to the sea; Lahontan 
was a land area during the Eocene, but during the Miocene was a lake 
basin. 

In the present desiccated period the aspect of the Lahontan area does 
not differ very greatly from that of Lake Bonneville. It is a series of 
alkaline clay plains, composed of undisturbed Lower Quaternary beds, the 
equivalent of the Bonneville clays, surrounded by more or less inclined 
regions of subaerial gravel between the actual Lower Quaternary level areas 
and the mountain foot-hills. The mountain ranges, such as the Pah-Ute, 
Montezuma, and West Humboldt, rise from 3,000 to 6,000 feet above the 
ancient lake bottom, their rugged sides for the most part bare of any con- 
spicuous vegetation, carrying upon their upper heights a few scattered 
piflon and cedar trees. Nowhere reaching to the level of perpetual snow, 
and in general either of dusky desert colors or displaying the brilliant, 
variegated tints of the volcanic series, the general aspect of the mountains 
is of unrelieved barrenness. 

The clay plains, during the dry summer months, are covered with 
efflorescences of soluble alkaline salts, which in many instances give the 
appearance of fields of snow. 

In particular, the basin of the Carson-Humboldt Sink affords landscapes 
of the most peculiar type. The various channels of Carson River are mar- 
gined by bands of intensely green vegetation, sharply hemmed in by the 
absolutely barren surface of the desert. The plains are either ashen gray or 


snowy white, and the waters of the lake reflect the colors of the sky or the 


QUATERNARY. 507 


tints of the neighboring mountains. Along the foot-hills is traced with 
perfect distinctness the old beach-line of the extinct lake, its even, hori- 
zontal terraces carved into the Tertiary slopes or escarped in the hard vol- 
canic bluffs. 

The altitude of the surface of Lake Lahontan was 4,388 feet, or about 
800 feet lower than Lake Bonneville. A cursory examination of the 
country lying north of the lake area indicates that there was no outlet 
in that direction. South of the great archipelago formed by West Hum- 
boldt, Montezuma, and Truckee ranges, with their dependencies, was a 
broad stretch of lake without islands, including the basin which now 
contains the two saline lakes of Carson River. Along the foot-hills of 
the Pah-Ute and the hills to the south of Carson River, the old beach- 
lines are exceedingly well displayed, and, wherever the slope is suffi- 
ciently gradual, the recession of the water marked, as in the case of Lake 
Bonneville, numerous terraces, indicating pauses in the general progress 
of desiccation. South of Walker’s Lake and Gabb’s Valley, the outline 
of the basin is hypothetical, and is constructed from a few barometrical 
notes afforded me by Mr. A. D. Wilson. I have never examined the region 
of a supposed outflow to the south, but a singular topographical feature, 
known as Forty-Mile Canon, south of the Ralston desert, seemed to me to 
afford a possible solution of the question of the drainage of the lake. The 
accounts brought by prospectors of Forty-Mile Canon indicate that its 
waters formerly flowed southward, and it is not at all impossible that the 
surplus of Lake Lahontan found exit through that channel and flowed 
southward along the slope of the continent. 

The valley of the Great Desert of California from San Gorgonio Pass 
southward to the Mexican line affords a close parallel to the area of Lake 
Lahontan It is far lower in altitude, its extreme depth being below the 
present tide-level. There, however, as on the mountain coasts of Lake 
Lahontan, the terrace lines are recorded in well defined beaches, and wher- 
ever the character of the underlying rock was at all calcareous there is an 
accumulation of tufa which either encrusts the surface in thick beds or acted 
as a cement for inflowing gravels, forming a shore breccia. 


As compared with Lake Bonneville, the chief characteristic difference 


508 SYSTEMATIC GEOLOGY. 


in the phenomena of terraces and shore lines is the great abundance in the 
Lahontan basin of calcareous tufas. Modern subaerial gravels have been in 
great measure washed down over the calcareous matter, but it frequently 
exists even on the broad bottom of the lake in thick accumulations— 
covering areas of several miles with a tufaceous deposit from twenty to 
sixty feet thick. As will be seen later, this tufa is of very great chem- 
ical interest, and its mineralogical nature affords a clew to the history of 
the lake. From its very great importance and its peculiar origin, I have 
taken the liberty of giving it a lithological name. Since it formed on the 
shores of the lake, I have called it, from the Greek 7s (shore), Thinolite. 


During all the Quaternary the high mountains have afforded the loci 
of disintegration and removal. Aside from the period of great cafion- 
cutting, the general frost and snow disintegration, and the recurrence of 
annual storms and floods, have swept down from the mountain flanks 
and from the canons an enormous amount of sub-angular fragmental mate- 
rial partly in the condition of fine sands, but largely of coarse gravel, 
of which the fragments vary in size from a hazel-nut to blocks of sev- 
eral tons in weight. The thickness of these deposits is nowhere seen, but 
from the manner in which they build up talus-slopes against the foot-hills 
of the mountains it is evident that there can not be less than one or two 
thousand feet in some extreme instances. 

From every mountain and range foot declines this gentle slope, the 
larger materials next the mountains, the smaller washed out to greater dis- 
tances. The uppermost gravels of this series, when traced down into 
the level desert areas, are seen to overlie the horizontal stratified sands, 
clays, and marls of the Lower Quaternary, which are an undisturbed for- 
mation of an unknown depth. In the stream-cuts which have opened 
extremely modern sections in the subaerial gravels, it is seen that the strati- 
fied Lower Quaternary overlies a considerable portion of the subaerial gray- 
els; indicating a former expanse of water during which the lake area 
encroached upward and outward over the older subaerial gravels, a final 
recession from its extreme expansion, and a subsequent pouring down of 
modern subaerial gravels over the exposed surface of the sedimentary beds. 
This is the same phenomenon which Gilbert has described within the basin 


QUATERNARY. 509 


of Bonneville. It is best shown, over the Lahontan area, in the region 
of Pyramid Lake and the flanks of Truckee and Lake ranges near their 
northern ends, where are considerable exposures of the lower and earlier 
gravels. Near the height of the uppermost terrace the gravels are largely 
cemented by calcareous tufa, as they are upon the higher terraces at Lake 
Bonneville; but in passing downward the calcareous deposits are very dif- 
ferent, the tufa occurring in enormous masses 30 to 60 feet thick, and with 
little inclusion of foreign rocky fragments. 

The broad area of Mud Lake Desert, the floor of Gabb’s Valley, and 
the clay flats surrounding the two Carson lakes are conspicuous examples of 
the larger exposures of the Lower Quaternary lacustrine clays and sands. 
As in the Bonneville region, the lower and earlier subaerial gravels show to 
such a very small extent in the exceptional modern cuts that they could 
make no feature upon a geological map. 

Organic life seems to have been much rarer in Lahontan Lake than 
in Bonneville. A few Planorbis are the only species of Mollusca we have 
found embedded in the gravels. One or two deep wells have been sunk on 
the Carson Desert, in the hope of finding a water free from the prevalent 
alkaline salts, and these display from 80 to 100 feet of Lower Quaternary 
beds composed chiefly of clay and sand, with far less of the marly or calea- 
reous matter than may be seen at the Dugway well in Bonneville Basin. 

A partial examination of the waters and desiccation-products of the La- 
hontan area has resulted in the discovery of some very interesting chem- 
ical facts. Among the waters which now enter the basin as rivers or exist 
in the form of lakes, perhaps the most interesting are those of Pyramid, Hum- 
boldt, and Soda lakes. 

Pyramid Lake has a specific gravity of 1.0027; its solid contents com- 
puted for a thousand grammes of water and expressed in grammes show : 
Chloride of sodium, 2.8871; carbonate of soda, .5384; sulphate of soda, 
2485; carbonate of lime, .0178; besides a little magnesia and carbonic 
acid. It is essentially a chloride lake, with the presence of carbonates of 
soda, magnesia, and lime, and a little sulphate of soda. The relative pro- 
portions of chloride of sodium and sulphate of soda in Pyramid Lake do not 
greatly differ from the ratio of the same salts in the far denser solution of 


510 SYSTEMATIC GEOLOGY. 


Salt Lake, but the waters differ widely by the presence of carbonates of 
soda, lime, and magnesia. The high proportion of carbonate of soda, amount- 
ing to one sixth of the total saline contents, accounts for the presence of 
the carbonate of lime. It was seen that in the solution of Salt Lake car- 
bonate of lime did not exist. That salt, as it was delivered by the inflowing 
rivers, cither suffered double decomposition with the sulphate of soda, remain- 
ing as sulphate of lime, or, as was evidently true of the greater amount of 
the carbonate, fell as a precipitate. The possibility of carbonate of lime, 
even in the small percentage which is present in Pyramid Lake, remaining 
in solution in the presence of so much chloride of sodium and sulphate of 
soda, is unquestionably to be accounted for by the presence of carbonate 
of soda. 

Humboldt Lake, which is really a mere expansion of Humboldt River, 
is a water of considerably less salinity than Pyramid Lake, having a specific 
gravity of 1.0007, with a total amount of saline matter of 88.8 solid in 1,000 
liquid grammes. It differs quantitatively from the water of Pyramid Lake 
by the inferior percentage of chloride of sodium, and qualitatively by the 
astonishingly high percentage of chloride of potassium, which amounts to 
nearly one third of the entire saline contents. In the Pyramid Lake water 
there is an excess of magnesia over the carbonic acid with which to combine 
it. In the Humboldt Lake water, however, besides the necessary carbonic 
acid to unite with the magnesia, there is an excess amounting to .0425 
of free carbonic acid, and there is also a minute percentage of phos- 
phorie acid. It is highest in the percentage of carbonates of any water 
in the basin, with the exception of the Soda Lakes north of Ragtown. 
Traces of boracie and silicie acid occur in both Pyramid and Humboldt 
lakes, and their waters also gave, under the spectroscope, a distinct reac- 
tion for lithia. 

For a detailed description of the little Soda Lakes lying on the desert 
north of Ragtown, Nevada, the reader is referred to Chapter V., Vol. II. 
The water of the larger Soda Lake is of very great interest, since from 
its dense solution at all the drier periods of the year, when the fluid 
is concentrated by natural evaporation, the mineral gaylussite crystal- 
lizes on the edges of the basin and on any bits of organic matter which 


QUATERNARY. 511 


may be floating or lying in the lake. It is a dense water, having, at 
the time of our examination, in 1,000 liquid grammes, solid contents of 
114.449 grammes, and a specific gravity of 1.0975. Although the propor- 
tion of carbonate of soda to chloride of sodium is not so high in this lake 
as in the waters of Humboldt Lake, its large carbonate tenure, amount- 
ing to 29.2482 of carbonate of soda, .0652 of carbonate of magnesia, with 
a considerable excess of free carbonic acid, makes it the most important 
carbonate water in the Lahontan area. Of chloride of sodium there are 
69.9413 grammes, and of sulphate of soda, 13.7626. Sulphide of sodium 
is present, amounting to .2384, and sulphate of potash equalling 3.6513. 
Like the Humboldt water, it has a little combined silica. It is therefore 
a chloride, carbonate, and sulphate water, in which no lime whatever was 
detected by the most delicate tests. It is interesting that in a lake which is 
especially noted for the annual production of fine crystals of gaylussite, 
there should be no trace of lime in the water. It is evidently true that 
in the presence of a high proportion of alkaline carbonates every atom 
of lime which the annual floods wash in from the surrounding calcareous 
soils is at once seized by the alkaline carbonate, and made up into 
gaylussite. Prof. O. D. Allen, of Yale, who executed the above analyses, 
also made a careful examination of the solubilities of Nevada gaylussite 
in clear water and in weak carbonate solutions. The mineral was 
readily acted upon in the presence of sulphates and chlorides and a 
small proportion of carbonate of soda. It retained its integrity only in 
solutions with a considerable excess of alkaline carbonate. An examina- 
tion of the evaporated salt is given in the table of analyses No. V. of the 
desiccation-products of Lake Lahontan. The gaylussite itself yielded 
19.19 of lime, 19.95 of soda, 29.55 of fixed carbonic acid, a trace of 
sulphuric acid, 31.5 of water, and .2 of insoluble residue, which was 
altogether small particles of sandy material; the water percentage being 
a little higher and the insoluble residue a little lower than the analysis of 
Boussingault given in Dana’s Mineralogy. The artificial production of 
gaylussite by Fritsche, requiring an enormous excess of carbonate of soda, 
is thoroughly in keeping with the chemical reactions of the Soda Lake 
water. It is interesting to observe that all the forms which crystallize in 


512 SYSTEMATIC GEOLOGY. 


this lake are thin in the direction of the orthodiagonal, producing short, flat 
crystals, like Figure 607 in Dana’s Mineralogy. 

The occurrence of these two lakes is so peculiar and interesting as to 
demand more than a passing mention. The surface of the country in their 
neighborhood is about 4,000 feet above the sea-level, and is formed of the 
level beds of Lower Quaternary strata, here consisting of sandy clays, 
having a surface which has been modified only by eolian erosion and the 
slight effect of rains and storms. The two basins lie within an eighth of a 
mile of each other, and they are almost exactly circular, the larger having a 
bank varying from 85 to 150 feet in fine perpendicular walls, and a diam- 
eter of about five eighths of a mile. The smaller lake occupies a similar 
crater-shaped basin, its banks having a height of from 50 to 70 feet, 
and at the date of its highest water the diameter is hardly more than 
one fifth of a mile. In the smaller lake during the drier periods of the 
year the solution becomes very dense, and a considerable part of the 
bottom of the lake is laid bare, with a thick incrustation of trona over 
the exposed portion. Neither basin has an outlet. The larger one is fed 
by a cool fresh-water spring on the northwestern side, which pours from 
a gravel stratum just above the lake. The formation of these depressed, 
funnel-like hollows in the middle of a Quaternary desert, having no out- 
ward drainage, and only varying in their density according as the humid or 
the evaporating period advances, is not altogether easy to account for. 
The presence of much basaltic material on the banks and narrow margin of 
beach, and the circular, erater-formed depression which the lake occupies, 
lead us to suspect that during the period of the occupancy of this region 
by Lake Lahontan, when the Lower Quaternary beds were in process of 
accumulation, and when there were at least 500 feet of water over the 
present surface, these crater-like lakes were points of extremely powerful 
springs, deriving their great activity from volcanic sources. 

Extremely powerful springs are now observable, coming to the surface 
from very great depths in the strong alkaline solution of Mono Lake. That 
water, besides being densely charged with alkaline carbonates, is also charac- 
terized by the abundant presence of borates, its solution being far denser than 


any of the considerable lakes of the Lahontan area. Rowing on its surface 


ft 


QUATERNARY. 513 


in a boat of considerable size, over water of a depth of more than a hun- 
dred feet, I came upon strong springs of rather fresh water, which rose above 
the level of the lake in low mounds, and this constant fountain-like pro- 
jection of fresh waters above the surface was strong enough to deflect the 
boat from its course. The diameter of some of these cold-water mounds 
was from 100 to 150 feet. A jet like this evidently necessitates a very 
powerful pressure of water at the lake-bottom, where the spring emerges 
from the sandy material of the floor. If from any cause the basin of Mono 
Lake, which is now covered with fine lacustrine muds, should be exposed 
by the desiccation of the lake, and the great spring jets cut off from their 
source of supply, on the horizontal beds which are now accumulating over 
the bottom would undoubtedly be found crater-like basins similar to those 
of the alkaline lakes near Ragtown. 

Plate XXVI. in this volume gives a very correct idea of the general 
appearance of the larger Ragtown lake, showing the high, steep banks, 
with the beach-line underneath them and the lower banks on the left. 
The smaller lake is shown in Plate XXII., Volume II., where the trona 
fields may be seen on the partially dried lake-bottom. In later pages it 
will be seen that an enormous amount of alkaline carbonate must formerly 
have characterized the waters of one period of Lahontan. The origin of 
these alkaline carbonates is among the most difficult of the chemical prob- 
lems of the region. That this carbonate was not a result of the organic 
decomposition of other salts, will become evident from a glance at the 
enormous quantities involved. Only a very few of the thermal or cold 
springs of the whole Great Basin country are now delivering carbonated 
alkalies. The hot springs of Ruby Valley, which deposit a liberal incrus- 
tation of geyser silica, yield a considerable proportion of carbonate of 
soda. It is not improbable that the Ragtown lakes, with their dense car- 
bonate solutions, represent the relics of a once copious source of the salt. 

Among the efflorescences found upon the desert, that at Magg’s Station 
on the Truckee desert is nearly pure chloride of sodium, only varied by 
less than 2 per cent. of sulphate of lime. At Hardin City, however, in the 
Black Rock region, the efflorescence of the ereat Mud Lake desert yielded 


in 100 parts, 18.47 of chloride of sodium, 52.10 of carbonate of soda, with 
33 K 


514 SYSTEMATIC GEOLOGY. 


27.55 of sulphate of soda. This is the only instance of a considerable area 
of efflorescence, in which the alkaline carbonate exceeds the united chlorides 
and sulphates. At the sink of Quinn’s River the efflorescence contained 
chiefly sodium chloride, varied only by sulphate of soda and lime. A sim- 
ilar salt, with a higher proportion of sulphate of lime, occurs as an efflo- 
rescence through the alkaline earth near Buffalo Station. From the lesser 
Soda Lake near Ragtown comparatively pure trona is taken, having a com- 
position of 40.77 of soda, 37.88 of carbonic acid, with a little chlorine and 
sulphuric acid, and 20 per cent. of water. 


I have already remarked that the most interesting chemical result of 
the desiccation of Lake Lahontan was the enormous deposit of thinolite 
tufa. In the immediate foot-hills of some of the higher ranges, the terraces 
and slopes, thickly incrusted with a gray coral-like material, are covered 
over with the most recent subaerial gravels. This is particularly the case 
along the Osobb Valley, which lies between Augusta and Pah-Ute ranges. 
So, too, along the slopes south of Carson Lake, on the divide between 
Jarson and Walker basins, much of the thinolite surface is covered with 
extremely modern gravelly detritus, but here and there along those slopes, 
wherever the topography was steep enough to preserve a rocky front, the 
crusts of gray and whitish tufa are still uncovered. Even along the flat 
bottom of the desert, at elevations of about 4,000 feet, there are long reefs 
covered with the tufa, which rises in most peculiar and fantastic forms, stand- 
ing up often in cylindrical chimneys, having an obscure, partly obliterated 
tube in the axis. Some of these chimneys are ten and twenty feet in height. 
For the most part thinolite has an extremely rough, ragged surface, full of 
intricate interstices, rarely in the region of Carson Lake showing any consid- 
erable exposure. In the region of Humboldt Lake, on the slopes of Monte- 
zuma Range, it is nearly overwhelmed with modern débris, but along the rail- 
road are a few rocky ledges covered with coatings five to ten feet thick of tufa. 
Single isolated groups of fantastic forms occur southwest of Oreana, rising 
above the Quaternary plain, which is based upon the horizontal Tertiary 
of the Humboldt group. Along the slopes of Pah-Ute Range which face 
the Carson desert are but few traces of thinolite; but on the south foot of 


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QUATERNARY. 515 


West Humboldt Range, which directly overlooks Carson Lake, the upper 
terraces show considerable incrustations, never, however, over five or ten 
feet in thickness. 

By far the best general exhibitions of the material are in the neigh- 
borhood of Pyramid Lake and the valley of the Truckee. Here the steeper 
slopes of Lake Range and of the northern projection of Virginia Range, 
where they flank the lake, are thickly coated with pure gray thinolite, 
which at the uppermost levels carries a considerable amount of angular and 
sometimes rounded fragments, imbedded as in a conglomerate. 

Decidedly the most interesting single specimens of thinolite outcrops: 
are to be seen at the Domes, the Pyramid, and Anahé Island. The Domes 
particularly are of extreme interest. They are a series of bold spheroidal 
forms, partly bordering on the east shore of Pyramid Lake opposite the 
Pyramid, and partly rising as detached, abrupt islands above the surface 
of the water. They are immense botryoidal masses, always showing more 
or less of an obscure central opening, as if they were due to spring currents 
and had been built up like some of the domed mounds of thermal springs. 
The Domes themselves are from fifty to sixty feet in height, the caleareous 
material generally of a light-brown and light-gray color. The Pyramid, 
a remarkable detached island from which the lake takes its name, rises 
about a mile from the shore, having an extremely narrow base and an alti- 
tude of about 400 feet. Plate XXIII. shows the thinolite domes and the 
Pyramid. Almost its entire surface is incrusted with relics of a thinolite 
coating, which at one time must have covered it uniformly. 

About three miles from the eastern shore is the bold Anahé island, 
which reaches 500 feet above the surface. Terrace lines having been 
observed fully 500 feet above the present water's edge, no doubt this island 
was formerly entirely covered by the waters of Lake Lahontan. The island 
is about a mile across, and fully three quarters of its surface are thickly 
covered with thinolite, or show traces of its former presence where modern 
erosion may have remoyed it. The incrustations on the steep upper slopes 
of the island around the central peak are extremely peculiar. They possess 
a rough botryoidal surface, which has the appearance of being made up of 


huge mushroom-like forms that overlap each other like roof tiles. When 


516 SYSTEMATIC GEOLOGY. 


closely studied, each special mushroom-like member is seen to have an 
independent central stem. Plate XXIV. gives a near view of a portion of 
this singular thinolite surface. The coating is from ten to twenty feet in 
thickness, and the surface is one of the roughest imaginable geological 
exhibitions. It is only equalled by the frothy and porous surface of a 
newly congealed lava-flow. 

The lower valley of Truckee River is cut through a cation of hori- 
zontal sands, assumed from their connection with the Humboldt beds to be 
of Pliocene age. This canon, in continuing northward toward the lake, 
cuts deeper into the formation, and at last the abrupt banks are over 200 
feet in height. Upon the plateau-like summit of the beds, on the edges of 
both the east and west walls of the cation, thinolite appears in very curious 
forms. Itoccupies the surface of the Pliocene beds in broad mushroom-like 
bodies, varying from two to eight feet in diameter, having smooth, round 
surfaces entirely free from the coral-like openness of structure observed in 
the great banks where they are incrustations on the inclined rocky surface. 
The peculiarity of these mushroom-like formations is, that they are 
gathered together, forming a complete surface of country, touching edge 
by edge, and that from the middle of these round bodies there is a distinct 
stem which penetrates the Pliocene sands to a depth of from one to 
three feet. Besides these, the Pliocene itself is more or less coated with 
irregular flat sheets of thinolite. The effect upon the edge of the 
canon wall or upon the edges of the side ravine, where erosion has cut 
away the supports of the mushrooms and left them overhanging on the 
brink of the walls, is peculiar in the extreme. Certain limited passages 
of the Pliocene surface carry these mushrooms, extremely smail, about 
the ordinary dimensions of the edible fungus. Specimens, with a cen- 
tral stem, and the whole root phenomena, were submitted to a com- 
petent botanist, who at once saw in them petrifactions of fungoid growths ; 
but they are without doubt of a concretionary or crystallitic origin. 
The lower figure of Plate XXV. gives an idea of these mushroom forms 
on the edge of a canon, Pliocene strata showing below. It is evident that 
the thinolite tufa formed after a considerable bevelling of the Pliocene, 
but before the final cutting of the present Truckee Canon, since the thino- 


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QUATERNARY. 5 Lf 


lite nowhere covers the sides of the cafion, but comes in an even sheet up 
to the very edge of the walls on both sides. 

The immediate surface of the rough thinolite coatings on the rocks 
at Pyramid Lake is very well shown in the upper left-hand detail figure of 
Plate XXV. The curious, rude, botryoidal surface, with its markings and 
pits, is seen, and a little within the botryoidal zone may be detected the 
irregular, imperfect forms of crystals. The left-hand middle figure of the 
detail plate shows a region of the underlying irregular crystals just under- 
neath the superficial botryoidal zone. This is composed of an intricate 
net-work of imperfect octahedrons, varying from an inch to one sixteenth 
of an inch on the shorter axis, but elongated up to a foot in length. The 
right-hand upper figure of Plate XXV. gives a better view of these irregular, 
distorted, long octahedrons, and shows also their manner of interference, 
and the peculiar branchlets which grow out at angles from the sides of the 
main crystals. 

A large number of thin sections from the solid beds of thinolite, from 
mushrooms of the Truckee valley, from the smooth surface of the Domes, 
and from a variety of solid thinolite material collected over the Carson and 
Humboldt desert, when examined under the microscope show distinct 
translucent crystalline forms, surrounded by a dull opaque gray substance, 
which, as the sixteenth objective shows, derives its gray color from a cloud 
of minute foreign particles. The included distinct erystals vary in size 
from very minute forms to half an inch in diameter, and show numerous 
angles which, when measured, show close approximation to the angles of 
gay lussite. 

I submitted several of the more perfect crystalline forms to Prof. J. 
D. Dana and Mr. E. 8. Dana. After a very careful examination they con- 
firmed my reference of the mineral form to gaylussite. Unable to obtain 
specimens of the “clavos” from Lagunilla, in Maracaibo, I have not been 
able to compare the elongated nail-form of the octahedrons of that locality 
with similar bodies here; but the Lahontan forms of the thinolite crystals 
are unquestionably a peculiar development of the mineral gaylussite. Over 
a very large part of the thinolite area these imperfect crystals are abun- 
dant. This is true of all the porous developments of tufa. On the other 


518 SYSTEMATIC GEOLOGY. 


hand, wherever it is smooth and consolidated, thin sections show the inclu- 
sion of a large number of minute octahedral crystals having the long nail- 
shape, with others more related to the shorter shapes of the larger Soda 
Lake. A full examination of a large number of field localities and collected 
specimens leads me to the belief that the entire thinolite formation, with 
all its enormous development, its extent of hundreds of miles, its thickness 
of 20 to 150 feet, was nothing less than a gigantic deposit of gaylussite 
crystals. 

Referring now to the table of analyses of desiccation-products of Lake 
Lahontan, it will be seen that there are three analyses given of the thino- 
lite—one from the tufa dome on the shore of Pyramid Lake, one from a reef 
in Carson desert, twelve miles north of Ragtown, and one from the basaltic 
slopes of Truckee Range just above the mushroom-capped Pliocene strata, 
where their surfaces of thinolite abut against the foot-hills east of the cation. 

The included silica, which is chiefly mechanically entangled sands, 
and not an integral part of the crystalline thinolite, varies from 2.19 per 
cent. to 7.27 per cent., and the alumina varies correspondingly from 8 per 
cent. to 24 per cent. The included foreign material is, therefore, siliceous 
and feldspathic sands. The percentage of magnesia rises in one instance, 
at the Carson desert, to 4 per cent.; there is always a little soda, a little 
potash, traces of phosphoric acid, about 1 per cent. of water, and about 
90 per cent. of carbonate of lime. The thinolite is, therefore, practically, 
and leaving out of consideration the mechanical impurities, a pseudomorph 
of carbonate of lime, after gaylussite. 

The chemical deductions from this interesting fact are of exceeding 
importance in the history of Lake Lahontan. In the study of the alkaline 
desert lakes near Ragtown, we have seen that at the stage of the greatest 
fullness of water or greatest weakness of solution the gaylussite crystals are 
redissolved and none are to be seen. On the other hand, at the close of the 
long evaporating-period of the summer, the waters having very materially 
diminished and the solution become dense up to the point of erystalliza- 
tion, gaylussite freely separated out. 

A spirit-level determination of the highest observed thinolite places 
it at 470 feet above the 1867 level of Pyramid Lake, whereas the highest 


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QUATERNARY. 519 


observed terrace-lines are about 500 feet above the 1867 level of the lake. 
There were therefore about thirty feet between the highest level of the lake 
and the highest point at which thinolite formed. From its highest develop- 
ment there were nearly continuous sheets incrusting the mountain slopes 
upon both sides of Pyramid Lake down to the water level, and, at the time 
of the examination in 1867, sailing over the very clear water in the neigh- 
borhood of the Pyramid, Anahé Island, and the Domes, and also when 
standing at the top of the Domes and on the Pyramid, it was seen that the 
thinolite formation extended far beneath the level of the water. It is 
probable that we saw at least thirty feet of thinolite surface below the 
water level. 

The present solution of Pyramid and Winnemucca lakes is so low in 
saline contents that the mineral gaylussite, which was the original basis 
of the thinolite, could not by any possibility be formed. Moreover, the 
present waters are so weak in alkalies that carbonate of lime is still held 
in solution. It is therefore evident that, at the time of this enormous crys- 
tallization of gaylussite, the great body of Lake Lahontan, filling up the 
area of four degrees of latitude in length by three degrees in breadth, with 
an average depth of 400 or 500 feet, must have been of sufficiently strong 
carbonated solution for the production of the mineral gaylussite. 

The experiments on the solubility of this mineral by Professor Allen, 
already mentioned, and the existing facts of its natural production by the 
concentration of the carbonated waters of the Ragtown Soda Lake, show 
that a dense solution of carbonate is essential to the formation of gaylussite. 
The thinolite itself, a pseudomorph of carbonate of lime after gaylussite, 
shows at once that the original mineral was formed in the highly car- 
bonated alkaline solution; the pseudomorph being a subsequent result of 
the addition of calcareous matter to the solution, the lime replacing the car- 
bonate of soda of the gaylussite, and transforming it into carbonate of lime. 

Whether we consider the solution after the formation of gaylussite, or 
still later after the liberation of carbonate of soda from the gaylussite during 
the act of pseudomorphism, it is evident that the whole Lahontan basin, up 
to the level of the highest thinolite, must still have been a concentrated car- 
bonate solution. When we now realize that the lake has dried away, and 


520 SYSTEMATIC GEOLOGY. 


whatever alkaline tenure it had at the period of desiccation must have been 
gradually concentrated in the lower residual basins—namely, the present 
and when we further consider 


existing lakes within the Lahontan area 
that the present lakes are so fresh as to permit the healthy life of numerous 
fishes, including one or two of the Salmonida, it is evident that the present 
waters do not represent the residual concentration of the great carbo- 
nate lake 

To account for the enormous accumulation of saline matter in the orig- 
inal Lake Lahontan to a sufficient density for the development of gaylussite, 
it is of course obviously necessary that the lake should have had no outlet; 
in other words, its waters were constantly concentrating by evaporation, 
never flooded out by any considerable overflow. The occurrence of such 
a tremendous formation of alkaline carbonates, to say nothing of the other 
contents of the lake, necessitates a very long period during which the 
surface of Lake Lahontan was some distance below its level of outlet. To 
account for the existing presence of the weak solutions of the residual lakes, 
it is necessary, after the formation of gaylussite and its pseudomorphism into 
thinolite, to suppose a flood-period during which the lake had free drainage 
over its outlet, and which continued long enough to wash out practically 
the whole saline contents of the great lake. 

The chemical nature of thinolite, therefore, necessitates, first, a long 
continued period without drainage to the sea, during which the inflowing 
waters, derived both from the direct drainage of the tributary rivers and 
from the carbonate-producing springs of the basin, were enormously 
concentrated by continued evaporation; secondly, the solution having 
arrived at the required density, a general development of gaylussite erys- 
tals incrusting the walls and slopes of Lake Lahontan. Supposing the 
solution concentrated to the point of the formation of gaylussite, we have 
no direct means of saying whether the mineral would form over the whole 
sides and bottom of the basin, or whether it would simply form on the 
shores as the waters concentrated and the lake shrank by evaporation. The 
analogy of Ragtown Soda Lake would seem to indicate that gaylussite forms 
only near the surface, and the arrangement of the tufas over considerable 
terraces would further seem to warrant the belief that it was a shore product 


QUATERNARY. 521 


marking the gradually retiring water-line. It is, however, chemically 
quite possible that with a solution of moderately uniform density and of 
sufficient concentration for the development of crystals, they might form 
simultaneously over the bottom and sides ; but that seems the less probable 
hypothesis. A further argument in favor of the thinolite having formed as 
a shore deposit, is to be found in the occurrence of angular and rounded 
beach gravels in it at numerous points, although generally the thinolite 
found upon the immediate bottom of the lake is rather free from included 
fragments. This, however, would naturally be the case from the remote- 
ness of these lake-bottom thinolite bodies from any shore line where pebbles 
could have been washed in among the forming crystals of gaylussite. 

If the desiccation was carried down, say to the present amount of 
water within the Lahontan area, the entire surface of the extreme low 
levels must have been covered by an enormous saline residuum composed 
of the excess of soluble salts over the amount required for the gaylussite. 
The present condition of the basin and the freshness of the lakes show that 
after this period of desiccation came a second flood-period, which raised the 
level of the lake to its height of overflow and washed out all the soluble 
salines of the basin. In this process of refilling the lake and diluting the 
solution, it is evident that there would still be carbonate enough to preserve 
the gaylussite, because gaylussite had continued to form down to the lowest 
levels. In the second flood-period which removed the great saline contents, 
during the process of filling the lake, there must have been either a cessa- 
tion of the addition of carbonates by springs, or an excess of lime brought 
in by the rivers. At all events, the process of pseudomorphism occurred 
before the solution was weak enough to redissolve the gaylussite crystals. 

When we realize that during the formation of gaylussite as seen in 
Ragtown Soda Lake there must always be a great excess of carbonate, 
and all the lime is made into gaylussite, it must be admitted that in the age 
of pseudomorphism there must have been density of solution sufficient to 
retain the crystals, and yet lime enough to furnish the material for the 
pseudomorph. It is rather a delicate chemical question, how the solu- 
tion ever should have contained lime enough for the pseudomorph, and 


yet carbonate of soda enough to prevent the re-solution of the gaylus- 


522 SYSTEMATIC GEOLOGY. 


site. In a single alkaline deposit, that of the upper Humboldt Valley, 
there is a considerable amount, reaching in one instance 12 per cent., of 
chloride of calcium. Suppose after the formation of gaylussite, the lime, 
instead of coming in as carbonate by the slow delivery of the rivers, was 
a hot-spring product in the form of chloride. The chloride of calcium 
coming into the presence of an excess of carbonate of soda, double decom- 
position would occur, making carbonate of lime and chloride of sodium, 
providing the solution were of the requisite density. It would seem that a 
process of that kind might account for the substitution of carbonate of lime 
for the carbonate of soda of the gaylussite. However that may be, a 
second flood-period evidently washed the entire basin free from all soluble 
saline contents, and maintained it for some time as a pure fresh-water lake. 

The subsequent desiccation of that lake, starting with a pure, fresh 
water, and carried down to the present almost complete drying-out of the 
basin, is the last fact in the history of this lake of which we have any knowl- 
edge. Weare therefore warranted in assuming, first, a lake having an outlet ; 
secondly, the sinking of the level of that lake by evaporation below the 
level of outlet; thirdly, the long continued concentration by evaporation of 
its saline solution up to the point of the formation of gaylussite; fourthly, 
the desiccation of this lake and development of the great incrustations of 
gaylussite crystals, and possibly, though not probably, the formation of the 
pseudomorph; fifthly, the coming on of a second flood-period which filled the 
basin to its point of overflow ; sixthly, the maintenance of the lake at its 
maximum level long enough to wash out the soluble salts completely, and 
probably, during this period, the formation of the pseudomorph; seventhly, 
the modern rapid desiccation from the point of maximum fullness down to 
the present, in which only the few lowest basins contain the meagre residual 
weakly saline lakes. 

When we come now to correlate the features of this chemical history 
with those brought out by the relation of the sediments of Lake Bonne- 
ville, as clearly shown by the observations of Gilbert* and myself, we find 
that the reading of the sedimentary deposits shows, first, a period in which 
the lake basins were dry, and during which subaerial gravels washed down 


*United States Geographical Surveys West of the One Hundredth Meridian, Vol. II., Geology, 
Chap. III. 


QUATERNARY. 523 


the slopes far into the heart of the lake basin; secondly, a flood-period in 
which the lacustrine sediments accumulated over the whole floor of the 
lake, overlying the lower extension of the earlier subaerial gravels; and, 
thirdly, the present period of desiccation, in which the waters of the lake 
have dried out and a second subaerial gravel formation has been washed 
down its slopes, covering the edges of the lacustrine sedimentary beds. 

Gilbert, therefore, beginning at the present, shows our period of dryness 
to be immediately preceded by a period of high humidity, in which Lake 
Bonneville was filled to the brim, and a period of dryness anterior to the 
Bonneville Lake. The chemical history of Lake Lahontan, when corre- 
lated with this, shows not only those three periods, but a period of humidity 
anterior to Gilbert’s earliest age of dryness. For the clear reading of the 
chemistry of Lahontan is: our modern period of desiccation corresponding 
to the period of latest subaerial gravels, as displayed both in the basin 
of Lahontan and of Bonneville; a period of flood immediately preceding 
that, during which the saline contents of Lahontan were washed out, and 
during which Bonneville was filled to its highest terrace; Gilbert's earliest 
period of dryness, which corresponds to the age of the thinolite desiccation 
of Lake Lahontan. The appearance of thinolite itself up nearly to the 
highest terraces of Lahontan shows a period of moisture anterior to Gilbert’s 
first period of desiccation. 

Gilbert justly remarks that the Bonneville beds appear as an episode 
occurring between two periods of aridity. The addition of a still earlier 
period of humidity to this series of climatic changes could never have been 
arrived at from the lake sediments alone, since the lacustrine beds of the 
second humidity-period would naturally cover up and obscure those of the 
first humidity-period. 

Could we obtain a section deep enough on the borders of the two 
lakes, beneath the earliest subaerial gravels which Gilbert and I have ob- 
served in both basins, there would doubtless be seen still earlier lacustrine 
beds underlying the bottom of the thinolite. 

That Lake Lahontan was filled before the formation of the first gay- 
lussite, is proved by the position of the pseudomorph of that mineral nearly 


up to the point of outflow. The earliest knowledge, then, we have of these 


524 SYSTEMATIC GEOLOGY. 


lakes is of their being full. When we compare the amount of salinity which 
was retained within the lake basin in the first period with that which is now 
observed as the result of the second desiccation-period, it is at once seen that 
the first lake had an enormous excess of soluble salts over the second lake, 
since its chemical residua on evaporation contained such a vast amount 
of carbonate. Making all due allowance for any change in the chemistry of 
the springs of the basin, which at that time must have yielded an immense 
amount of the alkaline carbonates, and which now yield very little of the 
same salts, it will be seen at once that the period of concentration of the 
first lake, namely, the period at which it was maintained at a high level, 
though below the point of outlet, must have been enormously longer than 
in the second age of desiccation, since the residual products of the second 
period of desiccation are not enough to render even the small existing lakes 
very saline. We are therefore warranted in assuming for the first age of 
humidity of the lake an enormously long continuance as compared with 
the second. The first long-continued period of humidity is probably to 
be directly correlated with the earliest and greatest Glacier period, and the 
second period of humidity with the later Reindeer Glacier period. 

The Quaternary lakes of the Great Basin are therefore of extreme 
importance in showing one thing—that the two glacial ages, whatever may 
have been their temperature-conditions, were in themselves each distinctly 
an age of moisture and that the interglacial period was one of intense dry- 
ness, equal in its aridity to the present epoch. 

It is worth while to emphasize the fact that the present is essentially a 
period of desiccation, as contrasted with the wet periods during which the 
Quaternary lakes were filled. The Glacial periods, then, must have been 
far more moist than the climate of to-day. As regards the heat-condition, 
I have before called attention to the fact that the mean annual temperature 
over a considerable part of the United States Cordilleras is to-day lower 
than over the still glaciated portion; that the difference between the gla- 
ciated and the still colder regions is simply one of relative moisture. 

Suppose a secular change to occur now, in which the climate of the 
northern hemisphere should for a time become colder than at present. It 
is obvious that there would be less evaporation of the oceanic moisture, and 


QUATERNARY. 525 


that the winds which carry that moisture over continental areas would be 
even drier than at present. Even with the relative humidity which now char- 
acterizes these winds during a lowering of the temperature, it is extremely 
doubtful whether glaciers would form. In the presence of greater cold 
there would be a greater precipitation relative to the moisture of the conti- 
nental atmosphere; but that atmosphere itself would be correspondingly 
drier from the diminished supply evaporated from the ocean surface. On 
the contrary, in a warmer period, the sea-winds blowing over the continent 
would bring a greater amount of moisture, and there would be, as regards 
the whole area, a correspondingly greater precipitation; and the cold, 
high-altitude points or climatic islands of low temperature would still act as 
powerful condensers and extract from the moister winds more snow than at 
present. The instructive example of New Zealand affords an illustration of 
the abundant production of glaciers in a climate of higher mean tempera- 
ture and greater relative humidity than that of the United States. 


Late writers on the Great Basin, especially G. K. Gilbert, have called 
attention to the rise and expansion of Salt Lake. I have already shown 
that between the period of the Stansbury survey and that of my own there 
was an increment of 600 square miles in the area of the lake, and a rise of 
eleven feet. In popular discussions, it has frequently been suggested that 
the additional cultivation of the desert lands by the system of artificial irri- 
gation introduced by the Mormons had brought about the change. 

This hypothesis is too absurd to require detailed refutation. The 
cycle of moisture which has recorded itself in the increased volume of 
Salt Lake is also evident in many other localities and in different ways. 
Mono and Owen’s lakes at the east base of the Sierras show a correspond- 
ing rise, and, as has been stated before, all the residual lakes in the basin 
of Lake Lahontan evince the same change. When it is remembered that 
the moisture-bearing wind, indeed the entire source of aerial moisture for 
the whole western Cordilleras, is the upper, constantly blowing west-to- 
east wind, it will be seen that no changes of cultivation of unimportant, 
isolated agricultural regions could possibly have brought about the 
general increase of humidity. This increase of the volume of the lakes 


526 SYSTEMATIC GEOLOGY. 


has taken place in the presence of an enormous power of evaporation. 
Over a very large part of the Great Basin the average climate is so dry 
that there is a wide permanent difference between the observations of wet 
and dry bulb thermometers. During the period of maximum evaporation 
in midsummer and even in November I have recorded differences of 36°. 
Observations were made by my party with a series of evaporating-pans, 
which were observed in the shade and in the sun, and by means of a delicate 
micrometer screw actual hourly and daily evaporations were noted. A half 
inch a day was not an uncommon result in the dryest period of the year. 
It becomes a question of great interest to determine whether this 
recently observed climatic oscillation is within the range of frequent occur- 
rence, or whether it is a noteworthy departure from the climatic habit of 
the immediate past. Some light is thrown on this question in the alpine 
regions of the Sierra Nevada and the higher points of the desert ranges. 
The phenomena, however, are so much more clearly shown upon the Sierra 
summit, that I confine myself to that region in discussing this point. 
Below the line of perpetual snow is a variable, open region of about 
1,000 feet in altitude, in which the tree-growth is rather sparse and com- 
prises only strictly alpine species. Below that point, from Alaska nearly to 
the Mexican line, is a continuous dense growth of coniferous forest. A very 
large number of observations on the average age of the timber growth at its 
upper limits shows a mean of about 250 years. Since the late cycle of 
increased moisture, the winter accumulation of snow on the Sierra summit 
is evidently greater than since the earliest growth of the present forest. 
The barren zone which I have mentioned, between the perpetual snow 
and the main timber growth, represents a region where the snows accumu- 
late too thickly for the propagation of the coniferous species, and may be said 
to express the downward limit of the encroachment of snow for 250 years. 
In the present climatic change the snow accumulation is greater, and 
extensive avalanches where the topographical configuration favors, have 
begun to pour down into the true forest belt and to sweep before their rush 
considerable areas of mature tree growth An avalanche starting in a 
high alpine gorge ploughs its way downward, not infrequently mowing 
down a half mile of adult trees. It is obvious that no such avalanches 


QUATERNARY. SPAT 


could possibly have occurred during the germination and growth of this 
forest. 

On the summit of the Central Pacific Railroad Pass are a considerable 
number of well grown coniferous trees. An examination of them during 
the construction of the Pacific Railroad showed that they were at that 
time being seriously damaged, and in some cases actually killed, by the 
drifting snow-crystals borne on the strong west winds during the winter 
storms, the notch or depression of the pass making a sort of funnel, through 
which the wind blew with unusual violence, concentrating its freight of sharp 
snow-crystals, which not only wore away some of the foliage of the trees, 
but actually cut off the bark from exposed positions and sawed into the 
wood for several inches. An inspection of the branches thus cut showed 
that the annual rings had formerly perfected themselves, and that the snow 
had worn off a considerable portion, often several inches, of the thickness 
of the wood, leaving a smooth polished surface, displaying the cut edges of 
the layers of annual growth. From these facts it would appear that the 
existing climatic oscillation began before the year 1870, and was the first 
of its kind for over 250 years. The year 1866 is about the date of the 
increase of Salt Lake. Mono Lake shows a rise in 1864, and the destruc- 
tive Sierra avalanches began about 1860. Although unimportant in its 
general results, this oscillation becomes a matter of very great interest 
from a theoretical point of view. 


The mechanical and chemical facts which have been observed in the 
Quaternary phenomena of the Fortieth Parallel show that post-Pliocene 
time has been marked by a very long period of very great humidity, fol- 
lowed by a period of intense dryness, which gave way to a second but 
briefer epoch of humidity, which was rapidly succeeded by the present age 
of drought. In comparing these climatic phenomena with what we can tell of 
the Pliocene, the Quaternary appears to have been a much more varied age. 
In the deposits of the Pliocene there are certain alkaline beds which I have 
noted, and which seem to me to mark periods of desiccation; but in all the 
mountain phenomena and in the sediments there are no appearances which 
could suggest the presence of a considerable glaciation. 


528 SYSTEMATIC GEOLOGY. 


We know from the fauna and flora of the Pliocene that it was a warm 
age, permitting palms and crocodiles to extend as far north as the British 
line. The interior of the continent had at least two enormous fresh-water 
lakes, one covering the area between the meridian of the Wahsatch and 
that of the Sierra Nevada, the other the province of the Great Plains. To 
maiutain these great interior lakes it must therefore have been an age of 
very great humidity. 

During the Quaternary age most modern mountain topography received 
its present form. Most, if not all, of the sharp cafions were carved, 
and the mechanical results of that erosion are seen in the great accu- 
mulations of subaerial gravel in regions of interior drainage like the Great 
Basin, and in deposits of unknown thickness classed as Lower Quaternary, 
which gathered on the beds of the Quaternary lakes. The long carbonate- 
lake period which followed the first great flood-age of the Quaternary was an 
age of desiccation even greater than the present, as is proved by the occur- 
rence of thinolite on the deep bed of Pyramid Lake. In other words, the 
lakes of that period were practically completely dried. 

During the long continuance of that earlier drought a very large amount 
of the Fortieth Parallel area must have been even more devoid of desert vege- 
tation than at present, and the dry west wind must then have drifted an enor- 
mous amount of fine sands from west to east. Even now this process is 
seen in operation at various points in the Cordilleras, where trains of dunes 
are gradually moving eastward. This is especially observable in the region 
of the Colorado desert in southern California, where the prevalent west wind 
sweeps the desert floors clean of their fine loose material and banks zolian 
sands high up on the west faces of the mountain ranges. If Richthofen’s 
theory of the olian origin of Loess be finally accepted, the dust deposit 
which is now the Loess of the Mississippi Basin might readily, as Pum- 
pelly has shown, have blown from the desiccated regions of the western 
Cordilleras during the great drought which immediately followed the first 
great flood or glacial period. 

Contemporaneous geological action on the area of the Fortieth Par- 
allel is confined to the slow and extremely limited transportation of mate- 
rial by the rivers, the feeble xolian transportation, the slow accumulation 


| ; 
Nab KeSCarsi a H Total. 
| = 
1.63, 1.97 0.73 100.00 
98.12 
| fall. 82| 8.57 . + | 100.00 
SOs | 
n30)5} || 0.24 99-06 
| 
+ free CO? | 
0-99 2-81} 28.93 + « | 100.00 
Na 
| 0.04 99-87 
| Na 
/0-13 99-96 
| | 100.00 
100.00 
eh é 
S|CaCjMgC|Mg ¢ ) & | B | ‘otal. 
£281) .o157 3-2365 
| 


TABLE OF CHEMICAL ANALYSES, V.-UNITED STATES GEOLOGICAL EXPLORATION OF 
DESICCATION-PRODUCTS OF LAKE LAHONTAN. 


Efflorescences and Lake Salts. 


THE FORTIETH PARALLEL. 


NaCl |NaG|Na C+C 


s a8 : ae oe 
S| eae i eee 2 | os 
25 Locality. Analyst. Bs Fe|/ Ca | Ca|Mg|Mg| Na] Na | KR | Lil] cl © | Sy By Py sey ae < Be Total 
z* me ee) | eee cee Ji ehe |e. | 
45 | Maag’s Station, Truckee Desert -|O.D. Allen - - / | 95-67 
wad i | : | 
46 } Hardin City- = = - - = - - ws | . || . (eat es eee oa Go }ho9 of |erallis | ao! j - | 18.47 
| | i H | | 
47 | Sink of Quinn’s River- - - - - Ws | | H 85.27 
48 | Buffalo Station - - - - - - - cD per ikealfeie ||sacis | 36:25) mifor87| tr. 42.97) . - 3 6 Gade | tie, 70.81 
49 | Gay-Lussite, Soda Lake, Ragtown iS ~ =} =| tg-r9}- -}- -|- =| 79:95] = |. aI). .| tr. 29-55| tr 31-05 | 0.20 99-94 
| | 
50 | Trona, Soda Lake, Ragtown - - © a 1b | 3 oll So ullu alto 4ilo= oll MGH7GI 0 0.46 37-88) 0.35 20.07 | 0.30 99-83 
51 | Salt from Soda Lake, Ragtown - - c agra Wee ieee econ tees . | 40-53 eee |- - | 0:98 36-74] 0-75 | tr. | tr |- -| 19.93] 0.80] 0.22 g9-5r] - 
40-57 | 0.97 36-87) o71 | tr. | tr 19-87 | 0.80 | 0.22 99:57] - 
52 | Salt from small Soda Lake, Ragtown se me 6 cd eoedle ala. (|s cet ee. tre doe Kee od Pe Raa ine, |) ile, ‘ | I-10 
} | 
53 | Deposit from Soda Lake, Ragtown | R.W. Woodward | 78.50. .| . .|. . | 2 |e isieg4| oom |. - | 0-20) 10-39) |) 46) Norge eaeo 99:87 0-43 
| i | } 1 
FESS o allo ollo o | Bolla of yegis| Cogn || > qamiemeel| Certs) | Mets | efOon§|) eum) |ic a |lo | Sp | 99:96 | 0-47 
| 
54 | Brown’s Station, Humboldt Lake - ff KeBeeS ol) 5 oije allo allo ollattelinopccl) tn, || o Aelia eters 2.48 6.50 11.76 | 6.78) . E S 100.00 49-67 
5 : BUEN }0- 0-0. olla 0 | + f+ =| 22.88) ro.5n) tr} .|. - | 30-02 2.48 6.50 11.73 | 6.78) . z + 100.00 49-63 
| | | | 
55 | Salt, incrusting decomposed Rhyo- rs 4-50/- .| Chiefly Na Cl on surface of specimen). . |: 2 1 
lite, Red Hills, West Humboldt. | 
Ser 2 mee - poses Z pee sol I A be NR Ue 
Phimolite (Pseudo-Gay-Lussite). 
eae mee —— — # Pee Sea ee Z 
°c 
sd | Analyst & | Ai | we | Ca | Mg | Na ee) | ataent, | Soe 
ae Woes ies a i g “|| gravity. 
22] } 
4 renee 2 a ee | faces at ele Be ie a IY 
| 7 ad | i) Po® a 2 
56 | Tufa Dome, Pyramid Lake - - - | R. W. Woodward} 7.27*| 2.14 | tr. |) so3 try) 200s 8-23 90H 8 2-4 
POs 
| | Ggo*} 2-54 || tr. | AGS \ {is ote) | 6 52) 99:81 
A . RO# | . 
57 | Twelve miles north of Ragtown, BAR| OH { so ft | ++ 44-35 | 100.01 |2-5, 2.5, 2-5 
| Carson Desert. Pos 
2.19* | 0.82 | { SO3 \ tr. 41-43 | 100.30 oe 6 
my | BO® j GEG 
58 | Near Wadsworth = - - - - - a 3:01* | 0.89 Shvisos iis Hote pee [oo 2.46, 2.41 z 
i Pos aH | 
| 3-10* | 0.86 : | Ree \ tr. 1.40 oe nO || 5 
| z = 
= =: CaaS silicic acid rl cram, 
Waters. 
} | a 
| | 
Ae Locality. Analyst. Si | Ca | Mg | Na Ce Stienel 5 
2 z | i eh : | Free. Le 
| EMER -02392 
59 | Pyramid Wake. = == 25S =» =O: yAlicneeeees erin ee +1292) 4234] -8999) t D: 2) und, || 1.3870}. 
5 UN yo Sees | Smo ip co ee |e I 
60 | Sodaakes ey) “a +2050) - /.0230| . - |42.838 ; tr. eee” 39-394) 0978 +430. 
; : 
— + 2 . . u . Al ny P 
Gr } Humboldt Lake - - --- - - , yr : sige +0274) to70 | 2952 0. 


| 
| 52-10) 
26.08 
| | 
66.27 
| 
dj 98-49 0-91 
98-51 0.85 } 
18.15 | 20.88 | 
18.15 | 20.84} 
| 
| 


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STALL 1 13 IRC WO) 1D) 


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LR U0 FALL ny 


QUATERNARY. 529 


of calcareous precipitates and river sediment in the beds of the present 
shrunken lakes, the disintegration of mountain tops and formation of 
angular, high-mountain débris, and the few rare instances of true oro- 
graphical action, in which the solid rock foundations of the country are 
absolutely faulted, the most conspicuous example of the latter being the 
great fault described by Prof. J. D. Whitney* in his account of the Owen’s 
Valley earthquake of 1872. 


* Overland Monthly for August and September, 1872. 


34K 


ae Te a Sen ra a : 


CHAPTER VI. 
RESUME OF STRATIGRAPHICAL GEOLOGY. 


It is the purpose of this chapter to present in the briefest possible 
manner the leading outlines of stratigraphical geology in the area of the 
Fortieth Parallel. In the foregoing chapters I have given the reader 
a summary of such facts as seemed to be necessary to a general compre- 
hension of the sequences and subdivisions of the sedimentary geology. 
It seems appropriate that the enormous developments of strata which have 
there been described should be succinctly shown in their broader geograph- 
ical and historic relations. 

In the 120,000 feet of sedimentary accumulations the grander divis- 
ions of Archean or Azoic, Paleozoic, Mesozoic, and Cenozoic are dis- 
tinctly outlined by divisional periods of marked unconformity. Considered 
as a whole, there is a noteworthy fullness in the geological column. None 
of the important stratigraphical time-divisions are wanting except those 
obscure intermediate deposits which in other countries lie between the 
base of the Cambrian and the summit of the crystalline Archean series. 
From the first of Cambrian age to the present every important interval 
of time is recorded in the abundant gathering of sediments, which are 
with singular fullness characterized by appropriate and typical life-forms 

As in all other geological fields, the most important interruption of 
the continuity of deposit was at the close of the Archzean age, and the 
most striking difference between any two successive groups of rocks is that 


which characterizes the relations of the Archean and the Paleozoic. With 
581 


5 


5 


2 SYSTEMATIC GEOLOGY. 


the exception of a few slates of supposed Huronian age, which the micro- 
scope shows to be richly charged with crystallites, all the non-eruptive 
Archean rocks have passed from the original condition of detrital beds into 
sheets or bodies of distinctly crystallized material. 

Not only are the Archzan exposures of such frequency over the For- 
tieth Parallel area as to insure a moderately complete knowledge of strati- 
graphical sequence and materials of the period, but also, owing to the rela- 
tions which have been described with the overlying Paleozoic, I am able 
to reconstruct with considerable accuracy the topographical configuration 
of the Archzean surface. Supposing all the post-Archzan rocks to be 
removed, and considering what we now know of the whole area at the close 
of the Archean age, the first prominent fact is, that coextensive with the 
greater part of the Cordilleras—that is, from longitude 104° westward as far 
as the Archean exposures extend—was a great Archean mountain system 
built up of at least two sets of nonconformable strata, referred to Lauren- 
tian and Huronian; the lower and older composed of granitoid gneisses 
chiefly made up of quartz and orthoclase, but carrying a little mica, sparing 
triclinic feldspars, and chlorite pseudomorphous after garnet and mica. 

Over these, whether with actual conformity or not is undetermined, 
lies an enormous series of mica gneisses rich in quartz and biotite, orthoclase 
ordinarily exceeding plagioclase. The earlier aplitic gneisses and the later 
mica gneisses expose about 25,000 feet each of conformable beds. 

A third group, nonconformable with the earliest aplitic series, the rela- 
tions with the intermediate mica-gneiss series being unknown, consists of 
mica and hornblende schists passing upward into slates, quartzites, lime- 
stones, and dolomites. 

In the mica schists biotite predominates, and is usually associated with 
an excess of orthoclase over plagioclase. When muscovite replaces biotite 
it is frequently accompanied by garnet. The hornblendic schists are gen- 
erally characterized by the presence of zircon, and, as a rule, carry 
plagioclase in excess of orthoclase. Interstratified with the quartzites 
are beds of smooth, rounded conglomerates, sheets of dioritic (horn- 
blende-plagioclase) schists, and in one or two instances hydromica (para- 
gonite) rocks associated with kyanite and staurolitie schists. The lime- 


STRATIGRAPHICAL RESUME. 533 


stones, prominently dolomitic, are usually intercalated with mica gneisses, or 
overlie the oldest quartzites. The mica gneisses, which form the lowest part 
of the third group, so closely resemble the highest mica gneisses of the second 
group, that, although they are never exposed in conjunction, it is supposed 
that they are one and the same series, and that groups No. 2 and No. 
3 are conformable, making, therefore, but two conformable series, the 
lower granitoid beds and the upper composite group, as described. 

The geographical range of the lower series is confined to the country 
between the 104th meridian and the Wahsatch. The upper series appears 
to extend over nearly the whole Fortieth Parallel area. West of the 
Wahsatch the folded, crumpled, dislocated masses of these sedimentary 
Archean groups are invaded by plastic, structureless granites of four litho- 
logical types, for whose petrological characteristics the reader is referred to 
the second section of Chapter II. and to Volume VI. 

Upon grounds set forth in Section IV. of Chapter I. it is clear that the 
general topography prior to the deposition of the earliest Cambrian rocks was 
that of a great mountain system, displaying lofty ranges made of crumpled 
strata, enormous precipices, a result of mechanical dislocation, and, finally, a 
type of high mountain sculpture of such broad, smooth forms as to warrant 
the belief that subaerial erosion had never earved and furrowed the mountain 
flanks with the sharp ravines characteristic of modern mountain topography. 
East of the Rocky Mountains, in the geological province of the Great Plains, 
there are no Archzan outcrops; and when we consider the comparative 
thinness of the later sedimentary beds superposed over that region, the 
absence of outcropping Archean masses piercing through the later sedi- 
ments is excellent proof that over that area Archean mountain ranges did 
not exist. This is important as defining the Archean Cordilleras within 
the limits of the modern Cordilleras, or, as is a more strictly correct view, 
the ancient Archean Cordilleras have determined not only the general area 
but much of the local detailed structure cf the modern Cordilleras. 

The topographical features of the present terrestrial surface are far 
less grand than the Archean orography. The great Archwan precipices 
brought to light in Uinta and Wahsatch ranges are absolutely unpar- 
uleled in the topography of to-day. That prior to Cambrian time this 


534 SYSTEMATIC GEOLOGY. 


mountain system was a land area, is clear from the absence of interpolated 
sets of strata between the finished crystalline mountains and the uncon- 
formable Cambrian sediments. In the modern dislocations and disturb- 
ances which have enabled us to gain these profound views of the Archzean 
mountain systems, there is one interesting topographical element which we 
fail to reach. Never arriving at the bottom of the Cambrian sediments, we 
are at a loss to know the physical characteristics of the valley bottoms 
which lay between the Archzean ranges. Whether they contained relics 
of a land detritus, or whether they were washed smooth by the subaerial 
drainage of the period, we do not know. 

There is always a complete, sharp, unmistakable nonconformity between 
the crystalline Archzean topography and the superjacent sediments. 


Considered as a whole, the Paleeozoic series constituted a conformable 
body, laid down over the rugged Archean mountain system. It first ap- 
pears in the region of the Rocky Mountains with a total thickness of about 
a thousand feet, the strata surrounding and abutting against permanent 
Archzean islands, which, during the whole Paleozoic and Mesozoic, were 
lifted above the level of deposition. Throughout all Paleeozoic time only 
1,000 feet of strata accumulated over our part of the Rocky Mountains, 
and we get no glimpses of deeper hollows in which lower Cambrian beds 
might have been deposited. Passing westward, the series gradually thick- 
ens to 32,000 feet in the region of the Wahsatch and about 40,000 feet at 
the extreme western Paleozoic limit, longitude 117° 30’, where, from the 
evidences of shore-phenomena, and the non-continuation of the beds west- 
ward, we are warranted in assuming the Paleozoic coast. 

Superposed in unconformable succession over the gigantic crystalline 
mountain ranges, some of the tips of the highest peaks still rose above the 
level of the (inter se) strictly conformable Palzzoie series. At the close of 
the Paleozoic, the uppermost sheet of Carboniferous material, extending 
from the Nevada Palseozoic shore eastward through the whole Fortieth Par- 
allel area, was only interrupted by a few island-like granite peaks which were 
above the level of deposition ; the great mass of the Archzean topography by 
that time having been completely buried. Of the character of the Archean 


STRATIGRAPHICAL RESUME. 535 


land which still, at the close of the Palxozoic, formed the westward barrier 
to the ocean and the source the main detrital material, we know very little. 

The Carboniferous strata which are found west of the old shore-line 
in California and Oregon seem to me rather to indicate shallow bays and 
gulfs, which permitted the westward extension of the upper Paleozoic 
strata, while the great bulk of the series was stopped by a bold coast. 
Starting with a land area of Archean ranges, and passing on through the 
Paleozoic period until the whole Archean topography is buried in the 
deposits of a profound ocean, it is evident that the area has been one of 
very great subsidence. From its original altitude above sea-level it has 
been depressed to the ocean plane, and then downward until even the 
ocean-bed deposits have overwhelmed all but its highest peaks. 

Viewed regardless of the age of the individual beds, the Paleozoic 
series can be divided by the character of their materials into four great 
groups. The first is a purely detrital Cambrian, which, although of com- 
paratively fine sediments, in the presence of occasional conglomerates 
gives evidence of repeated subsidence. 

The second group is the great limestone series, beginning with the 
Pogonip Cambrian limestone, and extending upward to the top of the 
Lower Coal Measures for 11,000 feet, only interrupted, in the horizon of 
the lower Devonian, by a sheet, from 1,000 to 2,000 feet thick, of fine 
quartzitic detritus. 'This enormous group of 11,000 feet of limestone, char- 
acterized by abundant pelagic faune ranging from the Primordial to the 
top of the Lower Coal Measures, represents in general an age of deep seas. 
Toward the Nevada Paleozoic shore, however, in all the beds of the Lower 
Coal Measure limestones, argillaceous and_ siliceous impurities  charac- 
terize the western exposures, and these are marked by a single hori- 
zon of carbonaceous beds associated with land plants. As it is under- 
laid by limestone and immediately overlaid by limestone, both deep-sea 
deposits, it is evident that this episode of dry land was a moment of true 
elevation. 

At the close of the deep-sea lime-period came a third great stratigraph- 
ical division of the Palzeozoic—Weber quartzite—a body of pure siliceous 
detritus from 6,000 to 10,000 feet in thickness, characterized by conglom- 


536 SYSTEMATIC GEOLOGY. 


erates both in the near neighborhood of the granitic islands and close to the 
Nevada shore. 

This is immediately succeeded by the fourth group or Upper Coal 
Measure limestone, a body about 2,000 feet thick of strictly pelagic material. 

The whole Paleozoic, therefore, may be summed up as to its material 
as two periods of mechanical detritus, interrupted by one and followed by 
another period of deep-sea lime-formation. While in the conglomerates 
which appear in all the siliceous members of the series we have evidence 
of episodes of shallow waters, yet the occurrence of 13,000 feet of limestone 
indicates enormous intervals of the continued sway of profound ocean. 

When compared with the corresponding series, as displayed in the 
Appalachian system, it differs, first, by the absence, as it thus far appears, 
of those not infrequent orographical disturbances which render the Appa- 
lachian Paleozoic groups repeatedly unconformable among themselves; 
secondly, while land areas were common from the close of the Devonian 
in the east, and the materials fail to show any great continuance of ocean 
sway in the region of the Appalachians, in the Cordilleras there is evidence 
of but a single temporary land episode, and that most restricted in its area. 
Taken as a whole, the Palzeozoie was distinctly an age of ocean sway. 

Accompanying this chapter are two tables, Nos. VI. and VIL, in which 
are given analyses of the members of all the sedimentary series whose con- 
stitution seems to afford a chemical interest. The tables are divided into, 
first, the deep-sea and lacustrine limestones and the composite calcareous 
Tertiary and Cretaceous rocks; secondly, siliceous and pure detrital rocks, 
the sandstones, quartzites, &c. 

It is not intended in this chapter particularly to discuss the character 
or causes of those mechanical movements in the solid earth which succes- 
sively elevated and depressed various portions of the Cordilleran area; but 
it is impossible adequately to conceive of the stratigraphical grouping 
without a passing mention of those mechanical events. After the close of 
this great conformable Paleozoic deposition, wide-spread mechanical dis- 
turbance occurred, by which the land area west of the Nevada Paleozoic 
shore became depressed, while all the thickest part of the Paleozoic de- 
posits from the Nevada shore eastward to and including-the Wahsatch, 


STRATIGRAPHICAL RESUME. Se7/ 


rose above the ocean and became a land area. Between the new continent 
and the old one which went down to the west, there was a complete change 
of condition. The land became ocean; the ocean became land. In the 
rising of the Paleozoic, however, the elevation proceeded no farther east- 
ward than the Wahsatch. East of that point, the Upper Carboniferous 
beds were still the undisturbed ocean-bottom; but instead of receiving 
sediments either from the destruction of organic life within the ocean area 
or from the distant continental sources to the west, the newly elevated 
land-mass, extending from the Wahsatch west to 117° 30’, became the area 
from which was derived the post-Carboniferous detritus to form the great 
Mesozoic series that, east of the Wahsatch, were laid down conformably 
upon the still submerged and still undisturbed Carboniferous. 

Upon the western side of the new land-mass, the Archean continent, 
having gone down, made a new ocean-bottom, and upon this immediately 
began to accumulate all the disintegration-products of the new land-mass 
which the westward draining rivers and the ocean waves were able to deliver. 
Throughout the Triassic and Jurassic periods the western ocean was accu- 
mulating its enormously thick group of conformable sediments upon an 
Archean floor, while east of the Wahsatch, in the mediterranean ocean, the 
sediments of the Trias and Jura were accumulating conformably upon the 
Carboniferous; until, at the close of the Jurassic age, there had accumu- 
lated in the western sea 20,000 feet, and in the mediterranean sea 3,800 
feet, of Triassic and Jurassic material. 

The comparison of the Trias-Jura series, in these two separated seas, 
shows two things: first, that the western sea was very deep during the 
Trias; secondly, that the mediterranean was shallow during the Trias. In 
both cases the first half of the Trias was prominently a period of the recep- 
tion of pure detritus, while the second half, especially in the western ocean, 
was characterized by the liberal intercalation of lime. The Jura, especially 
in the east, was an age of shallows, and its materials were almost altogether 
of clays and shales and shaly limestones. At the west, the lower members, 
as at the east, were prominently calcareous; but later, and closing the 
series, is an unknown thickness, certainly over 4,000 feet, of fine argillites. 

At the close of the Jurassic age the western ocean, with its original 


538 SYSTEMATIC GEOLOGY. 


floor of Archean ranges overlaid by twenty-odd thousand feet of conform- 
able Trias-Jura sediments, suffered abrupt orographical uplift, resulting in 
the formation of a series of sharp folds and elevating a portion of the ocean 
area, extending from the eastern shore outward and westward as far as the 
present west base of the Sierra Nevada, making an addition to the conti- 
nent of 200 miles, the Sierra itself constituting the most western and most 
elevated of the newly formed mountain ranges. The character of the 
orography of this period of disturbance is that of tangential compression, in 
which the gentler action was close to the old shore in the meridian of 117° 
and most powerful in the crumpled western slope of the Sierra Nevada, 
where the Triassic and Jurassic series have their enormous thickness 
crushed into a mass of almost indistinguishable folds, the rocks thrown into 
vertical dip and crowded together, making a belt of strata about fifty miles 
broad. This orographical action continued southward as far as the defined 
range of the Sierra Nevada extends, and northward along the whole shore 
of the Pacific, probably as far as the Alaskan peninsula. Passing north- 
ward from the region of the Fortieth Parallel, where the new addition to 
the continent measured about 200 miles from east to west, the zone of 
crumpled Mesozoic was depressed so that the new ocean shore at the begin- 
ning of the Cretaceous age touched the west base of the Jurassic fold of 
the Blue Mountains of eastern Oregon. 

While this powerful dynamic action was taking place on the west side 
of the land area, there still remained, so far as upheaval, subsidence, or 
folding is concerned, a complete calm in the region east of the Wahsatch. 
The uppermost shaly members of the Jurassic from the Wahsatch out to 
Kansas are immediately conformably overlaid by the basal members of 
the Cretaceous. 

The revolution which produced this great change in the configuration 
of the country, although not recording itself over the area of the mediter- 
ranean ocean in any disturbance or nonconformity, was, however, sig- 
nalized by a complete change in the character of the sedimentary material. 
The phenomena of the Cretaceous west of the boundary of California did 
not fall within the study of this Exploration, and have already been de- 
scribed by Professor Whitney in the Geology of California. Since the close 


STRATIGRAPHICAL RESUME. 539 


of the Jura no marine sediments have been laid down between the west base 
of the Sierra Nevada and the Wahsatch. 

During Cretaceous time the mediterranean ocean stretched from the 
eastern base of the Wahsatch into Kansas; and over the entire bottom of 
that body of water, with the exception of a few Archzean islands, which 
were still, as they had been throughout the previous ages since the begin- 
ning of the Cambrian, lifted above the plane of deposition, a continuous 
conformable sheet of Cretaceous sediments was laid down. Its greatest 
thickness was against the western shore of the ocean, namely, against the 
eastern base of the Wahsatch, where conformably over the top of the Ju- 
rassic shales are about 12,000 feet of Cretaceous beds. Passing east- 
ward, this series in the province of the Great Plains near the eastern base 
of the Rocky Mountain system has thinned to 4,500 or 5,000 feet, and in 
western Kansas it reaches its thinnest development as described by the 
Geological Survey of that State. 

The materials of the underlying Jura are all of excessively fine grain. 
Conglomerates are absent except on the immediate foot-hills of the Wah- 
satch. ‘The fine summit shale-members of the Jura were immediately suc- 
ceeded by a coarse siliceous conglomerate which stretches in an uninter- 
rupted sheet from the base of the Wahsatch nearly to the easternmost 
exposures of the Cretaceous beds. The pebbles immediately bordering the 
Wahsatch are, in some instances, a foot in diameter. Farther east they 
gradually thin down to the size of a filbert, and in the region of Kansas are 
no longer to be seen. 

In the extreme western Cretaceous exposures in the territory of Wah- 
satch and Uinta ranges, coal-beds appear at the very base of the series im- 
mediately upon the capping members of the Jura; and from that horizon 
to the summit of the series, throughout the whole 12,000 feet, they recur 
in that region. They increase in frequency after the close of the Fox 
Hill group, and are most abundant through the 4,000 or 5,000 feet of the 
closing or Laramie group of the series. The deduction from these fre- 
quent coal-beds is clearly that of land areas and of repeated subsidence 
throughout the whole Cretaceous age over the western part of the Cre- 
taceous area. 


540 ‘ SYSTEMATIC GEOLOGY. 


In the region of the Great Plains, coal-beds are unknown below the 
summit of the Fox Hill. Beneath that horizon there is no evidence of a 
land surface in the eastern part of the Cretaceous field. The series, there- 
fore, below the top of the Fox Hill was purely an ocean deposit in the 
region of the Rocky Mountains, but in the region of the Wahsatch was 
frequently above the limit of the marine waters, carrying upon its surface 
abundant vegetation. 

Throughout the whole Cretaceous, below the top of the Fox Hill, the 
molluscan fossils are invariably marine, with the exception of certain inter- 
calated groups of purely fresh-water shells near the region of the Wah- 
satch, which, from their position close to the Cretaceous ocean shore, are 
evidently the in-washings of a fluviatile fauna. 

Regarded as a whole, the basal member is a single sheet of siliceous 
sediments and rounded conglomerates from 300 to 500 feet thick. Over 
this lies the great Colorado group, 2,000 feet thick in the west, 1,000 feet 
thick in the region of the Great Plains, made up chiefly of fine caleareous 
and argillaceous material, which toward the middle of the group is promi- 
nently formed of marls or limestones. 

Above the horizon of the Colorado group the Fox Hill and Laramie 
are essentially of sandstones, about 9,000 feet in thickness in the region of 
the Wahsatch, about 3,000 feet in the region of the Great Plains. At the 
very summit of the uppermost or Laramie group are found Dinosaurs. 
The fauna up to the base of the Laramie is strictly marine. The Laramie 
itself carries the remains of an estuarial or brackish-water life, associated 
with strictly Mesozoic Saurians. With the close of the Cretaceous the con- 
formable series of marine and estuarial deposits east of the Wahsatch come 
to an end, and the last moments of deposition were immediately followed 
by one of the most important orographical movements of the whole Cor- 
dilleran history. 

From the eastern base of the Rocky Mountains to the eastern base of 
the Wahsatch the whole region was thrown either into wide undulations 
or sharp folds. So great a range as the Uinta, with its distinct, broad, flat 
anticlinal, was made at this period. Relatively to the present basin of the 
Colorado, the whole chain of the Rocky Mountains was elevated so as to 


STRATIGRAPHICAL RESUME. 541 


define a broad, shallow depression, which now includes the waters of Colo- 
rado River. Powerful and important as this orographical movement was, 
it failed to disturb the coast deposits of the Pacific in California; but from 
reasons already given it seems probable that the first definition of Cascade 
Range was caused by its force. In the general geology of North America 
the most important result of this immediately post-Cretaceous orographical 
movement was the elevation of the whole interior of the continent and the 
complete extinction of the inter-American mediterranean ocean. 

From the date of this movement no marine waters have ever invaded 
the middle Cordilleras, and the subsequent strata are all of lacustrine 
origin. The effect of this orographical movement was to leave that part of 
the Cordilleras which falls within our study with a free drainage to the sea, 
with the single exception of the basin of Colorado River, which, from its 
configuration, immediately became the receptacle of the vast fresh-water 
Ute Lake, within whose area accumulated the important Vermilion Creek 
group, the earliest of the fresh-water Eocene strata. Throughout the entire 
Eocene period the basin of Colorado River was the theatre of a series of 
four Eocene lakes, whose deposits—unconformable among themselves, as 
has already been described—amount in all to 10,000 feet; lacustrine rocks 
characterized from the bottom to the top by an abundant series of verte- 
brate life covering the whole lapse of Eocene time. The Eocene of the 
Fortieth Parallel region was a period of four lakes superposed, the uncon- 
formity of their deposits due to four orographical disturbances. 

An important orographical movement took place at the close of the 
Eocene, by which the province of the northern Great Plains and a long, 
narrow tract of Washington Territory, Oregon, Nevada, and California, 
lying on the eastern base of the Sierra Nevada and the present Cascade 
Range, became depressed and received the drainage of the surrounding 
countries, forming two extended Miocene lakes. The deposits of the west- 
ernmost lake are chiefly the tuffs and rearranged ejecta of volcanic eruption. 
The deposits of the Plains are the simple detritus from the surrounding 
lands. The series on the west are over 4,000 feet thick; in the east they 
are not proved to be over 300 or 400 feet. Both contain abundant and 
typical Miocene vertebrate life. 


p42 SYSTEMATIC GEOLOGY. 


The close of the Miocene was signalized by a powerful orographical 
movement over the area of the western Miocene lake, which threw 
the beds accumulated on its bottom into folds. Contemporaneously with 
this movement the Miocene lake of the east, by the subsidence of the 
surrounding country, increased so as to cover the whole province of the 
Great Plains. 

The Pliocene opened, therefore, with two enormous lakes, one covering 
the basin country of Utah, Nevada, Idaho, and eastern Oregon; the other 
occupying the province of the Plains. The Pliocene deposits of the Plains 
lake are caleareous and sandy beds, which have no angular nonconformity 
with the underlying sheet of Miocene sediment, but which overlap it in 
every direction. The deposits of the great western lake are nonconformable 
with the Miocene and immensely overlap it to the east, doubling the area 
of Miocene sediment. Both of these Pliocene lakes—as do the Miocene— 
contain the remains of rich faunz. The eastern lake received a maximum 
of about 2,000 feet of strata; the western lake has nowhere shown over 
1,400 feet. 

The close of the Pliocene was signalized by another orographical move- 
ment, which threw the sediments of the Great Plains lake into their inclined 
attitude, dipping 4,000 feet to the east and 7,000 feet to the south from the 
Fortieth Parallel region. This same orographical movement acted differ- 
ently upon the sheet of sediments which covered the Pliocene lake of the 
Great Basin. Instead of tilting the entire lake, it broke in the middle, and 
the two sides were depressed from 1,000 to 2,000 feet thick, the shores 
faulting downward. The result of the post-Pliocene movement in the 
department of the Plains was to give thereafter a free drainage to the sea. 
The result in the area of the Great Basin was to leave two deep depressions, 
one at the western base of the Wahsatch, one at the base of the Sierra 
Nevada, which, in Quaternary times, received the abundant waters of the 
Glacial period and formed the two lakes that have already been described 
in the Quaternary chapter. 

In summing up the general stratigraphical results of the section, 
it will be seen by referring to the tabular statement at the end of this 
chapter that there is exposed, from the bottom of the Cambrian to the close 


oaRA 


*stsd[vur 


jo raquiny 


| 


(3) 
Ks) 


ne) 
So) 


64 


7° 


fi 


TABLE OF CHEMICAL ANALYSES. VI—AW—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. 
SEDIMENTARY ROCKS. 


Limestomes. 
é Ca, Mg, and € 
Locality. Formation. Analyst. 4 At Fe Ca Mg (e H Total. combined. 
I ae a 
4 Ca C|Mg€ 
: = —_ + — ; 
62 | Conglomerate ridge, east of Bear | Pliocene- - | Wyoming conglomerate] B. E. Brewster - | 12.30 0.78 47-01| 0.49 | 37-08] 2.41 Dro! oto 100.07 | 83.05] 1.03 
| River. 
: Es : 6 ims 
63 | Garden Valley Tertiary - - - - ce - -| Humboldt - - - - = - | 12.07] 1.28 | 0.57 | 45.29] 1.86 | 36.23] 2.65 | Na} 2-90 100.85 
K 
12.11] 1.50] 0.44 | 45.30] 1-83 | 36.23] 2.67 | Na fost Too:93 || « = 6 
| —~_—=. - . 
64 | Chalk Bluffs- - - - - - - -| Miocene- - | White River - - -|R.W. Woodward] 1.49] . %| 0.37 | 54-16] 0.15 43.68 Mn o.15 100.00 
ea - 
I-62) sue | 0-31 | 54.18] 0.15 43-69 Mn 0.15 160.00 
_—_— 
6s | Upper stratum, Valley Wells - - «_ - -| Truckee- - - - -|B.E. Brewster - | 32:02 0:43 35-82] 0.36 | 29.16] 2.10 Chin os 6 99:99 
| ae 
66! Reed’s Hill, near Carson River, east @ - - Gs Seo 5 S 5 Us - G6 0.10 53:99| 1-25 | 43:80] 0.86 Gm oh. 100.00 
end of Triangular Range. { 
| ij 
67 | Fossil Hill, Hot Spring Mountains w - - G Se oo 6 Gi - | 7-38} 0:80}| 0.68 | 48.53] 2.46 | 40.86] . . PO® 0.16 100.86 
| 
j ‘ ‘ 
68 | Bridger Beds, Henry’s Fork- - - | Eocene - -| Bridger - - - - - as - | 31-28] 1-83)! 0.22 | 34.20] o.11 | 26.79] 4.64 |K 0.33 Nao.18] 99-58 
31-45 75a) 0.21 | 34.18] 0.08 | 26.82] 4.64 |Ko.33 Nao.28| 99.56 
i : 
Go| Green River shales -- - - - - « - -| Green River - = - Gi - | 29.22 0.76, 2.16 | 33-53] 0.56 | 27.08) 6.27 {Na } 038 99:96 
| im 
29-19} 0:87)| 2.20 | 33.57| 0.68 | 27.03] 6.20 {Xa fo38 10012] - 
| 
7° | Brush Creek, spheerolitic sandstone | Cretaceous - | Colorado - - - - a - | 2/).5 8) eared | Deca Sete + + | 43-90 
| 
71 | Dry Creek, blueshale - - - - « 2 « ea ners « Sieo o|| o 7 Aeon of ao ofl oo Oso 9 ao | Gs) 
—_S-_—_. 
72 | WotR sos > 5 = 6 sll inegiiec slo - 2 os so oo “ =| Gsar Q.92 50-57| 0.36 | 40.18] 1.50 Gao. o- 4 100.08 | gt.11] 0.75 
eet K 
73 | Laramie Plains- - - - - - - Ge ies ko oa Sa eS « =| 2.77 0:79 29-90] 19.31 | 45.05] 1-35 {Na }o38 99:55 | 53:40) 40-55 
2.95 O54 29-69 | 19.36 | 45-14] 1.30 {Na } 028 99-42 | 53:02] 40-66 
3 (*) ; 
SiO, - - - - - = = = 23:4 
Ah O; - - - - - - = = 5:40) 
CaO - - = = = = -eaamomts 
MgO - - - --- = - 0.06 
6z.19 


TABLE 


Number of 
analysis 


~ ~ ~ 
n wm - 
Qi aa) 
a [SJ zhu 


TABLE OF CHEMICAL ANALYSES. VI—B.—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL 
SEDIMENTARY ROCKS 


Limestomes—(Continued.) 


s ., 8 Ca, Mg, and C 
22 Locality. Formation. Analyst. 4 At | Fe | Ca | Mg H Total. pues 
Be e Ca€ |MgC 
| 
74 | Divide between Cottonwood and | Triassic - - | Star[Upper] - - - | B. E. Brewster - 1.61 0.26 52-16] 2.47 | 43-70 PO trace. 100.20 
Union Canons. | 
75 | Ravine north of Wright’s Caion, fs - - ce So oS G S|} AH7 0.119 51-69] 1-04 | 41.75], 0.84 PO* trace. 100.00 
West Humboldt Range. } 
76 | Greenish limestone below Upper ws - -| Red beds [Lower]- - - | 13-46 1.63 36-78] 8.44 | 38.31] 2.04 Mn O 0.20 100.86 | 65.68] 17.72 
Red, East Fork Du Chesne, Uinta 
Mountains. 
7 | Rese 5 2 = 5 5 5 5 ere co ae SS s =| 222% 0.21 43-24] 0-15 | 33-94] 0-14 99:89 | 76.75] 9.32 
78 | Summit of Tenabo- - - - - ~- | Carboniferous! Upper Coal Measures - Gs - | 20.99 1-09 39:76| 2.80 | 32.80] 1.06 Fe S? 1.16 99-66 | 67-54] 5.88 
79 | Clover Peak Range - - - - - ss a3 a = cs -| 2.71 0-27 30:39 | 20-07 | 45-72] 1-71 100.27 | 53:75] 42-14 
80 | Vermilion Gap Rocks, lower series fe “ Gs - as - || 2.02 0.54 54.06] 0.34 | 42.85] 0.41 F 100.25 | 96.54] 0.71 
81 | Ridge west of Green River, between a £ g - fe - | 27-93 0-35 39:54| 0.28 | 31.69] 0.25 6 100.04 | 70-61} 0.60 
Uinta quartzite and Canon sand- 
stone. 
82 | Granite Canon, Black Hills - - - f § ce - | R. W. Woodward} 0.34 0.16 34-95 | 17-36 | 46.55) 0.23 100.11 
83 | East slope of Black Hills - - - Gh Lower Coal Measures - | B. E. Brewster - \. A. bro 99:29 | 60.09) 39-20 
84 | White Pine limestone - - - - - Lo a a3 - |O.D. Allen - -| 0.70 55:38| 0.25 | 43-70 100.03 
0.70 55-32] 0:26] = = 
85 | North of Maggie Creek Gap, Nevada a a ig - | B. E. Brewster - | 4.36 0.44 53:17 | 0.36 | 42.10 PO; trace. 100.43 
86 | Humboldt Mountains- - - - - a fe us - G =| 1-35 0.36 54-51] 0.27 | 43-13] 0-11 PO® 0.35 100.08 | 97-34] 9-57 
87 | East Humboldt Range - - - - (a @G G = c - | 37-037) I-51 }0-59 | 33-29| 0-75 | 25-57] 9-39 ie eet 99-43 | 56-25} 1-56 
—_— 
88 | Peoquop Range - - - - - - aw c “e - ce - | 34-919 0.38 34.33 | rer2 | 27.772 PO? trace. 99-76 | 60.32] 2.34 
89 | City Creek limestone - - - - - te is « 2 ce = || yy 0.24 53:09] 1-20 | 42.88] 0.21 PO® trace. 100.00 | 94.45] 2.52 
go | Fossil Hill, White Pine Mountains | Devonian -|- - - - - - - - « = 1-23 0.39 54-06] 0.71 | 43-29) 0-34 . 100.02 | 96.53 1.48 
gi | Underlying limestone, Muddy Creek | Silurian - -|- - - - - - - - “« Ey | 6:1738 0.60 43-23] 2.18 | 36.20] 1.17 | PO® o.12 100.23 | 76.82) 4.58 
1 
2 3 1 4 
SiO, - - 18.99 SHO; = = siesa Si O, - 13.45 
AIO; = = 5:79 AN,O3; = = 2.45 Al; O73 ase 
FeO; - - 2.23 MgO - - o.12 1 
CaO - - 4.43 Loss - - o8r | 16.57 
MgO - - 3.90 ; 
34:92 | 


» 
nas 
\\ 
Ni 
\ 
oe , 
=) 
_ 
a i} 7 
—) 
\ 7 
as 
= > 7 

_ _ 


i) 
a3 Locality. Formation. Analyst. Si 
Es 
a 
g2 | Cache Valley - - - - - - -| Pliocene- - || Humboldt - - - - |B) E. Brewster - 04-44 
93 | South slope, Uinta Mountains - - | Eocene - -]| Uinta - - - - = Gs - 
94 Troyes Wee = = 5 > 5 = = “6 - -| Green River - - - “ “ 
95 | Cathedral Bluffs, Wyoming - - - us oa « ieee “ : 
96) Black Butte- - - - - - - -| Cretaceous - || Laramie- - - - = & = 
97 | Ashley Creek, Uinta Mountains - Us =|] Wor Isis s S 5 ¢ & ‘J 
98 | Saint Mary’s Peak, Wyoming - - a = ce Sos 6c “ z 
99 | Camp Walbach- - - - - - - Gs =| Dakota: fcocctes rowel “ 2 
1co | Red sandstone, Uinta Mountains - | Triassic - -]- - - - - - - = “ z 
ror | Divide between Cottonwood and ee ee ta ey onreaco 3 “ z 
Unionville Canons. 
102) | (Coyote Canon = = = = = = = G3 slo = oe eo o oc “ es) 
5 
103 | Near Cottonwood Canon, West CS) abe a eo ch ee B - 
Humboldt Mountains. 
104 | Cottonwood Canon, West Hum- ue oul eo ee eS 5 & = 
boldt Mountains. 
105 | Weber Cation, below Narrows, Wah- PRS ce ol cy SS 55 Ss - 
satch Mountains. : 
106 | Anthro’s Canon, Uinta Mountains - ce Baio oe ade ao; Sc “ = 
107 | West Ridge, Battle Mountain - - | Carboniferous) Upper Coal Measures - va = 
+ Insol.res.! 66. 
Cabin Quarry, Upper Weber - - « “« “ 2 “ Nee ee ala 


Top of Parley’s Peak, Wahsatch 
Mountains. 


“ “ 


Insol.res.* 60.75 


Sol. Si 


0.2T 


AT ae ee 
pf intra, 


a 
birth 


1 


i 


TABLE OF CHEMICAL ANALYSES. VI.—B—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. 
SEDIMENTARY 


Quartzites, Samdstomes, and Associated @ccursemces—(Continued.) 


ROCKS. 


S a ay i 
ae Locality. Formation. Analyst. Si At Fe Fe Ca | Mg | Na K ¢ H Total. 
z* | 
110 | Pilot Peak, Ombe Range, Nevada - Carboniferous| Weber Quartzite - B. E. Brewster - 94-93} und. | und. 0.17 95-10 
111 | Big Cottonwood Cation, Wahsatch ce a is = cs 95-81) und. | und. und. 0.28 96.09 
Mountains. | 
Irz | Weber Ganon = = = = = = Gs Us w - 82.99) fr. tr. und. | und. 5-47 88.46 
113 | Point Carbon, East Forkof DuChesne es iw - se 97-63] und. | und tr. 0.58 98.21 
114 | Agassiz Amphitheatre- - - - . g - is - 98.58] und. | und. 0.17 98.75 
115 | Carico Peak, Nevada- - - - G | co as - - fe 97-59| und. | und. 0.18 9177 
116 | Bear River, Geodetic Point- - - “e fe ig ce : 87.47 7-47] 0.26 0.20 | 1.30 | 2.53 0.56 99-79 
87-42), - > T.09 | 2-73 0.45 “oats 
117 | Ogden Canon, Wahsatch Mountains | Devonian Ogden - - a 4 we - 97-79) und. | tr. 0.15 97:94 
118 | American Fork Cation, Wahsatch ut i > 8 2 = 89:75 2.38 92.13 
Mountains. 
11g | Three Lakes, Wahsatch Mountains | Cambrian oo (9. oc os a 59:96| und. | tr. tr. 3:16 . 
Irom-stome. 
— — 
120 | Near Carbon, Wyoming - - - - | Cretaceous Colorado - SS = 9:74] 5:57| 1-93 | 38:67| 7:64 | 1.20 0.46 32:04 Mn O 2.38 99-63 
Infusorial Karths. 
121 | Little Truckee River, Nevada - - | Miocene - Truckee - - - - | R. W. Woodward 91-43] 2.89 0.66| 0.36 | 0.25 | 0.63 | 0.32 3:80 100.34 
gi-51 2.95 0.63 0-39 0.20 0-59 0-23 3:79 100-59 
122 | Fossil Hill - - - - - - - - Wi! a - - o 5 Ws 86.70) 4.09 | 1.26] 0.14 | 0.51 | 0.77 | O.4t 5:99 RO? und. 99:87 
86.91] 4-00 1.22| 0.11 | 0.51 | 0.80] 0.36 5-89 PO® und. 99:80 
123 | Fossil Hill - - - - - - - - Gs GO oe 5 - -|B.E. Brewster - 98.06 0.62 98.68 
Greem Earth. 
Oo © 
124 | Grizzly Buttes, Bridger Basin - - | Eocene - ee - -|R.W. Woodward 66.17} 14-95] 2.76] 1.95] 3.89 | 1.88] 2.84 | 3.77 2.61 O > trace. 100.82 
(6) ; 
66.42| 14-73] 2.82] 1.93] 3-89 | 1-97 | 2-97 | 3:65 2.57 O ¢ trace. 100.91 


STRATIGRAPHICAL RESUME. 543 


of the Tertiary, a total thickness of about 77,000 feet of beds. About 
19,800 feet are limestone, while the rest is purely detrital. 

In the Cretaceous and Tertiary a considerable chemical proportion of 
the detrital beds is lime, but they are distinctly detrital formations, and the 
lime is the disintegration of already crystallized limestone. Embraced 
within the 19,800 feet of limestone are 1,500 feet of calcareous shales and 
shaly limestone of the Green River middle Eocene group. 

The great Pogonip Cambro-Silurian bed of 4,000 feet is prevailingly 
siliceous, and is characterized by a small, variable percentage of magnesia. 

The Wahsatch limestone, 7,000 feet thick, the greatest single calca- 
reous body in the series, is for the most part a normal limestone, mechani- 
cally impure at a variety of horizons by the inclusion of siliceous or 
argillaceous particles, and in the lower beds, especially in the region of the 
Waverly and parts of the Devonian horizons, chemically impure by the 
admixture of carbonate of magnesia. 

True dolomites in thin sheets are found in both the Pogonip and Wah- 
satch bodies, but neither chemical nor microscopic analysis discovers a 
considerable general distribution of magnesia in these two great series. 

The Upper Coal Measure limestone, 2,000 feet thick, is comparatively 
pure, its chief admixture being argillaceous and siliceous sediments. 

The series of intercalated limestone beds, amounting in all to about 
5,000 feet in the Alpine Trias of western Nevada, is noticeable for the large 
amount of carbon which it contains, the comparatively small amount of 
magnesia, and the constant, but slight, proportion of quartzose and 
aluminous sand. 

Above the limit of the upper Trias, throughout the entire Cretaceous 
and Tertiary, the limestones are all fragmentary and are simply the pul- 
verized sands which are worn down from the neighboring limestone mount- 
ains. 


544 TABLE OF STRATIGRAPHICAL GEOLOGY. 


QuareRrvany } Upper Quaternary .-.....---- | Gravels and loose subaerial detrital material. 
Lower Quaternary ....--..--. | Fine muds and silts. 
Man oc ONG Coarse structureless conglomerate. 
Niobrane { Gearee and fine friable sandstones, and siliceous limestones; 
Pai Goer a: eed eae horizontal where observed. 
Generally siliceous, fine-grained, friable beds; frequently vol- 
| Humboldt ....... § canic taffs ; undisturbed. : eae ¥ 
(a) en . . 
& 3 | North Pare eer and limestones, loosely agg'‘omerated; undis- 
ot 
3 y pone { Truckee Seely, f ett! limestones, gravels, and volcanic (palagonite) tutfs; 
| Q] Terriary.....- \ Miocene . 2 S 
SS | white River. .... | Fine light-colored sandstones, with clays interstratified. 
(= Coarse and fine pinkish sandstones, gravel conglomerates, and 
Uinta. .-.-------- ; argillaceous beds. he = : 


Bridger .....-..-. f Drab thin-bedded sandstones, and green marls, rich in verte- 


Eocene .. brate remains; slight development of limestones. 


Thin calcareous shales, with fishes and insects; buff calcareous 


Green River ..... j sandstones, and lignite toward the baso. 


ie _ §Coarso pink and chocolate-colored sandstones, with large de- 
| Vermilion Creek. f velopment of conglomerates. Ooryphodon beds. - 


Coarse white aud reddish sandstones, heavily bedded, with large 
; dovelopment of coal seams. Fossils marine and brackish- 
water. Unconformable with foregoing series. 


pe ee ee 
iva Speen § Coarse white sandstones, heavily bedded ; few coal seams ; less 


CRETACEOUS ... iron than former; fossils marine. 


Mostly blne and yellow clays and marls, with thin sandstones. 
cmeen #ozseeeColarado-+-+-=- 4 Coal. Fossiliferous. “ 


Gee eee Dakota ....-.-.-. | Sandstones and characteristic conglomerate, 


development. 
renrs, srrtrrccscesceeecseeeeee*) Tn Novada, Heavy limestones, shales, and argillites; greater 
l development. 


East of Wahsatch. Clays and limestones; fossiliferons; small 
JURASSIC....... j 


MESOZOIC. 


erous blue limestones, tire development of Triassic rocks 

interstratified with| eastof the Wabsatch, consistmainly 

Star Peak........{ quartzitic schists and of coarse, heavily-bedded sandstones, 

DIGYABRIG2 on asss Red Beds slates. of prevailing red color, sometimes 
white or buff, with some clays, thin 

limestone beds, and frequent depos- 

aston argillites,and| its of gypsum. Almost barren of 

porphyroids. ) fossils. 


Heavy - bedded, fossilif-) The Red Beds, which represent the en- 


Koipato.-. 


Permo-Carboniferous .....--. | Clays and argillaceous limestones, with ripple-marks. 


In general, light-colored blue and drab limestones, more or less 
Upper Coal Measures...-.--- siliceous, and passing in places into sandstones ; generally 


fossiliferous. 


Weber Quartzite ..-.-...--.- with local developments of interstratified calcareous and 


CARBONIFEROUS eth sandstones and quartzites, frequently of reddish colors, 
argillaceous beds and conglomerates; non-fossiliferous. 


Lower Coal Measures. -...--- Heavy-bedded blue and gray limestones, with some 
Wahsatch interstratified quartzites, more frequently in the 


J limestone. upper part of the series. Lower beds siliceous 


(Sub-Carboniferous........... 


PALZZOZOIC. 


32,000 + ft (Wahsatch section). 


( Nevada Devonian at times. Fossiliferous. 
DEVONIAN 3.222490 0 = rns 7 7 = a ; 
) Ogden Quartzite. .........--. be pret petty quartzite, pink tints; conglomerate with 
SILURIAN ...... | Ute-Pogonip limestone. .....- Compact blue limestone, with included argillites, passing into 
Somat ss] = teal iplimestone......- | caleareous shales. More largely developed in Nevada, where 
(Pogonip ..... 2.22. ccieseees j the limestone carries primordial fossils at the base. 
renee J > whi i jron-stained, with 
Cc Noe Generally white quartzites, more or less _iron-stained, wi 
aes i Soon aeiiwase cc veameeeeee poceccn ; some development of micaceous beds, and heavy dark-blue 
argillites. 


wee SE seri 8 es 
FIGRONIAN|: os saacee weweleseatadeece ea perme p nies granites, diorite-gneisses, argillites, 
ioe ee limestones, and quartzites. 


50,000 + ft. 
ARCHATAN. 


LAURENTIAN 22-2 eeccceecccccececece Coarse red orthoclase-mica granites, mica-gneisses, and schists. 
BS a cl aaa ; with deposits of ilmenite and graphite. ; 


CHAPTER VII. 
TERTIARY VOLCANIC ROCKS. 


SECTION I.— PROPYLITES — QUARTZ-PROPYLITES. 

SErcrion IIl.— HoRNBLENDE- A NDESITES — DACITES— AUGITE-ANDESITES. 
SEcTION II].— TRACHYTES. 

SECTION I1V.— RHYOLITES. 

SECTION V.— BASALTS. 

SECTION VI.— CORRELATION AND SUCCESSION OF TERTIARY VOLCANIC Rocks. 
SEecTION VII. FusION, GENESIS, AND CLASSIFICATION OF VOLCANIC ROCKS. 


See C al eOeNe as: 
PROPYLITES AND QUARTZ-PROPYLITES. 


It is the purpose of this chapter to assemble the more important facts 
accumulated by our Exploration relating to the Tertiary voleanic rocks, 
their sequence, geological dates, mode of occurrence, reciprocal relations, 
and petrographic* distinctions, and to offer an hypothesis which it is hoped 
may serve to advance our knowledge of the genesis and classification of 
volcanic species. The material will be classed under three groups: 

First, the detailed occurrence of species, covering sections I. to V., in- 
clusive; and in this the past method of treatment will be continued, namely, 
to begin with the earliest form and describe its special occurrences, passing 
always from east to west. 

Secondly, the larger laws of occurrence contained in section VI., the 
relations of each rock to the orographical actions which brought it to the 


*All purely microscopic details are hereby credited to Vol. VL, by F. Zirkel. 
35 K od 


i 


546 SYSTEMATIC GEOLOGY. 


surface, with such generalizations as seem to be warranted as to synchron- 
ous extravasation of each species, and the superposition and succession of 
all the species. 

Thirdly, in Section VIL. the origin of igneous fusion and the genesis 
and petrological classification of voleanic rocks. 

The area of the Fortieth Parallel has proved exceedingly rich in vol- 
canic rocks. Although but a small part of the actual surface is covered 
with ejecta, yet, as compared with other wide regions, it is distinguished 
by the presence of a very great number of volcanic outbursts. Were the 
Quaternary valley deposits removed, together with a considerable portion 
of the most recent Pliocene, the area of volcanic rocks would be greatly 
enlarged over the western part of Nevada. Reference to Analytical Map 
VIL, at the close of this chapter, will show at a single glance the area cov- 
ered and the distribution of species. 

At the close of the Jurassic age, a powerful mountain-building period 
was characterized in Nevada and Utah by scattered ejections of middle- 
age eruptive rocks, including diorite, diabase, felsite-porphyry, and horn- 
blende-porphyry, together with rare melaphyres. That these rocks were 
post-Jurassic is clear from their covering Mesozoic strata in western 
Nevada and California. All over the Cordilleras, so far as we know, 
the entire span of the Cretaceous age was one of orographical calm, 
undisturbed either by important mountain flexures, perceptible disloca- 
tions, or the ejection of igneous material. The changes of level which 
may be assumed to have taken place were altogether the subsidences of 
sedimental areas. 

East of Wahsatch Range, the entire Cretaceous series, having a max- 
imum thickness of 12,000 feet, are strictly conformable, and are charac- 
terized by detrital material, and there are no traces anywhere of sediments 
which may be referred to active eruption. The same is true on the west 
coast of California. The marine Cretaceous which skirts the western 
flank of the Sierra Nevada, and has more recently been upheaved in the 
system of Coast ranges, shows an enormous thickness of pure detritus. So 
far as our observation goes, the land-mass which lay between the eastern 
and western oceans, bounded on the east by the Wahsatch and on the west 


PROPYLITES AND QUARTZ-PROPYLITES. 547 


by the Sierra Nevada, has no traces of Cretaceous accumulations, either 
subaerial or stratified. We have looked in vain for fresh-water Cretaceous 
lakes or for early massive eruptions. All the indications we have yet been 
able to obtain, point to the fact that this Cretaceous continent had free 
drainage to the sea, was characterized by the absence of all considerable 
lakes, and was eroded to an enormous extent, but never built up by vol- 
canic material. It is not improbable that sooner or later the traces of small 
fresh-water lake deposits may be found. It would, indeed, be surprising 
if such lakes did not exist of sufficient size to have withstood the subsequent 
erosion throughout the Tertiary and Quaternary periods. The value of 
such deposits, could they be found, can hardly be over-estimated, as this 
land area must have been the habitat of the progenitors of Eocene mammals. 
Such lakes would also, perhaps, solve the question whether over the land 
areas there are any ejections. Until such data shall be discovered, we are 
warranted in assuming that the Cretaceous was a period free from either 
considerable orographical motion or the coming to the surface of any 
igneous rocks. 

The relations of volcanic material to the surrounding sedimentary 
rocks are always among the most perplexing problems offered to the field 
geologist. In the case of the Fortieth Parallel area, after the greatest pains- 
taking, we are still unable definitely to fix the era of the resumption of 
igneous activity. In the extreme east of our area, on the divide between 
North and Middle parks, as also upon Steves’ Ridge in the Elk Head 
Mountains, occur two families of rocks which may not improbably be 
hereafter referred to one group. Those upon Steves’ Ridge have been re- 
ferred by Professor Zirkel to the trachytes. They are quartziferous trachytes, 
composed of sanidin, quartz, biotite, a little plagioclase, and rare hornblende, 
titanite, and apatite. The sanidins are among the most remarkable ever 
observed in voleanic rocks. The crystals are all completed and attain the 
size of an inch cube, and present many of the rare faces which are charac- 
teristic of the older orthoclases of granite-porphyry. All the quartz 
appears in macroscopic grains the size of a pea, which are rich in glass 
inclusions. 

The strikingly similar granite-porphyry from Good Pass, east of Park 


548 © _ SYSTEMATIC GEOLOGY. 


View Peak, between North and Middle parks, is fully described on pages 
68 and 69, Vol. VI. Large orthoclases, possessing the same rare planes as 
in the trachytes just mentioned are associated with quartz grains, a few 
plagioclases, strongly fibrous hornblende, a little epidote, apatite, and 
titanite. The chief difference between these two types of rock is, that in 
the so-called granite-porphyry the quartz contains fluid inclusions, which 
also occur in the fresh portions of the feldspars. Glass inclusions are 
wanting in the Good Pass rock. Otherwise they are strikingly similar, 
and they are totally unlike any other eruptive rocks within our field. 
Through the kindness of Major Powell and Mr. G. K. Gilbert, I have been 
permitted to look at a series of absolutely identical rocks from Henry 
Mountains, Colorado Plateau. Several slides from this latter locality were 
subjected to microscopic analysis, when it was seen that the hornblende 
contained beautiful glass inclusions, while certain of the quartzes contained 
fluid inclusions with moving bubble. The feldspars were the same remark- 
ably developed orthoclases, with the rare planes mentioned by Zirkel, and 
associated with a few brilliantly striated plagioclases. In other words, in 
the Henry Mountain groups, both the types—that of Steves’ Ridge, which 
Professor Zirkel had called trachyte, and that of Good Pass, which he 
referred to the granite-porphyries—were found associated. It is further of 
great interest that in all three of these localities the eruptive rocks are 
either connected with or subsequent to the upheaval of Cretaceous strata. 

Tertiary rocks have not been observed in immediate contact with them 
in our area, and consequently our only clew to their date is, that they are 
subsequent to the deposition of the Cretaceous. From every geological 
analogy we are led to believe that the disturbance of the Cretaceous con- 
nected with the ejection of these peculiar rocks was a part of the general 
disturbance which took place during or posterior to the Eocene. It is in- 
deed possible that the occurrence of these rocks will finally be proved to 
be pre-Eocene; but from the present geological indications we can only 
class them as post-Cretaceous and not improbably connected with the im- 
mediate close of the Eocene period. At the first two localities mentioned 
they partake, on the one hand, of the nature of trachyte, and on the other 
of granite-porphyry. In the Henry Mountain rocks some of the specimens 


PROPYLITES AND QUARTZ-PROPYLITES. 549 


show a clear predominance of plagioclase and hornblende over orthoclase 
and mica. With these forms are associated quartzes containing moving 
bubbles. 

Taken together, the three occurrences show a series of rocks having 
remarkable physical similarity, yet when subjected to microscopical analy- 
sis showing an approach to the diorites, to the granite-porphyries, and to 
the trachytes. It is not a little singular to see this surprising divergence 
of interior constitution with such evident physical similarity and the com- 
mon characteristic of large, highly developed orthoclase crystals. At the 
present writing Iam inclined to group these rocks under one head and 
refer them to a point of time within the Tertiary period, and to insist that 
they show all the specific divergences which will afterward be traced in 
some of the later groups of volcanic rocks. In both cases the geological 
mode of occurrence of these rocks is obscure in the territory of the Fortieth 
Parallel. They accompany the dislocation and upheaval of thick bodies of 
Cretaceous strata. They cut the latter in dikes, and appear as heavy extru- 
sions. The country in both cases is so much covered with soil, the soft 
Tertiary strata are so generally removed, and there is such a dense growth 
of forest, that the unravelling of the exact geological relation is very diffi- 
cult, so that we are obliged to look to Mr. Gilbert’s forthcoming memoir * 
for all the particular geological relations of this interesting group. 

I have mentioned these in this connection simply to show that the 
dawn of volcanic action is at present not fixed by rigid geological dates. 
With the exception of this group of rocks, which is either to be placed 
at or since the close of the Cretaceous, all the other volcanic series are 
referable directly to the Tertiary. 

The remarkable natural sequence of volcanic rocks brought to light 
by the admirable researches of Richthofen has been in every way cor- 
roborated by us. About the time of the appearance of Richthofen’s 
memoir it was the writer’s good fortune to geologize with him in the com- 
plex field of Washoe, where, more interestingly than anywhere else within 
the Fortieth Parallel area, the various families of voleanic rocks were dis- 
played. From that time to the close of our Exploration I devoted much 


* Report on the Geology of the Henry Mountains, by G. K. Gilbert. 


550 SYSTEMATIC GEOLOGY. 


time to examining the geological relations and superpositions of volcanic 
products, and came without hesitation to accept as law the order of se- 
quence laid down by him, which is as follows: 


. Propylites. 
. Andesites. 
. Trachytes. 
. Rhyolites. 
. Basalts. 


Oo eR CF DD ee 


PropyLite.— Wherever we have been able to observe propylite in jux- 
taposition with others of these five eruptive groups, it is invariably the old- 
est. At the southern base of the Mount Davidson group in Washoe the 
great flood of propylitic rocks which deluged the whole declivity was out- 
poured beneath the waters of a Tertiary lake. The material in the region 
of the Daney Mine, and for a considerable distance east and west and down 
toward the valley of the river until it passes beneath the soft Pliocene strata, 
is composed of propylitic tuff, partly arrangcd by water into truly strat- 
ified beds, and partly bedded in a loose manncr, as if it flowed down in vast 
fields of thick mud. The tuff specimens of these muddy bodies are char- 
acterized by the presence of numerous leaves, chiefly willow, which have 
been pronounced to be Tertiary. But we have learned to be a little 
cautious about accepting the evidence of leaves, since the history of the 
assignment of horizons upon plant evidence alone in Utah, Wyoming, and 
Colorado has revealed a series of professional disasters. This is the only 
direct evidence connected with the propylites themselves. 

The science of petrography offers no more interesting example of the 
delicate shades on which lines may be successfully drawn than the case 
of this rock. Richthofen’s subtle observation and great practice as a field 
geologist enabled him to detect the essential characteristics of the habitus of 
this rock, while at the same time he clearly saw its relations to the other 
hornblende-plagioclase species. The subsequent microscopic analysis of 
the rock by Zirkel has firmly established its independence as a species. The 
English petrographers especially have been inclined to deny its existence ; 
but the shade of habitus upon which Richthofen founded his first assertion 


PROPYLITES AND QUARTZ-PROPYLITES. 551 


of the species is so evident in the field of the Fortieth Parallel Exploration 
that there has never been the slightest doubt on the part of Messrs. Emmons 
and Hague and myself as to the identity of propylite. When the large col- 
lection of specimens brought in by us came to be studied microscopically 
by Zirkel, it was found that we had never wrongly assigned a specimen to 
propylite. In certain instances the microscope revealed the presence of 
minute grains of quartz, and the rock thus characterized came to be classed 
as quartz-propylite ; but there was never any doubt as to the generic nature 
of the rock. There was not a solitary instance in which the rock by us called 
propylite proved to be either diorite, andesite, or plagioclase hornblende- 
trachyte. I am careful to mention this fact, not as a guarantee of the cor- 
rectness of our determinations, for that has been placed beyond question 
by the microscopical analyses of Zirkel, but because later in this chapter I 
shall have occasion to discuss what constitutes a species of volcanic rock, 
and the factor which habitus must necessarily play in classification. 
Whether we regard the actual number of exposures or the total area 
of the propylite, this rock is of the least geographical importance. In all 
cases it is associated with later volcanic rocks, and the paucity of its expo- 
sures and its restriction of area are doubtless in great measure owing to over- 
flow by the later species. From the few exposures in our area, we have 
every reason to believe that if the later volcanic rocks had not overwhelmed 
them, the outcrops of propylite would be more frequent and extensive. 
Within the Fortieth Parallel area this rock is confined to the region 
west of the 116th meridian, appearing only in the basin of Nevada—in 
other words, within the boundaries of the Miocene lake. ‘The most 
eastern propylites in our field are found on the meridian of 116° 15’, 
and a little north of the parallel of 41° 15’, in the region of Tuscarora. 
Here a region from three to four miles north-and-south by two miles east- 
and-west, the whole lying north of Tuscarora, is composed of propylite. 
The surface is almost altogether decomposed, and solid outcrops are rare. 
It is overlaid by rhyolite on the north, northwest, and northeast, and at the 
extreme southern end of the outcrop, in the region of Tuscarora, it is 
covered by the thick Quaternary beds of Independence Valley. Upon the 


whole it is, as an outcrop, rather obscure and unsatisfactory. ‘The surface, 


552 SYSTEMATIC GEOLOGY. 


to a depth of three or four feet, is a loose propylitic earth which has been 
worked for placer gold. The solid, normal portions of the rock are light 
ereenish-gray, decidedly porphyritic, with a general earthy texture and 
rough trachytie surface. The predominating mineral is fibrous green horn- 
blende of a light-olive tint. Plagioclase decidedly exceeds the few decom 
posed orthoclases which are present. Besides the fibrous green hornblende, 
there are dark solid prismatic hornblendes scattered at intervals through 
the mass. 

Farther south, at Wagon Canon, in Cortez Range, a little hill to the 
north of the pass, in the midst of quartz-propylites, shows a greenish 
earthy body, of which the hornblende is almost entirely decomposed, and 
the large, dull plagioclases are chiefly kaolinized. A few rather fresh mono- 
clinic feldspars occur, besides which the microscope reveals apatite and a 
little biotite. This occurrence comes to the surface as an island in a broad 
field of distinctive quartz-propylite. 

In the Fish Creek Mountains, at the western base of Mount Moses, a 
belt of granite overlaid by Triassic strata forms the foot-hills, which to the 
north and south are overwhelmed by the enormously thick accumulations 
of rhyolitie eruptions. Where the Triassic rocks pass underneath the 
rhyolites are a few limited masses of propylite which the most recent 
erosion of the rhyolite has laid bare. The hills directly north of Storm 
Canon show excellent outcrops of the propylite, which is here made up of 
hornblende, frequently fresh and well preserved, built (as is the rule in 
the propylites) of thin, staff-like microlites impregnated with small, black 
grains. Zirkel found the hornblende in places considerably decomposed, 
resulting in calcite, epidote, and viridite. The feldspars are often fresh and 
quite large, a majority bearing distinct triclinic striations, with a few pale, 
small orthoclases. Brown mica occurs sparingly, and besides hornblende 
the rock contains an inferior amount of yellowish-green augite. 

In Toyabe Range, near Boone Creek, the prominent ridge of quartzite 
is enclosed on the east and west by rhyolitic rocks, the latter breaking 
through upturned Miocene strata. Near the junction-line, where the 
quartzite passes under the rhyolite, are two rather obscure outcrops of 


normal hornblende-propylite. he surface is much decomposed, and there 


PROPYLITES AND QUARTZ-PROPYLITES. HD 


is very little of the hard material that can be observed; yet the chips with 
which the surface is covered are characteristically of the normal green 
hornblendic propylite. It decomposes in soft, earthy, olive-colored slopes, 
which are overlaid by both rhyolite and basalt. The outcrops are too 
obscure and too limited to be specially instructive. 

An interesting locality of propylite is that at Kaspar’s Pass, north of 
Hot Springs Station, at the southwestern end of Montezuma Range. The 
termination of the Montezuma is a deeply scored mass of rhyolite, over- 
flowed by basalts which chiefly cover the southern slope of the hills. 
The base of the range, from the northern edge around as far as White 
Plains, is completely surrounded by outcrops of Truckee Miocene, which 
are inclined toward the range until in the neighborhood of the rhyolites 
they are thrown into irregular dips, having been burst through and over- 
flowed by the rhyolitic bodies. These Miocene strata are more or less 
covered by accumulations of Quaternary. Through Quaternary, imme- 
diately in the vicinity of Kaspar’s Pass, comes to the surface a body 
of propylite which occupies the whole of the Pass from the rhyolitic 
foot-hills on the east to an oval body of basalt which forms the western 
side of the valley. The basalts on the west, and the Montezuma rhyolites, 
clearly overlie the propylite; and although the relation between the Mio- 
cene and the propylite is obscured by Quaternary, all the appearances tend 
to the belief that the Miocene beds abut unconformably against a preéxist- 
ing body of propylite. This is rendered very probable by the material of 
the Miocenes, which is here altogether of the upper or trachytic tuffs. The 
surface of the propylite is much weathered, resulting in soft olive earth, with 
predominating propylitic chips. It consists of hornblende and triclinic feld- 
spars, more or less altered, and epidote, a pseudomorphous product after 
hornblende. The microscope reveals, as Professor Zirkel describes,* all the 
pseudomorphic changes between hornblende and epidote. 

The lower Truckee Canon, from about two miles above Wadsworth, 
for six miles up the canon, has its bottom largely occupied by propylite. It 
is entirely unconnected with any stratified rocks, and no clew is offered to 
the orographical disturbances related to its ejection. It occupies only the 


* United States Geological Exploration of the Fortieth Parallel, Volume VI., page 114. 


554 SYSTEMATIC GEOLOGY. 


low land at the bottom of the valley, and is covered upon either side by 
more recent trachytes. A mass of diorite upon the river bank about four 
miles above Wadsworth is the only older rock in the neighborhood, being 
a hard, fresh boss of well preserved rock, around which the soft, earthy 
propylite has flowed. The propylite is of a dull olive-green, and is 
much decomposed, the feldspars reduced to soft, kaolinic masses, of which 
even the crystalline forms are chiefly lost. The groundmass is reduced 
to an almost amorphous paste, and there is a good deal of partially 
decomposed brown mica. The rock is full of dark green waxy spots, which, 
in favorable instances, were seen to retain the distinct form of augite. It 
is clearly an augite-propylite, similar to that discovered by Richthofen at 
Silver Mountain, which is here in the last stages of decomposition. It is of 
interest in this connection because this is the only locality of augite-propylite 
within the Fortieth Parallel area. It is overflowed by peculiar augitic tra- 
chytes, by light rhyolites, and finally by basalt. 

A few miles north of Truckee Canon, at Berkshire Cafion, a gorge 
eroded down the eastern flank of Virginia Range, occurs a fine association 
of voleanie rocks which have burst out in immediate contact with a 
body of older melaphyre. The propylite forms the earliest of the volcanic 
series, and occurs in a body of purple rock lying along the eastern flank 
of the lofty mass of melaphyre. It is invaded by quartz-propylite and by 
andesites, and is overflowed at the northern end by trachyte, which, 
in its turn, is covered by rhyolite, and that is succeeded by basalt. It is a 
rather earthy, compact propylite, composed of triclinic feldspar and ereenish- 
purple hornblende, with a little magnetite, apatite, and occasional grains 
of mica. The outcrops are very limited, and for the most part covered 
with soil and overwhelmed by later ejections. 

In Steamboat Valley, a little south of the west end of Map V., there is 
in the low lands a considerable development of hornblendic propylite, in 
which decomposition has reached an advanced stage. The staff-like 
growth of the hornblende is traceable in some of the better preserved crys- 
tals, the nature of the groundmass is totally obscured, and the feldspars are 
altogether kaolinie. 


At all the localities heretofore mentioned, the propylite is displayed 


PROPYLITES AND QUARTZ-PROPYLITES. 5D 


sufficiently for identification, and in nearly all cases for determining its age 
relatively to the surrounding eruptive rocks; but for minute study of the 
rock itself the occurrences are usually too disintegrated and altered for the 
collection of really specific types. ‘They are all very restricted localities, 
and all occur at rather low altitudes, and offer none of the bold characteristic 
outcrops which mark the high parts of Virginia Range. So far as I have 
seen, from Pyramid Lake southward to its junction with the Sierra Nevada, 
Virginia Range shows at frequent intervals enormous fields of propylitic 
rock. South of Carson River it recurs at intervals for many miles, and in 
the Washoe mining district is displayed on a scale which is unsurpassed any- 
where in the United States Cordilleras. In Volume III, ‘ Mining Indus- 
try,” page 25 et seq., a detailed account is given of its mode of occurrence. 
Again, in Volume VI, ‘“ Microscopical Petrography,” page 110 e¢ seq, 
Professor Zirkel has rehearsed the prominent features of that classic 
propylite locality. 

Without repeating here what was said there, it seems necessary to re- 
capitulate the broader facts of its mode of ejection and the leading petro- 
graphical characteristics of the rock. Prior to the propylite period, Vir- 
ginia Range consisted of upturned sedimentary rocks—slates, limestones, 
nodular schists, and quartzites—whose original disturbance was connected 
with intrusions of true granite. Through these had outburst great dioritic 
masses whose hard summits had withstood erosion and formed culmi- 
nating points of the range. The propylitic ejections took place from a series 
of fissures running longitudinally with the range and extending from 
summit to base on both sides. The diorites of the Mount Davidson ridge 
are cut by broad propylitic dikes, and similar lines of fracture may be 
traced north and south along the summit of the range for many miles. 
Down the south and east sides of the ridge the propylitic rocks poured 
quite to Carson Plain, and upon the west to the level ground of Steamboat 
Valley. Only the highest portions of the diorite summits were lifted above 
the enormous floods of propylite which poured out from these longitudinal 
fissures. The eruption was not continuous, but clearly intermittent, as is 
shown by the manner in which later propylite dikes cut through the heavy 
flows of the earlier ejections. 


556 SYSTEMATIC GEOLOGY. 


There is no evidence of the propylite having flowed in the sense of an 
andesite or a basalt. It never extended in thin sheets, but was evidently 
ejected in a viscous condition, accompanied (if we may judge from the 
present aspect of its areas) by enormous amounts of water, and de- 
veloped a sluggish flow down the rather steep slopes of the range. The 
first eruptions were of normal crystalline propylite, uniformly porphyritic, 
and almost wholly of olive-green colors. The second ejection, which had 
its centres of eruption north and south of Mount Davidson, was of a coarse, 
propylitic breccia, which contained fragments as large as a foot in diameter, 
enclosed in an ordinary propylitic matrix, the breccias varying from green 
to purple. The third period of eruption was in the form of narrow 
dikes without any considerable outflow. They cut the main body of the 
propylites and the overlying breccias in the north-and-south lines, the dikes 
varying from six to thirty feet in thickness. Near Geiger Grade, north and 
west of Virginia City, may be seen the relics of these hard, crystalline 
dikes, which have withstood erosion better than the soft breccia, or even 
than the main porphyritic eruption. In consequence, they stand up in bold 
remnants of sheets which once formed the dike, towering thirty or forty 
feet above the surface. 

In immediate contact with the diorite, some of the early ejections were 
of an exceedingly fine, compact texture, developing a fissile structure re- 
sembling some fine hornblendic slates. Above the level of Comstock 
Lode the propylite is altogether unaltered, but east of it the whole pro- 
pylitie region is more or less wackenitic from solfataric action. At the 
lower levels, near Carson Valley, the ejections, as has been heretofore 
mentioned, were sublacustrine, resulting in rudely stratified, muddy tuffs. 
These extend about 600 or 700 feet above the present level of the river. 
The belt of middle altitudes below the level of the Comstock Lode is an 
area of earthy soft rock, frequently decomposed into white, yellow, and red 
clays, in which the original structure of the propylite is only indicated by 
soft, kaolinic white spots, the relics of the feldspars. 

The eruptions through which the upper Crown Point and Ophir ravines 
are eroded offer the best examples of fresh, unaltered rock. Specimens col- 


lected from these two localities are seen to be composed of a light greenish 


PROPYLITES AND QUARTZ-PROPYLITES. 557 


or olive groundmass, which is made up of fine triclinic feldspar and the 
fibrous dust of green hornblende. In this characteristic groundmass are 
plagioclases of pale gray, white, and greenish-gray colors. Like the feldspar 
of the groundmass, these crystals are throughout impregnated by a dust of 
feldspar microlites. The hornblende, which is of green and olive colors, is 
seen even with the loupe to be made up of individualized hornblendic fibres. 
This observation was first made by Richthofen, and was subsequently sus- 
tained under rigid microscopical analysis by Zirkel. <A characteristic of 
the rock is the tendency of this fibrous hornblende to become altered into 
epidote, a very large amount of the Washoe propylite showing the apple- 
green color due to this pseudomorph. Besides these characteristic minerals, 
there is always a little orthoclase, and not infrequent augite crystals. The 
microscope also reveals apatite and magnetite. In the normal propylites 
there is often a little accidental quartz, but never a well established transi- 
tion between the hornblende-propylite and the true quartz-propylite. 

Of all volcanic rocks, propylite is most readily decomposed; the pecul- 
iar character of the fibrous hornblende offers easy avenues for mineral 
solutions or gases. And this is true not only of the complex hornblende 
crystals which are made up of staff-like microlites, but also of the feldspar 
of the groundmass and of the larger feldspar crystals themselves, which 
are permeated in every direction by the fibrous hornblende. As a conse- 
quence, nearly all the propylite observed by us is decomposed. The entire 
absence of glassy base is one of the features which render the field aspect 
of the rock different from the family of andesites. There is never any of 
that subtle reflection of light which is one of the characteristic appearances 
of the andesitic surfaces. The propylites, on the contrary, are even duller 
and deader than the older diorites. From the latter they may be easily 
distinguished in the field by the behavior of the superabundant horn- 
blende, which in propylite always presents a dull, velvety appearance. 


Quartz-Propyiites.—That part of Cortez Range which lies south of 
Humboldt River describes a curve, with its convexity to the southeast. It 
is composed of older masses of Carboniferous and granitic rocks, associated 
with diorite, upon which are piled up complicated occurrences of volcanic 


558 SYSTEMATIC GEOLOGY. 


rocks. The earliest of these is a small mass of propylite already described 
in Wagon Canon. After this come the quartz-propylites, the most im- 
portant mass of which forms the summit of Cortez Peak, next to Tenabo 
the highest point of the range. The granite body that forms the northern 
foot-hills south of Granite Creek, gives way in the higher part of the range 
to a bold mass of quartz-propylite which has a general oblong form, being 
three or four miles across the range and extending northeasterly on the 
strike of the ridge about eight miles, forming a rude parallelogram. Upon 
the south and west the quartz-propylites overflow a heavy body of quartzite, 
which has been referred to the Weber period of the Carboniferous. West- 
ward they overlap the old granites, and to the east and north they are 
capped by the more recent members of the volcanic series. The exposure 
is such that we have no distinct clew to the rocks through which the quartz- 
propylite came to the surface; but from the structure and appearance of 
the granite it seems most probable that it came through a broad fissure in 
the granite itself. At all events, it occupies a position high in the centre 
of the range, its present highest point reaching an altitude of 8,383 feet. 
To the north the slope of the ridge passes underneath a body of rhyolites 
which occupy the mountain summit for about eight miles in a northeasterly 
direction. 

At Papoose Peak the underlying quartz-propylites again come to the 
surface and continue northward for about eight miles, where they pass be- 
neath a flow of dacite. There is little doubt that the masses of Papoose 
and Cortez peaks form one body, whose continuity is only masked by the 
overlying rhyolites. Here, as at Washoe, they come to the surface not far 
from the earlier eruptions of diorite. As to the actual date of the eruption, 
the locality of Cortez Peak affords no clew whatever. When it is re- 
membered that in the whole Great Basin, which, with the Sierra Nevada, 
proves to be the great voleanie field of the Cordilleras, there are only a few 
obscure and isolated outcrops of Eocene, and that the characteristic expo- 
sures of Miocene are confined to a few localities in western Nevada, it is 
not surprising that the data for determining the actual ages of the earlier 
volcanic products are so few and imperfect. 

Toward the northwest the quartz-propylites of Cortez Peak offer rough, 


PROPYLITES AND QUARTZ-PROPYLITES. 559 


craggy terrace-slopes, exposing a great deal of solid rock, which displays 
exceedingly broken, irregular forms, the fracture being always rounded. 
There are certain broad, horizontal divisions which seem to represent 
heavy, single ejection-beds, varying from ten to fifty feet in thickness, as 
if an exceedingly viscous body had poured out with extreme slowness and 
become rigid upon the steep front. The abrupt slopes do not seem to be 
altogether the result of erosion, but partly at least of the rude piling up of 
these thick, viscous beds, the result of single throes of eruption. The gen- 
eral color of the natural surface of the rock is a soft gray, pinkish, and 
salmon-color, which is locally varied by green and olive hornblende. The 
groundmass consists of clear, dark plagioclase, more or less altered fibrous 
hornblende, and purely microscopic quartz, the latter containing fluid inclu- 
sions with (in some instances) included cubes of salt. The hornblende, as 
described by Zirkel (Vol. VL, page 119), is clearly made up of prismatic 
staffs characteristic of the propylite family, which distinguish it from the 
andesites and dacites. The microscope also showed the usual titanites. 
An incomplete analysis of this rock appears in the table of analyses, No. 
VII. The larger feldspars are all dull and slightly kaolinized, but under 
the microscope show feeble traces of former triclinic striation. 

The northern continuation of this quartz-propylite body, in the neigh- 
borhood of Wagon Camon, is an almost precisely similar rock, the micro- 
scope showing the same fluid inclusions in the quartz, and, in addition to 
the minerals of the Cortez Peak rock, a few laminz of brown mica, which, 
curiously enough, contain thin layers of pellucid calcite. 

The Cortez Peak mass, besides the overlying rhyolites at the north, 
is further masked by a broad field of basalt which skirts it along the east, 
the sequence of eruptive rocks here being granite, diorite, quartz-propylite, 
rhyolite, and basalt. 

At Papoose Peak the quartz-propylite is overlaid by a narrow band of 
normal trachyte, which in its turn is overlaid by a line of rhyolitic hills that 
separate it from the plain. Along its eastern side the body of quartz-pro- 
pylite, from Wagon Caton to Papoose Peak, is further overlaid by dacite. 
The quartz-propylite has the appearance of having been erupted in an almost 
solid condition, showing no tendency to spread out into thin sheets. The 


560 SYSTEMATIC GEOLOGY. 


lower exposures contain no biotites, and both hornblende and plagioclase 
closely resemble those of Cortez Peak. Biotite seems to be characteristic 
of the last ejections. A similar sequence will be noticed later in the chap- 
ter at Berkshire Canon. It has always appeared to be the rule among 
trachytic rocks, so far as our observations go, that the biotite-bearing sani- 
din variety immediately succeeds the gray variety, which carries a large 
amount of hornblende and plagioclase, and which really seems to be an 
intermediate rock between the true trachytes and true andesites. Here, 
again, in the quartz-propylites, is repeated the same condition, a mica- 
bearing rock succeeding a hornblende-bearing rock. Among the curiosi- 
ties of decomposition is the fact that the hornblende is far more changed 
than the feldspar, while at Cortez Peak the reverse is true. The actual 
proportion of biotite in the latest outburst at Papoose Peak is really very 
small, but it is a very conspicuous mineral on account of its large, irregular 
flakes, which seem to have a parallel arrangement. With these minor 
differences the rocks of Papoose and Cortez Creeks are the same. 

Between the stations of Iron Point and Golconda, Humboldt River 
cuts a narrow, rather sharp cation diagonally across a chain of hills which 
diverge from Havallah Range in the neighborhood of Cumberland and 
extend northeasterly. In the region of Cumberland these hills are formed 
of granite, which a few miles to the north is overlaid by sedimentary beds 
that from their lithological character and stratigraphical peculiarities have 
been referred to the Trias, although no fossil remains were found. South 
of the river these rocks develop a well defined synclinal, in the axis of 
which is a limited body of quartz-propylite that possesses the trend of the 
axis, north-northeast, extending for about two and a half miles, its transverse 
breadth being very slight, not over one fourth to one half of a mile. On 
the little map at the close of this chapter it is erroneously colored as pro- 
pylite. In a yellowish-gray groundmass appear large, clear quartzes, and 
dull, opaque, white feldspars; the latter, like the groundmass, having suf- 
fered considerable decomposition. As throughout the propylite family, the 
hornblende is made up of acicular hairs which also permeate the ground- 
mass and the feldspars, greatly facilitating their decomposition. Among the 
curious things developed by the microscope is carbonate of lime incrusting 


*sisAyeur 
jo Jaqum yy | 


125 


130 | 


132 


133 


TABLE OF CHEMICAL ANALYSES. VIIIL—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. 
PROPYLITES AND QUARTZ-PROPYLITES. 


Propylites. 
2 FE ‘ Oxygen ratio of—| FI 2 
22 Locality. Analyst. Si | At | Fe | Fe | Mn | Ca | Mg eNa | K Li '= |) Total apes ha | cog 
gs & Te | Sh Le 
A =) Oo & 
125 | Washoe (Virginia City) - - - - |W. G. Mixter - | 58-66] 17-90] . .| qx] . .| 5.87] 2.03] 2.07) 3:19 | 6.53 | 100.36 2.65 4.46 | 8.34 | 31.28 | 0.409 
31.28 8.34 eee 0.91 Brent 1.67 0.81 0.53 0.54 | 8 che a 355 | 9.71 31.28 | 0.423 
; ! 
126 | Connection between Truckee and | R. W. Woodward / 60.33] 19-74] 0.70] 2.50] tr. B:73)\ed-Orle-361|| 1-62]|\ anne naar o 3:13] ro0.12] 2.6, 2.7 | 4.60) 9.40) 32.17 | 0.447 
7 Montezuma ranges. 32.17 9-19 0.21 0.55 ee 1.06 1.60 4.12 0.27 eo yr. ed anni oan A ae 
127 | Storm Canon, Fish Creek Moun- SS 60.55) 17-43] 3:07] 2-54] tr. 3:87| 2.65] 3-39) 4-46) tr. |CO?trace.| 2.23] roo.19 2.6 4:35 | 9.04 | 32.29 | o.4n4 
tains. 32-29 B.12 0.92 0.56 clk 1.10 |~ 1.06 0.87 0.76 Be 0 Fgiow tea as ee oat are | Paaee ee 
ws sr “ a 60.58] 17.52| 2.77| 2.53) tr. 3-78| 2.76] 3.30] 4-46] tr. |CO* trace.| 2-25) 99.95 ata 4:35 ) 8.99 | 32.30 | 0.413 
32.30. | | 8136.| 0.83; | 0156) || «9. ||| «x.08)) |) xsxomIMED. 85) |||) (00760) | ae eee Slr fas a Beeler | 2 |) qt 
128 | Cross Spur, below Grave-Yard, |W. G. Mixter - | Go.82] 17.54] - -| 5-42] - -| 5.65] 1-76) 3-71) 1-41] . - || CO? r4t 2.31| 100.39] 2-66, 2.68 | 4.71 | 8x7 mall 0.307 
Washoe. 32-43 8.17 Or" 1.20 ae 1.61 0,70 0.96 0.24 qo it Beit: oD ROE: eer) 3.5t | 9.07 | 32.43 | 0.415 
129 | Virginia Range, Sheep Corral Cafion| Prof. Wiedermann| 64-62] 11.70] . . | 8.39| - -| 8.96) 1-18] 3.13] 1-95] - - | PO* trace.) 1.02] 100.95 mo 6.03 | 5.45 | 34-46 | 0.333 
aed |e ls 6 aloe eres | Ox | Goal) Oeil o 5 Ree eas a: oes Sues 4.17! 8.24 | 3446 | 0.360 
> ; 7 
Quartz-Propylites. 
130 | Hills east of Havallah Mountains - |W. Kormann - | 66.34| 14-80] 4.07| . . . .| 2.99] 0.92 5.16 3:19| - - | CO? 7.03 2.31| 100.81 ia 3.90 | 6.90 | 35.38 | 0.305 
35-38 6.90 1.22 are) ne 0.85 0.37 3-33 0.54 ee fiat NS ae . ts os 3.09 | 8.12! 35.38 | 0.317 
. : | 
131 | Hill west of American Flat, Washoe} W. G. Mixter - | 68.44] 14-86] . -| 3.80 . . 1.90 5.08] . - | CO? 0.94 2.26| 100.50) 2.63, 2.67 | 307 | 6.92 | 36.50] 0.273 
36.50 6:92 ||| ‘0/84. |. sees 0.54 0.86 eae ae het Fie 2.23 | 8.19 | 36.50 | 0.285 bi, 
132 | Mullen’s Gap, Virginia Range - - | R. W. Woodward | 68.46) 16.85 1.43 tr. 2.92 3:98| tr. | CO? 0.59 I.45| 100.03] 2-38, 2-44 | 305 | 7:85 |36.5r | 0/298 
* 36.51 7.85 = we 0.32 aks 0.83 0.67 agro hee ae evo ee oa 2.73 | 8.33 | 36.51 | 0.303 
133| Foot-hills, Virginia Range, Sheep “ Wea) AA] go ll egja oo |] Ore (@2]) 3 o 518). 0 1.79 | 100.04 
Corral Cation. 30/68) |) -oxegalel|( oe sul natosasen” senile tomas 1.02 thes aa 
| 
{ 


PROPYLITES AND QUARTZ-PROPYLITES. 561 


in a crystalline dust the more decomposed feldspars, and there are the 
usual fluid inclusions in the quartzes. These, however, are varied by the 
occurrence of double inclusions of liquid carbonic acid and water. The 
rock has the usual field habit of all the quartz-propylites—a very roughly 
fractured exterior, dull, lustreless surface, and the peculiar half earthy look 
produced by the partial decomposition of the groundmass. This little iso- 
lated body of quartz-propylite is not immediately associated with any other 
voleanic rocks. Two miles to the east, at the base of the hills, there is a 
slight development of basalt; and west of Rocky Creek, in the neighbor- 


hood of Golconda, there are powerful ejections of rhyolite. 

The following table, No. VIIL., gives the constitution of several of the 
most important occurrences of propylite and quartz-propylite. 

36 K 


SECTLON it. 
ANDESITES AND DACITES. 


Andesitic rocks have a somewhat wider distribution than propylites, 
but within the Fortieth Parallel limits they hardly cover a greater topo- 
eraphical area. Together with their related dacites (the quartziferous spe- 
cies), they are scattered in limited exposures from Cedar Mountains, in the 
Great Salt Lake Desert, to California. In general they occupy subordinate 
topographical positions, and with the exception of a few points in the Sierra 
Nevada, beyond the western limits of our work, they appear altogether 
as massive eruptions. Andesitic volcanos probably contemporaneous with 
the massive eruptions of Nevada and Utah, are placed at intervals along 
the axial line of the Sierra Nevada and Cascade Range, both hornblende 
and augite-andesite occurring there as true volcanos. The relics of an 
enormous extinct crater at Lassen’s Peak mark an andesitic volcano of the 
first order. Much of the crater wall, however, has been engulfed, and its 
place is occupied by modern trachytic and rhyolitic cones. The andesites 
of the Fortieth Parallel are never extensive outbursts, or rather the present 
exposures are never extensive. How far they may be covered up by suc- 
ceeding outflows can not be determined. The most eastern exposure is in 
the Traverse Mountains, a small group of hills which extends westward 


from the base of the Wahsatch, connecting that range with the Oquirrh. 


Hornpienpe-ANDESITE.—On the divide between Gosiute Valley and 
that of Deep Creek, among outcrops of rhyolite which are separated 
from each other by accumulations of Quaternary, rises an isolated hill of 
andesite. The exterior surfaces which have been subjected to weathering 
are of a pale-grayish mauve, almost a lavender-color; but the fresh fracture 
shows a dark-brownish, compact rock of felsitic habit, with a remarkably 
homogeneous, half glassy matrix, including small white crystals of plagio- 
clase, occasional brown micas, and the normal andesitie hornblende, together 
with a few rounded grains of quartz. The hornblende shows the exterior 


562 


ANDESITES AND DACITES. 565 


modification described by Zirkel as one of the constant microscopic pecu- 
liarities of andesitic hornblende. The quartz, which occurs in detached 
cracked granules, does not appear to be a constituent of the groundmass, 
but occurs as an accidental accessory constituent, after the manner of cer- 
tain quartziferous trachytes. The rock could not be at all classed as a 
dacite, in spite of the presence of these accessory quartzes. 

South of Palisade Canon, facing the Cluro Hills, along the western 
side of Cortez Range, is a rather obscure, dark, even-grained andesite, evi- 
dently later than the porphyry and syenite which come in contact with it 
on the west, and probably earlier than the dacite which lies east of it, though 
their relative ages have not been satisfactorily made out. Although it con- 
tains but little hornblende, the absence of augite probably refers it to the 
hornblende-andesite. 

Cortez Range is one of the most broken up and geologically compli- 
cated of any in the Great Basin. It exhibits andesites from the region of 
Tuscarora at intervals as far south as Papoose Peak, some distance south of 
Humboldt River. Breaking through and overlying the propylite of the 
Tuscarora region, is a limited body of andesite, which is overlaid on the 
west by rhyolites. It is a dark, compact rock, rather reddish on the weath- 
ered surface, and shows to the unaided eye small brilliant plagioclases and 
black hornblende crystals in a dark greenish-gray groundmass. Under 
the microscope, Zirkel found the hornblende green, and more or less fibrous. 
Its geological habit also inclines toward the propylites, which it somewhat 
resembles as to the character of the hornblende. 

At Carlin Peaks, in Cortez Range, latitude 40° 45’, the summits of 
the Lower Coal Measure limestone are flanked on the west by a small body 
of andesite, which is surrounded on the north, west, and south by subse- 
quent rhyolite. The andesite is piled up in a mass, rising about 1,200 feet 
above the surrounding rhyolites. It is a dark-gray, compact rock, very 
rich in hornblende, although carrying a good deal of yellowish-brown augite 
and a little apatite. Besides the predominating plagioclases, there are 
some schistiform sanidins. A few miles to the south, where the Emigrant 
Road crosses Cortez Range, is a second body of andesite, overlaid by 
trachytes on the south, but surrounded on the east, west, and north by 


564 SYSTEMATIC GEOLOGY. 


rhyolite. It is unimportant geologically, and possesses no petrographical 
differences from the rock mentioned at Carlin Peaks. 

Above the head of Clan Alpine Canon the summits of Augusta Range 
are formed of andesite masses, the crests of an earlier topography, which 
have remained lifted above the later floods of rhyolite, or perhaps which 
erosion has recently exhumed from the overlying acidic rocks. The ande- 
sites have a rudely columnar structure, and are made up of plagioclase and 
hornblende, the latter showing the characteristic black boundary, and the 
groundmass is distinctly made up of microlitic particles of the two minerals. 
The long hornblende prisms are noticeable for a rude parallel arrangement. 
A few miles north, the region around Crescent Peak and the head of Au- 
gusta Caton shows a considerable field of andesite, which has broken 
through and overflowed the Mesozoic limestone, in turn overlaid by 
trachytes and rhyolites in the order mentioned. The groundmass of this 
rock has a prevailingly earthy character, owing to the varying decomposi- 
tion of the hornblende. 

Zirkel calls attention to the interesting manner in which the hornblende 
crystals of this locality, viewed with the microscope, are seen to have been 
ruptured and the particles moved away from one another. In some cases 
nearly all the fragments of the crystal remain embedded in the ground- 
mass within the field of view, when the eye readily reconstructs the form 
of the original crystal. At other times detached fragments not traceable 
to the parent crystal are seen. There are certain very distinct instances of 
fluidal motion, the chips of a crystal being thrown into wavy lines like the 
figures of marbled paper. 

The little group of Kamma Mountains, lying west of Montezuma 
Range, in latitude 40° 45’, forms an isolated series of hills rising about 
2,000 feet above the desert. The southern portion of the group and a 
few detached outliers in the lowland south of the main group are made 
up of hornblende-andesites. The outcrops toward the summits of the 
mountains form jagged, prominent peaks, with considerable exposures of 
bare rocks. Farther down the slopes there seems to be a distinctly bedded 
structure with an inclination of the sheets to the east. Still farther, the low 
hills are mostly covered by recent detritus and afford no very characteristic 


ANDESITES AND DACOITES. 565 


exposures. This rock is a true hornblende-andesite, the groundmass con- 
sisting chiefly of plagioclase containing a high proportion of black opacite 
grains. All the andesites of this region south of Lander Spring have a 
more or less trachytoid habit, the weathered surfaces having almost the 
roughness of trachyte, quite that of the dacites. There is a noticeable 
amount of sanidin in the composition of the rock, which doubtless accounts 
for the peculiar roughness of the texture. 

The little group of andesitic hills a few miles north of Kamma Range, 
at Indian Springs, show a somewhat similar superficial roughness, and upon 
closer examination the rock, although a true andesite, is seen to contain an 
unusual proportion of large crystals of sanidin, together with decomposed 
hornblendes, in a compact close-grained, greenish-gray groundmass. There 
is nothing in the geological occurrence of the andesites of this region to 
distinguish them specially. They are the oldest eruptive rocks of the 
neighborhood, with the exception of the small body of middle-age diorites. 
The relation between the detached small bodies of andesite lying south of 
the main Kamma Mountains and the slightly inclined Miocene beds does 
not appear, the superficial Quaternary preventing any true solution of their 
position. Taking the outflows of these andesites as a whole, they seem to 
be related to the western margin of the great body of Jurassic slates which 
form the western flank of the northern part of Montezuma Range. Where 
those westerly dipping slates finally disappear beneath the low desert coun- 
try, is doubtless the mountain fracture which gave vent to the andesites. 

From the valley of Glen Dale eastward, Virginia Range is cut directly 
across by the cation of Truckee River. At the western or upper entrance 
of the canon the hills on either side rise from 1,500 to 1,800 feet above the 
level of the river. Those to the south are formed of thickly bedded ande- 
sites and andesitic breccias of prevailing grayish-brown, reddish-brown, and 
chocolate-brown colors. There cannot be less than a thickness of 1,200 or 
1,400 feet of accumulated beds, showing every varicty of texture, from a 
rough, loose, trachytic, porous mass to an extremely compact, highly erys- 
talline body resembling the best preserved porphyritic andesites of Washoe. 
The beds all incline toward Truckee Canon. The lowermost members 


of the series are of compact reddish-gray and olive-gray flows, with a gray 


566 SYSTEMATIC GEOLOGY. 


microcrystalline groundmass, in which hornblende and triclinic feldspar 
and a few large, conspicuous crystals of augite are seen. Over these, form- 
ing by far the greater portion of the series for a thickness of not less than 
1,600 feet, are reddish-brown, highly cellular, almost scoriaceous andesites, 
containing both hornblende and augite, with a decided predominance of 
the latter, the whole overlaid by a thick series of andesitic breccias, of 
which most of the fragments contain augite to the exclusion of hornblende. 
Much of the breccia is decomposed, leaving earthy masses of which the 
hornblende crystals are decayed past recognition. Although distinctly a 
massive eruption, the physical character of these andesites partakes much 
more of the andesitic lavas of a true voleano. They were evidently ejec- 
tions from a deep fissure, coming to the surface near the summit of the 
range, and pouring down one over the other, exactly as upon the flanks of 
a true voleano; and the loose, scoriaceous habit of a large part of the mid- 
dle series closely corresponds with the andesitic material thrown out from 
the ancient crater of Lassen’s Peak. With this exception, all the andesites 
of the Fortieth Parallel are decidedly compact, having the habit of ordinary 
massive eruptions. It is not at all impossible that the inclined beds repre- 
sent the fragmentary remains of some old andesitic volcano, most of whose 
body is now covered by the later eruptive rocks of the neighborhood. 

The narrow andesite body which lies along the eastern flank of the 
melaphyres of Berkshire Canon in Virginia Range has an east-and-west 
breadth of not more than a quarter of a mile, but extends about six miles 
north-and-south. Like the neighboring propylite, it is wonderfully trachytic 
in appearance. The groundmass is a grayish-brown feldspathic body with 
but little brown hornblende distributed through it. The large crystals and 
fragments of crystals of hornblende, however, which lie porphyritically 
embedded in it, are arranged with a certain degree of parallelism. This 
rock most closely resembles those earlier trachytes of the Washoe region 
which underlie the sanidin varieties, and which by their high proportion 
of black hornblende and plagioclase closely approach the andesites The 
middle ground between the andesites and trachytes is occupied by a gray 
or grayish-brown rock, carrying a predominance of hornblende over biotite, 


with plagioclase and sanidin in about equal proportion. When the texture 


ANDESITES AND DACITES. 567 


of the groundmass is rendered trachytic by a high proportion of horn- 
blende, the habitus of the rock inclines obviously to the trachyte family. 
But when the groundmass is composed predominantly of feldspars, and of 
those feldspars the plagioclases equal or exceed the orthoclase, the habit 
of the rock becomes truly andesitic. Out of this middle region, therefore, 
between the two species, when, as is often the case, one cannot decide 
upon the predominance of included orthoclase and plagioclase, the habitus 
of the groundmass gives a pretty sure indication of the general group it 
belongs to. 


Dacitr.—The eastern half of Cortez Range, from four or five miles 
south of Papoose Peak nearly up to Humboldt Canon, a distance of four- 
teen or fifteen miles, is composed mainly of a continuous field of dacite, 
which seems to prolong the line of eruption determined by the quartz 
propylite of Cortez and Papoose peaks. As an eruption, it shows no 
tendency to form sheets or extend itself laterally from the region of fissure. 
On the contrary, it behaves like granite or the least fluid of the trachytes. 
It is essentially a massive eruption, and north of Wagon Canon shows a 
thickness of at least 1,200 or 1,500 feet. Like the andesites, its surface is 
very easily decomposed, the prevailing character of the rock is rather 
earthy, and the colors vary from purple to chocolate and brown, the later 
eruptions north of Wagon Canon growing pale and approaching grays and 
olives. At the southern end the mass is overlaid by high piles of rhyo- 
lite, and the eastern base for many miles, as the map shows, is overlaid by 
basalt. Along its eastern line it quite distinctly overlaps the quartz- 
propylite, and is therefore later. North of Wagon Canon the basalts give 
way, and the Pliocene strata of Pine Valley come directly in non-con- 
formable contact, abutting against the slopes of dacite. The field habit of 
this dacite is decidedly more propylitic than andesitic. There is a lack of 
the resinous lustre and the easy, glassy fracture of hornblendic and augitic 
andesite. In the field and in hand specimens we were often unable to dis- 
tinguish between it and quartz-propylite. But in the case of this outburst 
it might readily be mistaken for the neighboring quartz-propylite. The 


chocolate-colored and purple groundmass encloses peculiar white kaolinic 


568 SYSTEMATIC GEOLOGY. 


erystals of feldspar, which in the least decomposed portions show under 
the microscope triclinic striation, and numerous black and_ glittering 
quartzes. The rock is really a dacitic breccia, since the groundmass con- 
tains numerous fragments, both angular and sub-rounded, of a similar pur- 
ple dacite, whose only difference from the enclosing material is, that the 
kaolinized crystals of plagioclase are much smaller than those secreted in 
the matrix. The microscope shows that the kaolinized feldspars are pene- 
trated by fine crevices carrying chalcedony. In various directions through 
the rock are late fissure-lines, which may be traced by a rusty ferruginous 
color penetrating the purple groundmass a short distance on either side 
of the crack, resulting no doubt from the decomposition of the hornblende. 
Those hardly perceptible traces of motion which indicate to the eye whether 
the viscous movement of the body has been in horizontal beds or simple 
vertical planes, show in this instance that it was vertical. 

North of Wagon Canon, where dacite forms the crest of the ridge, the 
rock is decidedly less brecciated than to the south. It is purplish-green, 
and is very noticeable for large, opaque, triclinic feldspars. The horn- 
blende is fresh and brownish, and there are a few flakes of biotite in the 
microfelsitic groundmass. Throughout this whole mass the quartz crystals 
are all very dark, and but rarely visible macroscopically. ‘The microscope 
reveals their abundant presence everywhere, and it also shows that the 
glass base is of the gray type. 

At Shoshone Peak, the culminating point of Shoshone Range, in the 
midst of a broad area composed of Carboniferous quartzites, dacite forms 
a small, insular mass, its overflow making the highest point of the range at 
Shoshone Peak, 9,760 feet above sea-level. This outburst has occurred on 
the line of a flexure in the quartzites which still earlier was marked by a 
small eruption of diorite in a cation north of Shoshone Peak. It is at once 
the most elevated and most interesting outburst of this rock within the 
limits of our survey. Petrographically it is of importance as including 
the largest quartz grains of any Fortieth-Parallel dacite, many reaching 
the diameter of an eighth and some a quarter of an inch. The general 
color of the rock shades from purple to green. Not a little of it in the 


lower exposures, indicating the earlier stages of the eruption, is rudely 


ANDESITES AND DACITES. 569 


brecciated. Between the dacite breccia and the compact, uniform rock, 
there is every transition, some hand specimens showing a single included 
angular fragment not larger than a pea. The most important structural 
characteristics of this exposure are the powerful vertical jointing-planes 
which in some places approach the regularity of a columnar structure. 
The groundmass is often so coarse that the particles of triclinic feldspar 
and fresh hornblende may be seen by using the loupe, and occasionally 
with the unaided eye. ‘Toward the east the cliffs of dacite are eroded down 
sharply in canons, modified, if not determined, by glacial action. The 
bold, rocky fronts of the spurs and the flanks of the cations offer admirable 
exposures of the rock, the slight accumulation of soil and the absence of 
forest trees combining to make it the most imposing exposure of dacite in 
the Fortieth Parallel area. In weathering, the groundmass, feldspars, and 
hornblendes wear down pretty evenly, leaving the erystals of quartz, which 
are often dihexahedral forms, standing out along the surface. The geo- 
logical aspect in the field of this and of the other dacites often resembles 
certain metamorphic quartz-porphyroids. The surface is exceedingly rough, 
the fracture more like that of propylite, the low proportion of the glass base 
rendering the lustre dull and very different from the resinous brightness of 
the quartzless andesites. 

Virginia Range, so justly noted for its varied and extensive display of 
voleanic species and varieties, exhibits typical dacites at three points within 
the limits of our Exploration. Abreast of the southern end of Pyramid 
Lake the range is severed by the deep pass of Mullen’s Gap. The hills both 
north and south of this depression, ascending to considerable heights, 
are composed of a gray dacite, which weathers in rough, rounded forms, 
and is conspicuous by a very dull surface, resembling the propylites. It 
varies from gray through several olive-greers to purple, and in all hand 
specimens shows more or less distinctly striated plagioclase and macroscopic 
quartz. The latter, as described by Zirkel in Volume VI, page 139, carries 
distinct fluid inclusions. The hornblende also is of the true andesite-dacite 
type, and not the polysynthetic propylite variety. Of all the dacites, in 
external habitus this most closely resembles the propylite type, and it is 


by mistake colored upon our geological map as quartz-propylite, close 


D770 SYSTEMATIC GEOLOGY. 


examination having been made too late for a change. The rounded or 
rudely crystalline grains of quartz are brilliantly vitreous, and are fissured 
in every direction by innumerable cracks, closely resembling the rhyolitic 
quartzes, with the exception that the latter almost never contain fluid 
inclusions. For analysis of this, see table of analyses No. IX. 

Throughout this northern portion of Virginia Range there are no ante- 
Tertiary rocks, except the limited development of melaphyres in the region 
of Berkshire Canon. The relation of the overflow of Tertiary ejecta to the 
earlier range cannot here be made out. Farther to the south, Archean, 
Mesozoic, and middle-age eruptive rocks form the distinct body and core 
of the range, over which the Tertiary species have poured. In the northern 
portion now under consideration, although the heights are maintained up to 
8,000 and 9,000 feet, the entire range is masked by enormous floods of 
trachyte and basalt. It is only in the lower portion of the hills, however, 
that the earlier Tertiary eruptive species come to the surface. Along the 
eastern flank, at Berkshire Canon and for about four miles northward 
and the same distance southward, the andesites and propylites which lie 
along the eastern base of the melaphyres are broken through by repeated 
flows of dacite, the latter extending southward to the mouth of Sheep 
Corral Canon and forming a distinet foot-hill region, noticeable for its 
purple and green colors. The mode of weathering of this rock resem- 
bles that of the older diorites. It appears in low, rounded hills, exposing 
considerable stretches of smooth, rocky surfaces not covered by earth or 
recent débris. ‘The harder quartzes frequently stand out prominently upon 
the surface. 

Very considerable portions of this outflow are of a fine-grained, purple 
groundmass, with no included crystals recognizable to the unaided eye. 
From this fine microcrystalline condition it passes into a more coarsely 
crystalline groundmass, in which triclinic feldspar and more or less brown 
hornblende are easily detected. Through these earlier purple dacites 
have broken large volumes of dacitie breccia, which carries a ereat 
deal of dark, bronzy-brown magnesian mica. The percentage of free 
quartz erystals is also higher than in the earlier outflow. Last of all, and 


closing the dacite period in this neighborhood, came a pale, apple-green 


ANDESITES AND DACITES. 571 


dacite, richest of all in quartz. It is interesting for the decomposition of 
the feldspars and their conversion into carbonate of lime and kaolin. As 
in the dacites of Shoshone Peak, which these often closely resemble, the 
quartz grains are frequently dihexahedral. The anomalous position of a 
crystal of quartz containing fluid inclusions in a glass-imbued groundmass 
is difficult to explain, unless it may be an ingredient of an older rock, which 
has escaped fusion. 


Avaire-AnpEsItE.—The limestone body of Cedar Mountains, a de- 
tached range southwest of Salt Lake, is accompanied by outbursts of volcanic 
rock. The oldest of these is at a remarkable bend in the range, near its 
southern extremity, a little north of latitude 40° 15’. The limestones, which 
have stretched southward from the northern portion of the range for about 
thirty miles, suddenly bend off to a southeast strike. Directly at the inter- 
section of these two strikes, where a very great strain must have occurred 
in connection with the flexure of the strata, there is an outburst of andesite 
which occupies the angle of the range. The desert Quaternary deposits 
rise high upon its flanks, and probably cover a considerable portion of the 
andesite flows. Four or five miles to the southwest, a small isolated butte 
of andesite rises out of the Quaternary, and is evidently separated from 
the main mass by a thin blanket of loose soil. The external appearance 
of these andesites is quite like that of basalt. Its structure is that of 
thin sheets, which often display a rude, columnar jointing. The reddish 
weathered surfaces also resemble some of the thinly bedded basalts. Upon 
fracture, the rock is seen to contain considerable pale-gray glass, the larger 
crystalline secretions being plagioclase, augite, and a few hornblendes, to- 
gether with a little brown biotite. Augite predominates over hornblende. 

An interesting group of andesites occurs on the northeast base of the 
Wachoe Mountains, longitude 114° 30’. The hills consist of a granitic 
core against which rest considerable bodies of limestone belonging to the 
Lower Coal Measure series. Diorites and felsite-porphyries are connected 
with the disturbances of the middle age, and andesites and rhyolites form 
the features of Tertiary eruptive activity. The andesites are all seen along 


the northeast base of the group; and with the exception of a small, isolated 


572 SYSTEMATIC GEOLOGY. 


hill south of Last Chance Spring, are all overlaid by rhyolite. The ande- 
sites at the mouth of Spring Canon, as exposed where the rhyolites have 
been eroded away, together with the butte south of Last Chance Spring, 
exhibit a dark gray, rather compact groundmass, which the microscope 
shows to possess a pale gray glassy base. Besides plagioclase and augite, 
which are the predominating crystalline secretions, there are a few horn- 
blendes and a little sanidin. The eruption of these andesites is of the 
usual massive type, spread out in rather thin sheets. Although the out- 
flows are arranged on a northwesterly trend, yet the northernmost out- 
crops, north of Melrose Mountain, are of a different petrographical nature. 
The groundmass is dark, steely gray, the crystalline secretions being a 
little orthoclase, fine, brilliant crystals of plagioclase, predominating biotite, 
and afew broken, acicular hornblendes. It is classed by Zirkel as the mica 
equivalent of hornblende-andesite. Externally, with the exception of the 
evident mica, the rock has the same geological habit and aspect as the 
Spring Canon outcrops. Like that, it is surrounded and in great part coy- 
ered by rhyolite, and presents the ordinary characteristic dull-red surfaces 
of weathered andesite. Under the hammer it breaks with sharp fracture 
and shows the resinous lustre of semi-vitreous rocks. 

The River Range lying north of the Humboldt, in middle Nevada, is 
suddenly cut off a few miles north of Penn Canon. The range, which has 
been a well defined quartzite ridge for fifty miles, suddenly plunges down 
beneath a broad flood of rhyolitic and andesitie rocks. There is no doubt 
that this break in its continuity is due to a fault, and that the andesite has 
come up in the fracture-region. 

The North Fork of Humboldt River flows through the horizontal Pli- 
ocene of Bone Valley, and then cuts a sharp gorge, to which Mr. Emmons 
gave the name of Egyptian Canon, through a field of andesite For about 
eight miles along the canon, by four or five miles in width, is exposed a body 
of andesite which is overlaid by the horizontal Humboldt Pliocene strata 
of Bone Valley on the north and similar beds at the lower end of Egyptian 
Cation. East and west it is overlaid by fields of rhyolite. The physical 
habitus of this rock, in a broader sense, is strongly like that of basalt. It is 


composed of tabular layers, which along the walls of Egyptian Caton show 


ANDESITES AND DACITES. Dili 


a rude columnar structure, in which the columns are cylindroids rather than 
prisms. There is also a tendency to split into plates perpendicular to the 
axis of the cylinders. It is to those two sets of fissurings that the peculiar 
architectural aspect of the region is due—an effect resembling ruined columns 
of an Egyptian temple. Under the hammer the rock has the usual flinty 
fracture, totally different from the rough, ragged fracture of basalt. A speci- 
men from the lower end of the cafton shows a groundmass entirely made up 
of microlites and grains of plagioclase and augite, free from olivine; the 
only larger crystalline secretions being small, pellucid plagioclases. Near 
the upper end of the canon is a very remarkable variety of the rock, having 
a dark, brownish-gray groundmass which carries sanidin crystals half an 
inch in length, and a few cracked and rounded granules of quartz, altogether 
similar to those in the augite-andesites of Cedar Mountain; the main ingre- 
dients, however, being plagioclase and augite. Like the specimens col- 
lected at the lower end of the camion, it contains no olivine. The micro- 
scope shows considerable quantities of apatite. Between the basalts, which 
want olivine, and the augite-andesites, which are totally free from horn- 
blende, it is not easy to determine, either by microscopic analyses or by 
examination of hand specimens. The question of devitrification of the 
glassy base is not in itself sufficient. ground for a distinction between the 
two species. At the time Professor Zirkel’s examinations were made, the 
field-notes were not written out, and he was not informed as to the condition 
in the field. The rock is earlier than the Pliocene and surrounding rhyo- 
lites, and its habits are altogether those of andesite. For this reason we 
have decided to class it among the andesites. 

A few miles south of Tuscarora is found a small body of augite-ande- 
site, entirely surrounded by rhyolites. It is of no particular importance, 
except for the extremely fine development of augites and the fact that the 
plagioclases, which reach the size of a hazel-nut, are extraordinarily rich in 
inclusions of yellow glass. 

The valley of Susan Creek is occupied by horizontal Pliocenes which 
continue southward from the valley of the North Fork of the Humboldt, 
forming a narrow strip between the rhyolite hills of Seetoya Range. On 
the east side of Susan Creek Valley, about abreast of Maggie Peak, between 


DTA SYSTEMATIC GEOLOGY. 


the creek and River Range, is a small body of augite-andesite coming to 
the surface under trachytes and rhyolites. The weathered surfaces have 
a pale greenish-gray color, but the fresh fracture is very dark brown, 
almost black, and possesses the brilliant resinous lustre characteristic of 
the family of andesites or of the most glassy basalts. Crystals of sanidin 
and plagioclase can be detected in the fine-grained groundmass, as well as 
clear, well shaped augites, the latter standing out prominently on the weath- 
ered surfaces. As usual, the rock contains no olivine. 

Palisade Canon is eroded through a body of trachyte, to be hereafter 
described. A prominent ravine, entering the canon from the north, lays 
bare a body of andesitic rock of very peculiar constitution. It is a dark 
eray rock, having the characteristic fracture and surface of andesite, but 
the very fine-grained groundmass contains augite, plagioclase, biotite, and 


angular grains of quartz which, together with apatites, are found embedded 


in some of the larger feldspars. The association of augite and quartz 
renders the rock particularly interesting. 

On the gentle eastern slope of Cortez Range, south of Wagon Canon, 
a long, narrow exposure of augite-andesite comes to the surface, enclosed 
on all sides by dacite, which strongly resembles it in color, texture, and 
general geological habit. The two rocks disintegrate with abowt equal 
ease, and the earlier (for so it seems to be) andesite is probably a portion 
of a prior outburst, from which erosion has removed the covering of dacite. 
It is indeed possible that the andesite has broken up as a dike through the 
dacite, as data for their relative ages are wanting. The color of the mass 
varies from brown to purple, very much of the surface being covered with 
minute chips of the solid portions. The fresh fracture shows the usual 
resinous lustre due to gray glass, which constitutes the base of the rock. 
The groundmass is much discolored and decomposed, passing from the color 
of chocolate to a rusty iron-red, and at times pale yellow and brown. In 
it are plagioclases, more or less kaolinized, showing traces of zonal struct- 
ure, yellowish augites, and occasional but rare flakes of biotite. 

In the valley of Reese River, directly north of the little town of Ja- 
cobsville, is an isolated mass of hills connected with the southern part of 


Shoshone Range by a flow of rhyolite. The little group known as Jacob’s 


ANDESITES AND DACITES. 575 


Promontory is made up largely of quartzites, considered to belong to the 
Weber period, which here have a very dark, ferruginous color. Through 
these, at the northern and southern foot-hills of the group, long anterior to 
the period of the trachytes and rhyolites, have burst out masses of dark 
augite-andesite with a distinctly columnar structure and a light-gray weath- 
ered surface. When broken, it has a sharp, conchoidal fracture and a dis- 
tinetly resinous lustre, owing to the high proportion of glass base. The 
groundmass is composed of plagioclase and olive-colored augite. Besides 
these minerals, there is a little sanidin and a few irregular, broken crystals 
of hornblende, the latter having the appearance of a foreign ingredient. 
Under the microscope, the plagioclases are noticed by Zirkel as containing 
well defined inclusions of brown glass with thick bubbles, the augites also 
containing large glass inclusions which themselves contain augite microlites. 
This locality is of special interest, since here the augitic andesite is dis- 
tinctly overlaid by basalt, the greater relative antiquity of the former rock 
being thus clearly demonstrated. 

In the southern portion of the Augusta Mountains, south of Shoshone 
Pass, in the region of Crescent Peak, where the stratified Mesozoic lime- 
stones are overpoured by heavy masses of hornblende-andesite, the latter 
have been broken through and in turn overflowed by a highly glassy augite- 
andesite, resembling in external features and in geological habit the occur- 
rence at Jacob’s Promontory. At the head of Augusta Canon, and over 
the ridge to the north, the augite-andesites superposed upon the horn- 
blende variety are seen in distinct columnar structure, the individual prisms 
varying from a few inches to a foot or two in diameter, and commonly dis- 
playing a fairly regular pentagonal section. The exterior surface of the 
blocks, to the depth of about a tenth of an inch, shows a light grayish- 
green color, the result of the alteration of the groundmass. Directly be- 
neath this altered layer is a dull-reddish, rusty zone, and then the dark, 
fresh, resinous, glassy material of the main mass. A few miles farther 
north, on the western side of the range, at Antimony Canon, similar augite- 
andesites appear, which have broken through and overlaid brecciated 
hornblende-andesite, the latter overlying, as in the Crescent Peak region, 
masses of older hornblende-porphyry. In both of these latter localities the 


576 SYSTEMATIC GEOLOGY. 


augite-andesite is of distinctly later origin than the hornblende-andesite, a 
fact which is elsewhere repeated, and to which the field observed by us 
offers no exception. It is also extremely important to note that the augite- 
andesites of the Augusta Cafion region are overlaid by the trachytes that 
form the extreme heights of the range. At Jacob’s Promontory we saw 
that the augite-andesite was of earlier age than the basalt; here it is seen 
to be earlier than the trachytes. In other words, it belongs manifestly to 
the andesitic period, and since it clearly followed the hornblende-andesites, 
it may safely be held to close the andesite period. The rock, then, should 
be considered a true dependent of the andesite family, and not of the basalt 
family, to which its petrological features far more closely ally it. The im- 
portance of this region cannot therefore be over-estimated, as will be seen 
when we come to treat the natural classification of volcanic rocks. 

In a side ravine of Truckee Canon, three miles north of the main river, 
occurs a limited outcrop of dark rock resembling basalt in appearance and 
mode of occurrence. It is surrounded by rhyolites. Under the microscope 
appear both orthoclase and plagioclase in about equal proportions, green 
augites, and abundant olivine, the latter surrounded by an encircling band 
of green augite prisms arranged tangentially. It is classed by Professor 
Zirkel as an augite-andesite, the silica equivalent being far too high for the 
true basalts, to which its large tenure of olivine would naturally ally it. 
The silica equivalent is doubtless to be accounted for by the abundant pres- 
ence of a highly acid glass which fills all the spaces between the crystals 
of the groundmass. 

Directly south of Wadsworth are three detached hills of black rock, 
the northern one of the true basalt, the two farther south of augite-andesite. 
The groundmass is a dense aggregation of minute plagioclase, magnetite, 
and augite-microlites, in which are embedded sanidins and plagioclases in 
about equal proportion. Although augite is distinctly in excess, there is 
yet considerable light-brown hornblende with the characteristic black border 
of the andesite-hornblendes. Olivine is wanting. 

In the rolling hills west of Steamboat Valley, Nevada, somewhat north 
of the group of springs, are augitic andesites composed of a very light 
grayish-green groundmass, in which are well defined green augites up to 


TABLE OF CHEMICAL ANALYSES. IX.-UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. 
ANDESITES AND DACITES. 


Andesites. 
a a ¢ a : Oxygen ratio of— & 3 
2 = Locality. Analyst. Si Al Fe Fe Mn | Ca | Mg | Na K Li 3 Total. | Specific |] 20,2 
55 5 gravity. |p | |e |Fs 
rae D R Si |# 5 
| a oa 
| 
134 Ridge northeast of American Flat, | W. G. Mixter - | 58.33| 18.17] - -| 6.03] . .| 6.19] 240] 3.20| 3.02] - . | CO? 2.85 | 0.76) 99.95] 2-72, 2.76] 545) 846 31.10 | 44s 
Washoe. PE |) aS | a o roel lt eee x77 | 0196) || vote | ost | . ames ae oe SO 4.06 | 10.47 | 3.10 | 0.467 
135 | Silver Terrace, Washoe - - - - ct =|) Gopal) Ghee! o ol} (NE) a o|) Hel] Boel] sgh) sees) o 3 gH 0 2.80] 100,02 2.6 5:30} 8.48 }3r.5s8 | 0.436 
31.58 GO) a o oPa80i|| acne 1.57 x16 | 0.85 | 0.24 % ees iit ha ae 3.82 | 10.71 | 31.58 | 0.460 
136 | Main Ridge, above Three Knobs, | R. W. Woodward) 60.71] 16.00) 2.09} 3-87) - -| 5:17] 3:07) 2-74 3-78 tr. | CO? r.o1 1.48 99-92] 2.6, 2.5 | 492] 8.08) 52.97] o.4or 
Cedar Mountains. 32-37 7-45 0.63 0.86 od 1.48 1.23 O.7t 0.04 5. pis o> 0 oa aes rage SPA eeeen| oes||\ be 
137 | First hill north of Gold Hill Peak, |W. Kormann - | 61-12] 11-61] 11-64] - «| - + | 4.33 0:61) 3785] 3:52) - « goa 3 4:35 || 101-03 ghaid 5:39] 5.4t| 32.59] 0.33% 
Washoe. 32.59 5.41 Bey || oo oh a8 1.23 | 0124 || worgg) | 0.60 |. foc so ee ae: oe 3.061|| B.90\||42.59\| 0.466 
138 | North Pass, Cortez Mountains - - | R. W. Woodward} 61.64] 17-44) 0.82) 3-99] tr. 5-86| 3:05] 3:45] m-r5| tr. bo 0 2.64] 100.04] 2.6, 2.5 | 485) 8.37) 32.87) 0.402 
32.87 8.13 aay || Es lo 1.67 x22 | 0.8) | o19 | . « oe feat ee eae oft Nees Wercee: lee 
139 | North bank of Palisade Canon - -|Reinhard- - - | 62-71) 12.10/ 14-79) - -| = = 8.34] 1-31] O73) TI5] ~« - oo 4 a of] iennng Rae 6.24) 5.64) 33.44) 0.355 
33-44 5.64 4-43 : : 2,38 0.52 6.19 9.19 doo 300 8 0.0 mo 0 a 4 3-28 | 10.07 | 33.44] 9.399 
(~4D 8 6.16 6 
140 | Wachoe Mountains - - - - -|R.W. Woodward | 67.81) 17.60 2.11 tr. 3.15] 1-08] 2:97} 3:85) - - a0: 1.57| 100.14] 2.5, 2.6 | 322] 8120] 3646) 031 
} 36.16 8.20 0.70 0.47 a0 0.90 0.43 0.77 0.65 9.6 og 3 G9 qe 8g F/G 2.75 | 8.99} 36.16] 0.322 
ADA ; 8.42 36 
« “ ES a Se 67.63| 18.08 2.17 tr. 3:16) 1-14 P87) 3:80) «= a6 "0 1.49] 100.40 Pare 3.22 | 8.42] 36.07) 0.322 
36.07 | 8.42 Peewee ool] Gall cus | «ARI oo POP. vi fen ooo ee 2.74| 9:14] 36.07] 0.329 
Dacites. 
i i ity, Wa ii so : 5 a z a ont et 1.3 2.0 3.6 aoe setae We 2.1 101.9 was 3.00 | 8.34| 36.95] 0.307 
141 | Hills above American City, Washoe | C. Coiincler 69:3, | 1) hs an | ee |: ae 4 We Roce sion | evalltacieel Retare 
| 
25 . * H . . 2.90] 7.53] 37-41 | 9.276 
142 | Shoshone Peak, Shoshone Range - | R. W. Woodward| 70.17 14-53) 2:54) 3-74) ' | 2:29) 0:95 325) 3:35) ut 0 ey) |e SOTERA es fas 
at). Gor | ene | oise)| «|| oc6ng|| eee | °-57 oy ee bo 
‘ | 37-46) 0. 
“ “ « bs « 70.25) 14.90] 2-57 1.76 tr. 2.39, 0.83} 3:24} 3-22 tr. te deo 1.51 100.67 te 2 au 17 u : 9.279 
|| Gs 0.77 0.39 0.68 0-33 | 0-8 HE 2 Re ie? 
3 = | 


ANDESITES AND DACITES. SHITE 


the size of a pea, feldspars, both orthoclase and plagioclase, of equal dimen- 
sions, a little sharply crystallized magnetite, and some apatite. Not atrace 
of hornblende was observed in this rock. The external appearance and 
habitus of this occurrence are distinctly andesitic, the bedded flows resem- 
bling those of the hornblende-andesites which overlie the propylites near 
Virginia City. 

The following table, No. IX., gives analyses of several of the most 
important andesites and dacites, 

37 K 


SEC ito Nite 
TRACHYTES. 


We have seen that the propylites, quartz-propylites, andesites, and 
dacites occur very sparingly over the Fortieth Parallel field, and are alto- 
gether confined to the region west of Wahsatch Range, with their greatest 
concentration at the extreme western limits of our work. The trachytes 
which we are now about to consider, have a somewhat peculiar distribu- 
tion. They occur chiefly in four well defined groups: 

1. That of the Rocky Mountains, which consists of two main out- 
bursts, one constituting the divide between North and Middle parks, the 
other in the Elk Head Mountains, directly west of Park Range. This forms 
an entirely detached group, with no trachytes over an interval of 4° of 
longitude westward. 

2. The next group appears in the region of Wahsatch Range and Salt 
Lake. North of the railway, at longitude 109° and 109° 20’, several little 
dots have the characteristic trachyte color on the small map at the end of 
this chapter. But these are so colored to avoid the expense of another 
stone, and are really leucitie rocks, not to be confounded with the trachytes. 
The Wahsatch trachyte group consists of several outbursts, the most prom- 
inent of which lies between the western end of Uinta Range and Clay- 
ton’s Peak in the Wahsatch. The line of fissure through which this ejec- 
tion has taken place is a great fault, slightly diagonal to the axis of the 
Wahsatch, and its trend is defined by a line of trachytic outcrops shown 
on East Cation Creek. At the western base of the Wahsatch, in the Trav- 
erse Mountains, directly opposite the broad field of trachyte east of Clay- 
ton’s Peak, are two important bodies, one occupying the Traverse Moun- 
tains and the other the slopes of the eastern spurs of the Oquirrh. 

3. Passing over an unimportant mass in the Tucubits Mountains in 
northeastern Nevada, the next considerable trachytic region is that of Pinon 


and Cortez ranges and their continuations to the north. Here, from the 
578 


TRACHYTES. 579 


southern limit of our map as far north as Nannie’s Peak in Seetoya Range, 
are exposures of considerable masses of sanidin-trachyte. 

4. The last noteworthy locality is that of Virginia and Lake ranges in 
the vicinity of Pyramid Lake, where large portions of the mountain bodies 
are composed of trachytes. 

It is curious to observe that these four important groups are separated 
from each other by intervals of 4° of longitude. 

The group in the Rocky Mountains is directly contiguous to important 
folds of Archzean rocks, a region which has been the theatre of orograph- 
ical movements in very carly times. The group of Wahsatch trachytes 
accompanies one of the most important geological centres of the whole 
Cordilleras, where the deepest stratified rocks are exposed, and where 
immense dislocations of the crust and excessive erosions have taken place. 
It is a region of exceptional geological grandeur and activity. Passing 
westward to the group of Cortez and Pinon ranges, we come again to a 
region of unusual geological conditions. It is here that the older Devo- 
nian and Silurian rocks are brought up from great depths to the surface, 
and evidence of remarkable faults in Tertiary times is not wanting. Again, 
as regards Virginia Range, it may be said that it is the most important of the 
meridional ridges which branch off from the northwest trend of the Sierra 
Nevada. Itis a range in which perhaps a greater volcanic activity was 
maintained throughout the whole period of time covered by the Tertiary 
eruptions than in any other east of the Sierra Nevada. 


During the period of the deposition of the Cretaceous, North and 
Middle parks were unquestionably one basin. The orographical movement 
which accompanied the close of the Cretaceous epoch threw up an east-and- 
west ridge, dividing the basin into two parts. The character of the disturb- 
ance of this ridge was very complicated, being something more than a mere 
anticlinal. Either then or later, there was a sudden fracturing uplift, accom- 
panied by outpourings of great volumes of a peculiar rock, having certain 
affinities on the one hand with the family of trachytes, and on the other 
with the older granite-porphyries. The rock in question occupies a large 
portion of the surface of the ridge which culminates in Parkview Peak, a 


580 SYSTEMATIC GEOLOGY. 


point rising more than 12,000 feet above sea-level. The exposures of the 
Cretaceous rocks indicate mere dislocated fragments wedged in between the 
enveloping flood of eruptive rocks, the blocks themselves being subse- 
quently cut through by east-and-west dikes of similar volcanic material. 
Aside from the supposed Pliocene beds of the Park, evidently a very recent 
lacustrine series, there is no means of positively determining the age of this 
eruption. From its intimate relations with the broken, dislocated fragments 
of Cretaceous strata, it is evident that its eruption was contemporaneous 
with the fracturing and breaking up of the Cretaceous ridge. It is indeed 
possible that this took place during the Tertiary period, at the time of the 
general trachytic eruptions which we have seen reason to place within the 
Miocene. But it seems quite possible that this great disturbance of the 
Cretaceous was coeval with the formation of other similar Cretaceous up- 
lifts, which in the Green River Basin are clearly seen to have preceded the 
earliest Eocene deposits. 

Rocks similar to the trachytes of Parkview Peak are found along the 
Elk Head Mountains, and the identical species has been brought to light 
by the researches of G. K. Gilbert in the Henry Mountains. In all three 
of these places, facts necessary to fix the actual date are wanting. In each 
case this rock accompanies peculiar local disturbances of Cretaceous rocks. 
Its affinities with the older granite-porphyries, together with its peculiar 
relations to the Cretaceous, suggest that it is a special group long antedat- 
ing the other trachytes, and to be assigned to the very dawn of the Eocene 
period. The east-and-west dikes which cut the blocks of Cretaceous 
strata, and the main fields of eruptive rock, have withstood atmospheric 
agencies remarkably well, and rise above the sandstone like stone walls. 

East of Parkview Peak, near Middle Park Trail, are some isolated 
hills and cones which Professor Zirkel has described as granite-porphyries. 
These and the rocks from Parkview Peak are petrographically similar, 
although the field habit is like that of true trachytes. The yellowish-gray 
groundmass consists of orthoclase, quartz, and a little hornblende; it is 
extremely fine-grained and nearly homogeneous. The most remarkable 
lithological point is the occurrence of orthoclases in perfect individuals, 
presenting faces such as heretofore have only been found in middle-age 


TRACHYTES. 581 


granite-porphyries of Europe. Besides these orthoclases are a few small 
plagioclases, hornblende, apatite, titanite, magnetite, and pyrite, the latter 
having a brilliant, brassy color. From similar rocks at Steves’ Ridge these 
are distinguished by the microscopic behavior of the hornblende, which 
gives the green sections characteristic of the older rocks, by the fact that 
the quartz contains fluid inclusions, but none of glass, and by the presence 
of pyrite and titanite; whereas the similar trachytes of Steves’ Ridge con- 
tain ample glass inclusions in the quartz, and neither titanite nor pyrite, 
and the hornblendes have the usual brown sections. At the same time, the 
physical likeness of the rocks is wonderfully complete. The modes of 
oceurrence are similar, both are involved in dislocated Cretaceous strata, and 
neither can be positively referred to a later disturbance than that which 
marked the close of the Cretaceous. Further, the Henry Mountain rocks, 
which according to the observations of Gilbert, cannot be earlier than the 
end of the Cretaceous, have also apatite, titanite, and fluid inclusions in the 
quartz, besides both green and brown sections of hornblende. xamina- 
tion of several of these specimens shows the uniform presence of highly 
modified orthoclase, which in some cases has the glassy habit of sanidin 
and in others resembles that of granite and granite-porphyry. 

From a geological point of view it seems to me most correct to refer 
this rock to a new group, for which I propose the name of trach ytoid-porphyry, 
the group representing, both in geological date and in physical habits, the 
transition between the porphyries, whose occurrence in the Cordilleras has 
never been known to be later than the close of the Jura, and the Tertiary 
voleanic series. It is true that one extreme of the group is indistinguishable 
from the earlier granite-porphyries except by the trachytic mode of eruption, 
while the other extreme falls within the petrographical limits of true tra- 
chytes. The writer has examined specimens where the quartzes contained 
fluid inclusions with moving bubble, while the hornblendes contained 
ample glass particles. 

There is a decidedly sudden change between the Parkview rocks and 
the summit south of Ada Spring, the former occurring as cones, sharp 
peaks, and long, irregular dikes, while farther west the region is a broad 


trachytic plateau with escarped faces. The rock south of Ada Spring is 


582 SYSTEMATIC GEOLOGY. 


unmistakably a fine-grained, dark-gray trachyte, the groundmass consisting 
of sanidin, augite, hornblende, biotite, and apatite ; the microscope showing 
the augite to predominate greatly over the hornblende. The main plateau 
shows everywhere dark-grayish and brownish-gray rocks of the same char- 
acter, in which augite always predominates over hornblende or biotite, and 
sanidin over the small brilliant crystals of plagioclase. The ordinary 
rough trachytic habit is well displayed, and the rock in every way contrasts 
with the trachytoid porphyries of Parkview. The augitic rock is later, 
and doubtless belongs to the regular Miocene trachyte period. 

The Archean mass of Park Range suffers an important change of trend 
about the latitude of 41°, the neighborhood of Davis Peak being the region 
of deflection. Within this angle and west of the range are the Elk Head 
Mountains, a group whose position doubtless depended upon the Archean 
angle. The eruptive rocks of this group consist of trachytes and basalts. 
The former occur close to the Archean rocks, from Hantz Peak to Camel 
Peak, and thence extend southward from Steves’ Ridge and Whitehead Peak 
in a broad field about thirty-five miles long. The highest summit is that 
of Hantz Peak, which reaches 10,906 feet, while the other three peaks 
mentioned are all over 9,000 feet, and Whitehead reaches 10,317. The 
greatest east-and-west expansion is a stretch of twelve or fourteen miles from 
Crescent Peak to Hantz Peak. The trachytic eruptions come to the surface 
through a preéxisting uplift of Cretaceous rocks of the Fox Hill and Colo- 
rado groups. As a whole, these rocks are all sanidin-trachytes. One type 
is made up of a rough, porous, crystalline groundmass, in which are large, 
highly modified sanidins, similar to those already mentioned at Parkview 
Peak. A prominent variety of the true trachytes of this region contains in 
the characteristic groundmass a great many brilliantly clear, rounded gran- 
ules of free quartz, which are peculiarly cracked and riven, not unlike some 
of the quartzes of rhyolite. All the quartz is confined to these large macro- 
scopical grains, the microscope showing none whatever in the groundmass. 
It is essentially an accessory mineral, like the tridymite of other tra- 
chytes. It frequently contains glass inclusions. Besides large sanidins and 
quartzes, the rock contains hornblende, a little mica, a comparatively high 
proportion of augite, and, in a few instances, olivine. The outcrops are 


TRACOYTES. 583 


generally in rounded dome-like hills and sharp cones, offering a great con- 
trast with the more level plateaus of basalt to the west. It is probable that 
the high ragged cone of Hantz Peak formed one of the centres of eruption. 

Crescent Peak with its southeast spur and Skelligs Ridge are inter- 
esting trachytie dikes rising above the neighboring Cretaceous strata, 
having from their more resisting nature suffered far less erosion than the 
enclosing sandstones. South of Whitehead Peak the trachytic ridge has a 
broad gentle slope, extending out to the edge of the valley of Yampa River. 
The rock of Whitehead Peak is a peculiar grayish-drab trachyte, having 
an unusual tendency to split into laminee half an inch to an inch thick. In 
the purplish-gray, fine-grained groundmass are enclosed crystals of sani- 
din, hornblende, and augite, with large cracked globules of pellucid quartz, 
a few bronze micas, and numerous reddish-brown spots of serpentinized 
olivine. The large sanidin crystals, which frequently measure an inch or 
more in diameter, show a tendency to zonal decomposition. 

The Sugar Loaf, an isolated trachytic mountain west of Elk River, is 
composed of a rock of massive habit, containing in a porous gray ground- 
mass large, highly developed sanidin, hornblende, and black biotite, but 
none of the quartz which is characteristic of the main trachytie body to the 
north and west. Upon a spur extending northwest from Steves’ Ridge, not 
far from Steves’ Fork, is a very characteristic quartziferous trachyte, in 
which the sanidin crystals are often more than an inch long, associated in 
the groundmass with biotite and hornblende. Some of the earthy, soft 
varieties from this locality have an easily decomposed groundmass, from 
which the large, highly modified sanidin crystals may be readily separated. 
The surface of the rock here, like that upon Whitehead Peak, is peculiarly 
pitted where cracked granules of quartz have been weathered out. On the 
eastern spurs of Steves’ Ridge, which project toward Park Range, occur 
further quartziferous trachytes containing considerable olivine, together 
with a free sprinkling of brownish mica. The trachyte of Crescent Peak 
is mineralogically like that of Whitehead, with the same peculiar habit of 
splitting into amine of an inch to an inch and a half in thickness. 

Skelligs Ridge is one of the most interesting developments of trachyte 


in this curious region. The body of the dike, which is from twenty to fifty 


584 SYSTEMATIC GEOLOGY. 


feet thick, rises out of the soft, grassy slopes of eroded Cretaceous sand- 
stone to a height of 150 feet, and extends in a northwest direction, with 
a single considerable break, for five or six miles. The walls are nearly 
vertical, and the rock is composed of rude columns arranged horizontally. 
The weathered surfaces have a peculiar, pitted appearance from the drop- 
ping out of the rounded granules of quartz Mineralogically it is like the 
rock of Crescent Peak, and is doubtless a continuation of the same erup- 
tion. The western spur of Crescent Peak is peculiar from the absence of 
all crystallized secretions from the groundmass. It is an exceedingly com- 
pact, fine-grained, homogeneous mass, and the only included bodies are 
clear, brilliant granules of fractured quartz, which are often stained brown 
by the decomposition of the iron of the surrounding mass. 

Camel Peak, which is the northernmost point of this great trachytic 
field, rises like a wedge for 2,500 feet above the valley. The groundmass 
of the rock is homogeneous, very fine-grained, and in general bluish- 
gray, containing besides the quartz grains only a few flakes of black mice 
with occasional hornblendes and augites, the microscope showing that the 
augites predominate. Upon the freshly fractured surfaces the globules of 
quartz stand out with a pale, earthy green coating closely resembling the 
delessite amygdules of basalt. Numbers of specimens collected between 
Steves’ Ridge and Camel Peak are of this same type—dark, compact rocks, 
containing quartz and augite, with more or less olivine; a few specimens 
showing considerable biotite, a high proportion of augite, and but little 
olivine. Some forms approximate very closely to basalt, and it seems 
as if the whole northern region represented a sort of transition between 
the true trachyte period and that of the basalts, the genuine basalts break- 
ing out later, 

Hantz Peak, the dominating point of the region, shows about 300 feet 
below its summit the edges of sedimentary beds, chiefly of sandstones, 
which are highly altered and in some cases distinctly vitrified. Above these 
are the mauve-colored trachytes which are seen to split easily into laminze 
that have generally a very felsitic appearance, the groundmass containing 
the usual rounded quartz, white, rather decomposed feldspar, a little black 


mica, and hornblende. The very summit of the rock, however, is made up 


TRACHYTES. 085 


of a white trachyte having some of the characteristics of rhyolite. But it 
is considered only a local deviation from the general trachytic type. The 
very sharp, isolated crest has been frequently struck by lightning, and is 
grooved out in radiating trenches by the force of the bolts. 

On Slater’s Fork, near its junction with Little Snake River, is seen a 
small outcrop of trachyte which the valley-erosion has exposed. It is a 
narrow body extending about a mile and a half east-and-west, passing 
under the basalts at its eastern termination. It is exceedingly compact, 
and the groundmass is cryptocrystalline, the eye detecting only flakes of 
brown biotite. The microscope shows predominating sanidin, plagioclase, 
abundant augite, and a few olivines, but neither quartz nor hornblende. 
There is, however, a little distinct nepheline. 

The trachytes of this eastern Rocky Mountain province may be summed 
up under two distinct types: that which appears upon Steves’ Ridge, and 
which in the crystalline form of its unusually large sanidins so closely re- 
sembles the highly modified orthoclase of granite-porphyries; and the re- 
markable family of quartziferous augite-trachytes, which are nowhere so 
well developed in the Fortieth Parallel area as here. Their peculiarity is, 
that the groundmass contains no microscopical quartz, while large globules, 
up to one eighth of an inch in diameter, remarkably split and cracked, are 
very prominent among the crystalline secretions. Olivine is of not infre- 
quent occurrence, and augite always predominates over biotite and horn- 
blende. Plagioclase is invariably present, but in smaller amounts than the 
sanidin. It seems to be a thorough mingling of the constituent minerals 
of basalt and rhyolite; there being present the sanidin, biotite, quartz, and 
occasional hornblende, characteristic of rhyolite; and the augite, triclinic 
feldspar, olivine, and magnetite of basalt. 


In the northern angle between Green River and Bitter Creek, rising 
out of the plains of Green River Eocene strata, is a single isolated body 
of augite-trachyte, presenting abruptly escarped faces on all sides. The 
soft and easily eroded material around its base shows no traces of local 
disturbance. The recent washing and erosion of the Tertiary soil would 


naturally cover up any slight local disturbances, and it is therefore uncer- 


586 SYSTEMATIC GEOLOGY. 


tain whether this isolated mass of trachyte has burst up in situ, or whether 
it is the sole surviving fragment of a flow. It is uncommon in the geology 
of the Cordilleras for jets of eruptive rock to burst up through horizontal 
strata without any orographical disturbance. At the same time it is 
common to find the fragments of a flow which have escaped general ero- 
sion; and in the case of Pilot Butte it is impossible to assert positively 
what its deeper relations may be. In composition it is an augite-trachyte, 
not unlike those of the Elk Head region. 


Next to the Elk Head trachytes, the most extensive exposure within 
our area is that which lies along the eastern base of the Wahsatch, 
separating it from Uinta Range. A reference to geological Map IIL, on 
which the relations of the trachyte to the surrounding sedimentary rocks 
may be clearly seen, will show at a glance that the main line of the trachyte 
eruption has a north-and-south trend, that it breaks through the de- 
pressed region between Uinta and Wahsatch ranges, and in passing north- 
ward cuts a diagonal into the heart of Wahsatch Range. The most im- 
portant body is that which overlies the Cretaceous and Eocene Tertiary 
in the neighborhood of Wanship, and extends thence southeastward for 
thirty-five miles, forming a belt that spreads out transversely eight or nine 
miles. The Jura, Trias, and Permian, and heavy masses of Carboniferous 
rock, dip eastward along the Wahsatch, and, passing under a synclinal, rise 
again upon the end of Uinta Range. From the relative position of the 
rocks on both sides of the synclinal, it is evident that there has been a fault, 
and that the end of the Uinta has been elevated above the corresponding 
horizons of Wahsatch Range. The fault which is thus defined through the 
older rocks projects southward through the Cretaceous and the overlying 
Eocene beds, the trachytic eruptions reaching their greatest elevation at the 
south at Heber Peak, where the altitude is 10,138 feet. North of the 
synclinal between the Wahsatch and the Uinta the trachytes had a wider 
spread, extending eight or ten miles northeast from the little town of Peoria. 
In a northwest direction they recur upon the north side of Parley’s Park, 
and the northwest trend is continued in outbursts of trachyte which are 
seen in the valley of East Canon Creek, at its bend ten miles north of 


TRACHYTES. 587 


Parley’s Park, and again at Richville. The entire length of this trachytic 
vent is therefore about fifty miles. 

In Kamas Prairie and Provo Valley the Quaternary débris doubtless 
covers considerable portions of trachytic rock. Both in the region of Heber 
Peak and again north of Peoria, where an arm of the trachyte comes in con- 
tact with the Eocene rocks, it is distinctly later than the stratified sandstone. 
So, too, both the bodies which are seen in the valley of Hast Canon Creek 
are plainly later than the surrounding Tertiaries. It is the Vermilion 
Creek or the lowest member of the Eocene with which they are found in 
contact. There must, however, have been a great amount of erosion along 
the drainage of East Canon Creek before the ejection of trachyte, as it took 
place in the bottom of a well eroded canon. 

In middle Nevada, in the region of Dixie Valley, we have the next 
later member, the Green River group of the Eocene, overlaid by trachytes. 
The Bridger group has never been seen by us in contact with volcanic 
rocks, and the only time-fact about this great Provo trachyte field is, that 
it occurred either late in the Eocene or during the Miocene. The latter is 
known to be the age of the western Nevada trachytes, and there are no 
valid geological grounds for especially doubting that these are contem- 
poraneous. 

At the southern end of the outburst they appear to have overflowed 
the conglomerates of the Uinta group of Eocene, which here represents the 
same horizon as the Vermilion Creek beds to the north. The conglom- 
erates, both north and south of the Uinta, in the immediate neighborhood 
of the trachyte, never contain any trachyte bowlders, which must neces- 
sarily have been the case if the ejection had been prior to the deposition 
of the Eocene sediments. 

In several of the higher ravines in the neighborhood of Heber Moun- 
tains there are considerable accumulations of varied gravels and bowlders, 
among which are many fragments of trachyte. These probably belong to 
the Wyoming (Pliocene) conglomerate, which covers the neighboring ridges. 
Besides the superficial exposures, which are frequent over the whole tra- 
chytic field, good sections are obtained in Heber Canon, in the valley of the 
Provo, on the heights on both sides of Weber River near Peoria, and 


588 SYSTEMATIC GEOLOGY. 


throughout the valley of Silver Creek. In general, the whole eruption was 
quite free from breccia, and it is remarkable for so extended a field in that it 
is extremely rich in well crystallized minerals from one end of the exposure 
to the other. The exceptions to this are on the foot-hills northeast of the 
town of Medway, where there is a considerable deposit of stratified volcanic 
ash, indicating that during the early period of the eruption sands and 
rapilli accumulated in a small lake. The second exhibition may be seen in 
the valley near Silver Creek, above the head of Provo Canon, where there 
is a light-gray, trachytic tuff, with a slighly decomposed groundmass and 
large sanidin crystals, with needles and flakes of mica. 

On the canon walls between Kamas and Provo are highly porphyritic 
forms, having reddish, purplish, and greenish groundmasses, containing 
brilliantly white sanidins, earthy-brown hornblende, and much specular 
iron, and, in a few instances, considerable bronze mica. 

On the heights between Provo and the head waters of Silver Creek are 
some interesting purple and: apple-green trachytes, having a groundmass 
especially compact and semi-vitreous, in which are abundant glassy sani- 
dins; dark-brown, dark-purple, and black, more or less altered hornblende, 
with occasional flakes of biotite, and small, brilliant plagioclases, the micro- 
scope showing a dark-gray, globulitie base. 

Farther down Silver Creek, near Kimball’s, a similar trachyte was 
observed, very rich in sanidins, and having a good deal of plagioclase, 
hornblende, augite, tridymite, and apatite. And not far from Kimball's 
Station, directly north of the road, are trachytes of a rusty brick-red color, 
that have broken through the Cretaceous and Jurassic strata, which are 
more or less altered by contact with the trachyte. The only peculiarity of 
the rock is, that the hornblende is a little fresher than usual, and that besides 
the tridymite there is a large proportion of augite. 

Comparison of a great number of specimens from the whole field of this 
extensive eruption shows a single prevalent type; a rather fine-grained 
groundmass plentifully imbued with a glassy base, which for the most part 
is devitrified, carrying predominating sanidin, few but brilliant plagioclases, 
hornblende (often decomposed), and sparing augite; exceptional specimens 


showing a high proportion of bronze mica. It is a normal sanidin-trachyte, 


TRACHYTES. 589 


in which hornblende exceeds biotite. North from Parley’s Park, about half- 
way down to Morgan Valley, a body of trachyte occupies the hill slope on 
the right bank of East Canon Creek for two or three miles. A rather 
abrupt slope is exposed, made up of distinct horizontal beds, the habit of 
the rock being decidedly like an andesite. 

About four miles south of Weber Station, where East Canon opens 
out into a broad valley, is the northernmost of this chain of trachytic bodies. 
It occupies a narrow area along the right bank of the stream, and is for the 
most part surrounded and covered by horizontal Pliocene strata. It con- 
sists of a very coarse groundmass of sanidin and biotite, with little or no 
glass base. In the groundmass are highly developed sanidins of brilliant, 
glassy purity, and shining black biotites. Although it precedes the Pliocene 
beds which clearly overlie it unconformably, yet a considerable part of this 
eruption appears in the form of a rough, gritty, trachytic tuff, which must 
have been ejected when Morgan Valley was eroded to nearly its present 
dimensions and contained more or less of a lake. 

The great orographical feature of the Wahsatch is the line of fault and 
displacement which for a hundred miles has occurred through the heart 
of the range, severing it into halves, the western of which has been de- 
pressed to an unknown depth—certainly in the region of Cottonwood 
Canion 40,000 feet—below the level of the eastern. Nothing is more natu- 
ral than that this line should subsequently become the theatre of volcanic 
action. The smallness of the amount of actual ejecta is rather the most 
remarkable feature of the locality. This great north-and-south fault was 
crossed by a less powerful but remarkable line of east-and-west strain 
along the axis of the Uinta Mountains, the intersection of the two taking 
place in the granite region of the Little Cottonwood. It is here, in what 
are called the Traverse Mountains, that the most considerable trachytic 
eruptions have taken place. 

South of the granitic body of Lone Peak, a spur of hills projects west- 
ward to the middle of Jordan Valley, and beyond the river rises against 
the foot-hills of the Oquirrh. In the immediate valley of the Jordan the 
volcanic rocks are covered by accumulations of Quaternary and the ter- 
races of the Bonneville Lake period. The Traverse Mountains have 


590 SYSTEMATIC GEOLOGY. 


a trend a few degrees south of west, or approximately at right angles to 
the northwest trend of the great trachytic series that lies along the eastern 
base of the Wahsatch. The fissure that permitted the escape of these 
rocks started out from the great Wahsatch fault where the Cambrian series 
comes in contact with the underlying Archean granite, and continues 
through the unknown rocks deeply buried beneath the valley of the 
Jordan, finally cutting through the quartzites and limestones of the Oquirrh. 
The hills east of the Jordan rise about 1,200 feet above the level of the 
plain, and probably a considerable portion of their bulk is the continuation 
of the Archzean and granitic spur; but it is all covered now by the broad 
field of trachyte which occupies the whole surface. West of the Jordan 
the trachytic exposure is on a larger scale, the hills rise 2,000 feet above 
the valley, and the trachytes are seen abutting directly upon the Weber 
quartzites of the main ridge. 

Along the eastern foot-hills of the Oquirrh, the trachytes extend north- 
ward as far as Bingham Canon. Near the Wahsatch, on the eastern end of 
the group of hills, the trachytes are dark-bluish, reddish, and brownish 
rocks, composed of but a small amount of groundmass, in which sanidin 
and biotite are the principal secretions. There is so little groundmass that 
certain specimens have a granitoid look, suggesting some of the nevadites. 
While sanidin and biotite are the prominent constituents, there appear 
small plagioclases, unaltered hornblendes, and considerable olive-colored 
augite, and the microscope reveals apatite and magnetite. In immediate 
contact with the Lone Peak granite, the rock is an earthy, greenish-white 
mass, with the feldspars kaolinized and the groundmass decomposed beyond 
recognition. 

The western body of mountains beyond the Jordan consists also of 
sanidin-trachytes, rich in glassy feldspar and bronze mica, and possessing 
a very little hornblende. Here at the northern limit of the main body, at 
Rose Cation, hornblende and mica are more abundant and sanidin less, 
Throughout the middle of the group are dark, heavy, hornblendic tra- 
chytes, in which the proportion of plagioclase rises very nearly to equality 
with the sanidin, and the rocks approach the andesitic habit. 

Near Salt Lake City, about two miles up the canon of City Creek, 


OHV] 


TRACHYTES. 591 


the hills on either side of the stream are for a short distance (not over 
a mile and a half) formed of dark, reddish-brown trachyte. All around 
the sides of the body the Eocene Tertiaries are extremely soft, and 
the earthy accumulations effectually hide the relative ages of the two. 
There is little doubt, however, that the trachyte, like that east of the moun- 
tain, is more recent than the Eocene beds. This outburst is directly on 
the line of the great fault, which to the south has cut off the ends of the 
Paleozoic and Mesozoic strata, and to the north has split down the body 
of Archean rocks which forms the nucleus of the range. The rock shades 
from reddish-gray into light pinkish-gray, deepening in some cases into a 
dark chocolate. It has a rough, coarsely crystalline groundmass of feld- 
spar, hornblende, and biotite. Among the macroscopical crystalline secre- 
tions are abundant sanidin and a high proportion of plagioclase, deep-brown 
hornblende with the characteristic black border, yellowish-brown mica, 
and pale-green- augites. The microscope also shows an abundance of 
tridymite and quartz. An interesting microscopical peculiarity mentioned 
by Zirkel is the occurrence of minute fluid inclusions, with moving bubble, 
together with gas cavities in the pale, clear interior of certain hornblende 
sections. The augites contain none of the magnetite grains so common in 
basalts. Here again is one of those rocks which contain the minerals both 
of basalt and of rhyolite. 

Partly on account of the great geological interest of the region and 
partly as a study of canon erosion, I made in the year 1869 a short expedi- 
tion from Camp Halleck, Nevada, northeastward, by way of Thousand 
Spring Valley, to the basin of Snake River. In the lower and western 
portion of the same great interior basin there is an abundant exposure of 
lacustrine Pliocene rocks rich in a fauna comprising mammals, fishes, and 
mollusks, and also charged with the remains of arborescent vegetation now 
silicified. One of the most interesting features of that region was the inter- 
calation of sheets of basalt in the midst of the Pliocene series. This obser- 
vation, hastily made in travelling by myself, was afterward confirmed by 
Prot. O. C. Marsh. Pliocene rocks in disturbed positions form the divide 
between the basin of Utah and that of the watershed of the Columbia. 
The western exposure of these rocks on the divide in the region of Toana 


592 SYSTEMATIC GEOLOGY. 


and westward as far as Bone Valley, consisted, as was shown, of rhyolitic 
glassy tuffs. We have seen, when examining the Truckee Miocene strata 
of the Kawsoh Mountains in western Nevada, that in the process of up- 
heaval the Miocene trachytic tuffs were invaded by rhyolites which accom- 
panied the post-Miocene disturbances. The rhyolitic tuffs of northwestern 
Utah and northeastern Nevada, already proved to be Pliocene by carrying 
fossil vertebrate animals referred by Leidy to the age of the Niobrara Plio- 
cene, are still further confirmed as such by the nature of their material, 
which belongs to the age of the rhyolites, which from the data in the Kaw- 
soh Mountains we are able to place at the beginning of the Pliocene. We 
have, therefore, in the region of the divide between the Great Basin and 
that of the Shoshone, early Pliocene beds of volcanic origin, carrying the 
Niobrara fauna, and in Boise Basin two divisions of lacustrine Pliocene, 
both horizontal, one previous and one subsequent to certain of the basaltic 
eruptions. It is all but certain that the sub-basaltic Pliocenes are the 
equivalent in age of the rhyolitic Pliocene division of western Nevada. 
The post-basaltic Pliocenes of Boise Basin are to be directly correlated 
with those of the Humboldt valley and much of the Great Basin country. 

The eastern portion of the Shoshone Basin has for its surface a broad, 
nearly level field of black basaltic beds which are seen by the magnificent 
exposures of Snake Canon to overlie an undulating, hilly surface of prior 
trachytic eruption. In this portion of the basin no lacustrine sediments are 
seen, and it is evident that none were laid down here, since the underlying 
trachytes belong to an age prior to the earliest Pliocene deposit. Through- 
out the great basaltic plain is traced the sinuous line of the Shoshone 
canon, a gorge cut sharply down through the volcanic beds from 400 to 
700 feet. 

Geologically and scenically the neighborhood of Shoshone Falls is the 
most interesting point of the cafon. Plate XVII. is a view taken from a 
point a little below the surface of the plain on the left bank of the river, 
looking east. 'The horizontal sky-line is seen defined by the basaltic tables 
and the middle of the field is occupied by a general view of Shoshone 
Falls. Plate XVI. is a nearer detailed view of the Fall itself plunging over 
a trachyte cliff 190 feet high. The volume of the river in its fullest stage 


‘an 


TRACHYTES. 593 


is far less than that of the Niagara, but the breaking up of the brink of 
the Falls by deep reéntrant angles, renders the cataract one of the most 
picturesque in the world Plate XVIII. is a view down the gorge looking 
over the top of the fall, and is of especial interest as showing the narrow, 
abrupt character of the cation. Plate XIX. is a detailed bit on the left 
bank of the canon, showing the light-colored, easily eroded trachyte mass, 
with a vertical exposure of about 200 feet, capped by the level sheets of 
basalt which extend down the river uninterruptedly for many miles. 

From a few miles above the Shoshone Falls the river was followed 
for ten miles of its downward course, and although the exhibition of under- 
lying trachytes was almost continuous for that distance, no variation in 
the type was observed. The chief interest of this region, besides the evi- 
dent relations of the two types of the volcanic rocks, is the great horizontal 
extent of the basaltic beds. Whether they flowed from the two flanks of 
the valley, or from far eastward in the region of the Teton group, is un- 
certain, but the exposure is nevertheless of interest from the great distances 
that single thin sheets of basalt are seen to have flowed. The well known 
power of retaining a high temperature and of long continued fluidity on 
the part of the basalts, is here displayed to remarkable advantage. From 
a brief inspection it is my belief that single sheets have flowed at very 
gentle angles for fifty or sixty miles. The region is further interesting as 
a proof of the intensity and extent of post-basaltic erosion. One is not 
surprised, in studying the flanks of steep mountain ranges, to find them 
scored by profound Quaternary cations; but to see a long, level lava 
plain gashed by a cafion from 300 to 700 feet in depth shows an energy 
on the part of the slowly flowing rivers which is positively marvellous. 

On the eastern flank of the Aqui Mountains, at the base of Bonneville 
Peak, near the parallel of 40° 30’, is a small region of trachyte, exposed 
at the forks of South Willow Creek. The geological characteristics are 
well shown on the western half of Map III., where it is seen that the range 
is composed of a body of Lower Coal Measure limestones thrown into a 
curve which on the eastern edge of the mountains abruptly bends over into 
a steep, easterly dip. The western half of the range is a great body of 

‘ambrian quartzites faulted wp into a position even higher than the geolog- 
38 K 


594 SYSTEMATIC GEOLOGY. 


ically superior limestones. Through the sharp flexure of the limestones a 
fissure has occurred, from which a body of trachytes has outpoured, cover- 
ing the eastern slope quite to the plain of the Quaternary desert. There 
are no recent rocks anywhere in the neighborhood to afford a clew. to the 
date of the eruption. North and south of the entrance of Willow Caton 
the hills are covered with accumulations of red and gray trachytic ash. The 
groundmass is fine and porous, varies from reddish-gray to white, and con- 
sists of an intimate mixture of crystals of feldspar, both orthoclase and pla- 
gioclase, together with a great deal of globulitic glass. Macroscopically the 
crystalline secretions show an enormous preponderance of distinctly hex- 
agonal biotite laminze and a few hornblendes, the microscope revealing a little 
apatite. 

An exposure of trachytic rock is seen at White Rock Springs, near the 
southern end of Cedar Mountains. The ridge already described as a double 
fold of Lower Coal Measure limestones is marked by the occurrence of a 
body of andesite at the important angle of flexure of the range. Directly 
east of the andesites occurs a small body of trachytes occupying an east- 
and-west region entirely enclosed by limestones, except the very eastern 
extremity, which passes under the Quaternary of the plain. The greater 
part of this exposure is of rough, reddish, trachytic breccia, above which 
rise the white rocks from which the locality takes its name. They are 
domed masses, about 300 feet high, of grayish-white quartziferous trachyte. 
These bosses of rock have such smooth, even sides that they are exceedingly 
difficult of access. The rock is a crystalline aggregation of sanidin (the 
individuals of which sometimes reach an inch in length), brilliant black 
prisms of hornblende, flakes of biotite, and cracked, rounded granules of 
quartz. It shows a close resemblance to the family of quartziferous 
trachytes of Elk-Mountain. 

It would seem that all the trachytes of the Salt Lake region naturally 
group themselves into two main systems of eruption—the great body east 
of the Wahsatch, with its northern continuation, which marks one of the 
orographical faults of the Wahsatch; and that of the Traverse and Aqui 
mountains and Cedar Range, which, though irregular in trend, is practi- 
cally at right angles to the first-named series. 


TRACHYTES. 595 


Over the whole broad desert lying to the north and west there are no 
trachytes, with the exception of a small body on Peoquop Creek, in the 
northern part of the eastern half of Map IV. Peoquop Creek drains 
through Thousand Spring Valley a few miles north of the Pacifie Railroad, 
and traverses a low region of which the geology is quite simple. It consists 
of island-like spurs and hills of Weber quartzite, surrounded and overlaid 
by horizontal strata of Phocene. Through the quartzites has outpoured a 
small body of trachyte,-over and around which the Pliocene strata have 
been deposited nonconformably. It forms a long north-and-south ridge, 
with several dome-like points. The rock is more or less decomposed, and 
is characterized by pores and cavities filled with both calcite and chal- 
cedony. It is made up of sanidin, plagioclase, and hornblende. The two 
feldspars are present in about equal proportion, and the rock is to be classed 
with the earlier plagioclase-hornblende-trachyte which is characteristic of 
the region of Washoe. 

Humboldt Range, although the most extensive and lofty in Nevada, is 
conspicuous for its paucity of volcanic rocks. Minor rhyolitic eruptions 
have taken place in the northern part of the range, but the only trachytic 
occurrence is a small body a few miles north of Cave Springs on the east- 
ern base of the range. Here a limited flow of grayish, highly crystalline 
trachyte has burst out through a fissure in the Lower Coal Measure lime- 
stones, its appearance being accompanied by an unusual amount of shatter- 
ing of the limestone rocks. ‘The exposure isa low, rugged spur, surrounded 
on all sides by limestone. It is essentially a sanidin-biotite-trachyte, 
although triclinic feldspars and hornblende are present in small quantities. 
The plagioclases are noticeable macroscopically for their great size and bril- 
liant surfaces. The microscope reveals prisms and microlites of apatite, 
besides quite fine particles of hornblende entering into the groundmass after 
the manner of powdered hornblende in propylite. Rare macroscopic 
quartzes are present, but the microscope detects none in the groundmass. 

In the upper valley of Susan Creek are two small bodies of trachyte, 
separated from each other by horizontal strata of Pliocene and the Quater- 
nary valley deposit, both of which are later than the trachytic eruption; and 
it is most probable that the two trachyte bodies have a connection beneath 


596 SYSTEMATIC GEOLOGY. 


the Pliocene. More recent rhyolites overlap both the trachyte bodies. 
Of these two exposures, that on Coal Creek, at the base of Seetoya Range, 
has a colorless feldspathic groundmass in which are enclosed sanidins, plagi- 
oclases, and a few biotites, the microscope revealing a little titanite. The 
more southern of the two outcrops is a pale-reddish, earthy trachyte re- 
sembling domite. Its base is decidedly glassy and considerably globulitic, 
and carries much fine crystalline feldspar. The most remarkable points 
about this rock are, that it contains, even macroscopically, rose-colored gar- 
nets in granular aggregations, and that there are also disseminated through 
the groundmass bright prussian-blue, hexagonal grains, referred by Zirkel 
to haiiyne. Zirkel remarks (Volume VI., page 151) that the occurrence of 
such garnets in trachyte is only recorded besides of specimens from the 
island of Ischia. 

One of the most extensive as well as interesting trachyte localities in 
Nevada is that in the northern part of Pinon Range. The lofty body of 
mountains here at its northernmost extremity consists of an anticlinal with 
a trend a little east of north. This broad fold involves strata of the Cam- 
brian, Silurian, Devonian, and Carboniferous ages. The continuity of the 
great axis is suddenly broken by an east-and-west fault, which has been the 
theatre of deep dislocation. The group of hills to the north, formed of 
the united River and Elko ranges, in which the most ancient neighboring 
rocks are the Uinta quartzites, has retained its natural level, while the Pinon 
anticlinal has been lifted from a great depth, exposing the lower strata. 
Besides the east-and-west break described, another powerful fissure passes 
in a meridional direction along the eastern base of the range. From out of 
both these cracks an enormous trachytic flood has been ejected, surrounding 
and burying the edges and ends of the uplifted Pinon strata. In Dixie 
Pass the sharply eroded edges of the Paleeozoic strata plunge suddenly 
down beneath a series of rolling trachytic hills, which sweep around 
southward, coming in contact successively with the Devonian and the Silu- 
rian of the western half of the Pinon anticlinal, then with the Cambrian 
nucleus of the fold, and afterward to the south bounding the Silurian 
and Devonian of the easterly dipping member of the group. There is no- 
where a more interesting instance of the direct and obvious connection of 


’ 
. 4 . i 
. 
SS r 
‘ i, ‘ 7 
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& 
BF ne ai 
aM yan sai,’ * : ; 
Hn 


TRACHYTES. 597 


volcanic eruption with mountain dislocation. The trachytes thus exposed 
extend about twelve miles north-and-south and four to six miles east-and- 
west, the surface being high, rolling ridges and spurs, those bordering on 
Dixie Valley forming a chain of characteristic dome shapes. Along their 
eastern margin for a considerable distance these trachytes overlie the up- 
turned caleareous shales of the Green River Eocene, and to the south are 
themselves overlaid by a subsequent flood of rhyolite and the horizontal 
Pliocenes of Huntington Valley. The higher spurs and domes all show a 
rounded form and an absence of any conspicuous bedding. The general char- 
acter of the predominating eruption was that of broad, massive accumula- 
tions, and even the most isolated and conoidal of the trachyte domes show 
no evidence of the structure of a true voleano. The main material, and that 
of all the later eruption, is of brownish and reddish sanidin-trachyte, with 
a very coarse, rough, friable groundmass, composed of vitreous sanidin and 
magnesian mica, in which a multitude of the larger crystals of both are in- 
cluded. There is a very close resemblance between certain specimens of 
this rock and the Sugar Loaf trachytes of Washoe. They exhibit the same 
method of mingling the biotite and sanidin, and the latter is in the same abun- 
dantly fissured condition as the former. At several places near the Cambrian 
and Silurian foot-hills, and along the northern slopes of Dixie Hills, deeper 
erosion has exposed a lower family of trachytes These are characterized 
by the sparing presence of biotite and the decided predominance of horn- 
blende, which occurs, both in brilliant black crystals and in earthy, gray 
prisms, associated with plagioclase which equals or exceeds the sanidins. 
Among these hornblendic trachytes the groundmass is far more compact, 
the rock is evidently bedded and has a habit approximating to that of ande- 
sites. The only very similar rock obtained in the Fortieth Parallel area is 
that which has been described in Volume IIL, Chapter IL, from the cross- 
spur at Virginia and Washoe, from which this only differs in having rather 
smaller plagioclase crystals. In fracturing the rock, it is noticeable that it 
breaks most easily parallel to the planes of bedding, and that all the larger 
crystals are arranged in such planes that the surface of a fractured speci- 
men usually displays several split hornblende prisms with brilliant black 


surfaces and large slabs of feldspar. It is interesting to note that this 


598 SYSTEMATIC GEOLOGY. 


plagioclase-hornblende-trachyte, which verges very near the andesites, is 
older than the sanidin-biotite-trachyte, the same sequence being observed 
at Washoe. 

At Palisade Cation the Humboldt has worn a gorge through an area 
of trachyte about five or six miles from north to south by four from east to 
west, along the course of the river. The hills to the north rise 1,500 to 
1,800 feet high, and to the south reach about 1,000 feet. In the very 
middle of this trachytic exposure, in a ravine which enters the canon from 
the north, erosion has laid bare an underlying massive andesite, which again 
occurs on Emigrant Road directly north of the northern limit of the 
trachyte body. It is plain that the fissure which gave vent to the trachyte 
was a reopening of the weak line of the andesitic break. So many oro- 
graphical periods had disturbed the whole Cordilleras prior to the Tertiary, 
that there were innumerable lines of weakness, which the earlier Tertiary 
eruptions easily found; and although the period of each successive volcanic 
family enlarged the limits over the previous one, yet in many instances 
the later voleanic rocks are found to follow the fractured lines of their 
immediate predecessors, as in this case. Although the whole body is 
essentially a group of sanidin-trachytes, the hills north and south of the 
canon present some different varieties. The cliffs along the southern wall 
are of normal sanidin-trachyte; the brownish-gray groundmass, composed 
of sanidin and biotite, containing larger crystals of these two minerals. 
The microscope reveals the presence of a few hornblendes and apatite. 
Upon the northern wall of the canon, in the hills which form the main 
eruption for several miles, are observed more recent trachytes than those 
just mentioned. They have a light-gray, porous groundmass composed 
of biotite and sanidin, in which are remarkably perfect yet earthy prisms 
of hornblende, together with interesting casts of these crystals where all 
but the granulated border-material of the hornblende has been removed. 
The sanidins always obviously outnumber the hornblendes. 

The body of quartz-propylite which extends along the ridge of the 
Cortez Mountains, south of Wagon Canon, is margined along the west by 
a narrow exposure of sanidin-trachyte, which to the west is covered by 
rhyolites. The groundmass resembles that of propylite, from the amount 


TRACHYTES. 599 


of small hornblende crystals that enter into its composition. Small sani- 
dins, lamin of partially decomposed biotite, and a few well preserved 
hornblende crystals make up the list of crystalline secretions. But for the 
predominance of sanidin over plagioclase, the rock, from the peculiar dispo- 
sition of the hornblende, would be closely related to the propylites. The 
microscope shows in the biotites an interesting interposition in the laminz 
of colorless muscovite. Zirkel also describes the feldspars as being covered 
with a glittering dust, the product of alteration, and probably calcite. The 
instrument also reveals apatite. Between the trachyte and the neighboring 
volcanic rocks, the question of age is too obscure to allow of any definite 
conclusions. 

The Wahweah Mountains, of which only the northern parts come 
within the limits of our map, lie, as do most of the Nevada ranges, between 
two open desert valleys. That upon the west is much the lower. Large 
parts of the Wahweah group are formed of tabular fields of trachytic rocks 
which all slope toward the lower or western valley. Above the general 
plateau-like surface rise rugged hills and points, and the slopes are scored by 
deep ravines and canons, which afford excellent exposures. The northern 
part of the mountains is composed of granite, overlaid by Silurian and 
Devonian strata, which, in extending southward, pass beneath the great 
trachytic covering. Hxamination of the specimens collected here discovers 
a rich variety, representing nearly all phases of the trachytic family. There 
are quartziferous trachytes which in the ordinary microcrystalline ground- 
mass carry brilliant sanidins, some fresh plagioclase, and well developed 
biotite, with large hexagonal crystals of quartz surrounded by a fibrous 
spherolitic crust. A second variety is a typical sanidin-trachyte with 
large sanidins, abundant biotite, plagioclases, and a little hornblende with 
which decomposition has usually proceeded very far. The microscope 
reveals apatite and haiiyne. The plagioclase-hornblende-trachytes, in 
which triclinic feldspars rise nearly to the proportions of sanidins and the 
hornblendes greatly exceed the biotites, also occur, and last of all comes 
true augite-trachyte with a dark, homogeneous groundmass, enclosing 
large numbers of plagioclases, macroscopic augites, and microscopic apatite. 


The relative ages of these varieties were not worked out. 


600 SYSTEMATIC GEOLOGY. 


On Jacob’s Promontory, a little group of hills in Reese River Valley, 
north of Jacobsville, intimately associated with some rhyolites which have 
partially overlaid it, is a small body of gray trachyte, which besides the 
prevailing sanidin contains some plagioclase and augite, with, however, 
a predominance of hornblende. The habit of this rock resembles the 
andesitoid gray trachytes of Virginia. 

Not the least remarkable among the isolated outbursts of trachyte is 
that which occurs on the heights of Havallah Range, near Cumberland, 
having poured out near the junction of the Triassic quartzites with the Star 
Peak group. The general inclination of the structural lines of the trachyte 
is to the east, and its summit is that of a high ridge rising in several rude 
conical points. The rock itself is a very porous sanidin-trachyte, of a dull 
gray groundmass, carrying sanidins from an inch to an inch and a half in 
length, many of the crystals being dislocated and broken. Small flakes of 
brownish biotite are scattered through the groundmass; and that which 
above all distinguishes this trachyte is the occurrence of large limpid gran- 
wes of quartz, a mineral which does not enter into the composition of the 
groundmass. It is most nearly allied to those trachytes of the Elk Head 
Mountains, in Colorado, which also carry an abundance of macroscopical 
quartz, but none entering into the rather basic groundmass ; the quartzes in 
these instances playing a peculiar réle, since they are enclosed in a ground- 
mass by no means either as acidic or as glassy as in the rhyolites. 

In Pine Nut Canon, of Pah-Ute Range, east of Chataya Peak, is a body 
of trachyte which has broken out east of the diorite, immediately followed 
eastward by subsequent eruptions of rhyolite. The habit of the rock is 
distinctly trachytic. The colors are gray, yellow, and brown. For the 
most part, the groundmass is a combination of feldspar, opacite, and ferrite, 
and for a limited portion of the body is decidedly rhyolitie in type, con- 
sisting of axially fibrous bands separated by masses of felsitic substances 
rich in ferrite and opacite. The rock contains no quartz; but the sanidins, 
reaching a quarter of an inch in diameter, are peculiarly brilliant in lustre 
and at times are drawn out, showing an almost silky fibre like the threads 
of pumice. The outcrop is limited, occupying a low position on the flank 


of the range, and has no orographical importance. 


TRACHYTES. 601 


The chain of mountain elevations consisting of the Pah-tson and 
Kamma groups, really part of the Montezuma system, is continued north- 
ward by a range of hills having its rise a little north of Indian Spring and 
extending beyond the northern limit of Map V. The main body of the 
southern end of the range is formed of trachytes, which tower above the 
desert valley of Quinn’s River about 3,500 feet. The culminating summit 
and the ridge extending northward, as well as the abrupt, promontory-like 
southern front of the range, are made up of sanidin-trachytes, which, in 
turn, are broken through and overflowed on their western base by rhyo- 
lites. At the eastern base of the hills, directly east of the culminating 
summit, the trachytes are seen to overlie the slates of the Jura, while upon 
the west they are indistinctly connected with the upturned Miocene beds. 
The trachyte itself is of a variety of purplish-red colors, having a decidedly 
conchoidal fracture. It is mostly very fine-grained, consisting of a ground- 
mass of sanidin, opacite, and magnetite, in which are embedded no macro- 
scopic crystals except a few small, brilliant sanidins. 

A small and rather unimportant trachytic outcrop occurs in the low 
foot-hills at the northeast point of the Kawsoh Mountains, directly oppo- 
site Carson Lake. Here, rising above the Quaternary desert slopes, are 
low hills a few hundred feet in height, which above are conspicuously 
capped with black basalt. The material of the hills is a fine-grained sani- 
din-trachyte, of a dark, grayish-brown color, with often a dull earthy exte- 
rior. Indistinct beds make up the mass of the hills. Lithologically there 
are no points of interest about the trachyte, except that it is rather com- 
pact, and when undecomposed breaks with an unusually lustrous fracture, 
and contains in the gas-cavities and cavernous spaces considerable amounts 
of tridymite. Professor Zirkel, who calls attention to this fact, also notices 
blood-red laminz of specular iron. 

Of the trachytes of Lake Range, which evidently occupy a consider- 
able portion of its body, only those bordering Pyramid Lake and the ex- 
tension of the same system at Anahé Island have been examined. The 
western slopes of Lake Range, and the mass of trachyte of the island itself, 
are rugged piles, showing little or no tendency to lines of flow or bedding. 


The mountain surfaces are more or less eroded by ravines, which display 


602 SYSTEMATIC GEOLOGY. 


the rough, dark slopes of trachyte. Under the hammer the rocks of this 
region break with a rough, hackly fracture. In the hand specimens they 
are almost always of dark grayish-brown or reddish-brown colors, the 
groundmass consisting of fine sanidin with magnetite, ferrite, and opacite, 
in which are frequent large, vitreous sanidins and occasional but rare bio- 
tites and hornblendes. 

Of the trachytic hills which form the northern part of Virginia Range 
where it descends to the level of Mud Lake Desert, Mr. Hague says :* 

“North of the basaltic body, Virginia Range terminates in a group of 
low hills, which border Pyramid Lake on the northwest and connect with 
the southern end of the Madelin Mesa. Astor Pass cuts through these 
hills, connecting Pyramid Lake with Honey Lake Valley of California, 
and lies below the level of the ancient Lahontan Lake, the calcareous 
tufas covering the flanks of the hills, and showing conclusively the flow of 
those alkaline waters westward beyond the boundary of Nevada. 

“On the geological map, these hills are colored as trachytes; it is 
probable, however, that rhyolites are represented here; indeed, the entire 
group belongs to that class of rocks which stands on the border line between 
these two types of acidic rocks. They are characterized by reddish-brown 
and gray colors, and a decidedly crystalline texture, with the individual min- 
erals usually well developed. One of the most striking rocks of the region, 
and one characteristic of Astor Pass, is found near the entrance of the pass, 
about four miles northwest from Pyramid Lake, where it forms broad 
table-like masses. The prevailing color of its groundmass is brownish 
gray, in which, forming the greater part of the rock, are porphyritically 
enclosed crystals of feldspar, mica, hornblende, and quartz. Many of the 
feldspars have a dull white color, quite unusual in rhyolites, and are fre- 
quently three quarters of an inch in length, carrying impurities which may 
be recognized by the aid of an ordinary magnifying glass. Mica is very 
abundant and of a brilliant black color, while the hornblende, which is also 
black, plays quite a subordinate part. The quartz-grains are large, but are 
by no means frequent, and resemble those usually found in that some- 
what limited group of quartz-trachytes; that is to say, they appear more 


* United States Geolog cal Exploration of the Fortieth Parallel, Volume Il., Chapter V. 


TRACHYTES. 603 


like an accessory mineral than a primary constituent of the rock. They 
are quite clear and colorless, and apparently free from microscopical im- 
purities. Under the microscope, mmute crystals of apatite may be recog 
nized. The presence of quartz and the microscopical structure of the 
groundmass relate this rock to the rhyolites.” 

The most important body of trachyte upon Map V. is that which is 
displayed in the canon of the Truckee, and which forms the body of Vir- 
ginia Range thence northward to Pyramid Lake. The summit and slopes 
of this elevated mountain body are for the most part made up of broad, 
thick beds of dark earthy-brown and reddish-brown trachytes. From 
Ormsby Peak, an elevation of 9,388 feet, down nearly to the shores of 
Pyramid Lake, are deeply scored canons which show lofty, rugged slopes 
made up of the edges of heavy trachytic beds. With nothing like the 
evidences of flow that one sees in many rhyolitic regions, there is never- 
theless a tendency to form sheets, and a tendency of the sheets to slope 
both to the east and west and down the flanks of the range, the general 
impression being that of a body having its source of outflow near the heart 
of the range, with each paroxysm of ejection superposing a new bed which 
declined slightly toward the plains on either side. A cross-section of these 
trachytic tables would show a low, broad arch, resembling the curve of a 
flat anticlinal. This structure, very common in the basaltic ridges of the 
region, is certainly indicative of a considerable amount of fluidity retained 
for some time after the actual delivery of the trachytic matter from the vol- 
canic vent. More commonly the trachytic eruptions are distinctly structure- 
less—that is to say, they betray no lines of flow and no bedding by which 
the material may be traced to the region of vent. This arched ridge, how- 
ever, plainly shows the existence of a central fissure following approxi- 
mately the axis of the range out of which the still plastic trachyte poured, 
and from which it flowed down to the east and west. This field of trachyte 
surrounds and overflows the melaphyres, propylites, andesites, and dacites 
of the Berkshire Canon region, makes an island of a summit of diorite 
south of Sheep Corral Canon, and forms all the low hills bordering the bot- 
tom of Truckee Canon from Clark’s Station westward nearly to Wads- 


worth, except in the lower part of the canon, where a deeper erosion has 


604 SYSTEMATIC GEOLOGY. 


laid bare the earlier propylites and diorites. Upon the eastern flank of 
the range, and in the region of. Spanish Peak, rhyolites have broken out 
upon both sides of the trachyte, and toward the south it is completely 
overlaid and bounded by deep and extensive accumulations of gray basalt. 
A considerable variety of trachytes is found in this great field, of which the 
following are some of the more important and interesting. 

The trachyte which appears upon the south side of the lower portion 
of Truckee Canon, occupying an intermediate position both as to age and 
superposition, is a light-colored, friable rock, containing a considerable 
amount of glassy base, varyingly devitrified, in which are embedded sani- 
din, hornblende, and biotite. The glassy material and the sanidins are 
sometimes slightly fibrous, suggesting a tendency toward pumice. Besides 
these minerals, the microscope discovered to Professor Zirkel augite, apa- 
tite, and biotite. The rock, therefore, owes its interest to the concurrence 
of augite and sanidin. On either side of the river north of Truckee Ferry 
is also a sanidin-trachyte, rich in magnetite, but containing neither augite 
nor magnetite.* Directly overlying and immediately subsequent in age to 
these dark purple sanidin-trachytes are beds of dark, loose, reddish and 
brown trachytic breccias, containing blocks up to the size of a foot or two 
in diameter, the whole held together by a friable mass of trachytic rapilli 
and fragments. It is noticeable that a small proportion of augite is found 
in all the hand specimens we collected. Directly over this are lofty blufts 
with several hundred feet of precipitous front, composed of a pure gray augite- 
trachyte varying from light ashy-gray to dark, almost basaltic shades. It is 
distinctly bedded in horizontal tables, and would at once pass for a rather 
acidic basalt. More than any other trachytes of massive eruption in the 
Fortieth Parallel area, this occurrence displays the distinct habit of a sheeted 
flow, a habit ordinarily confined to the true basalts, the augite-andesites, 
and rare instances of hornblende-andesite which came to the surface in an 
exceedingly fluid condition. The joinings and superficial cracks of these 
gray trachytes are perpendicular to the horizontal flows, producing the 
ordinary bluff edges characteristic of basalts. The rock itself is of an ex- 


tremely fine-grained eroundmass, in which only a few feldspars can be dis- 
to} oO ’ v } 


* For analysis, see Volume II., page 833. 


SE 


“sisAyeue 


jo Jaquinyy 


144 
145 
146 


147 


148 


149 


TABLE OF CHEMICAL ANALYSES. X.—A.-UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. 


Trachytes. 
% 
ee e a ; Oxygen ratio of—| 5 “4 
sp Locality. Analyst. Si At Fe Fe | Mn | Ca Mg | Na K Li Ss Total SS | | 20,0 
Es =| ‘ gravity. R/|RIg De 
Zz = mio st 
143 | Truckee Ferry, Nevada - - - - | R. W. Woodward 50-36 17-00] 6.12] 3.84] 0.30] 8.85] 3.02] 3.21] 1-95] - -|CO?+HO] 5.35] 100.00] 2.6,2.7 | 58:]| 9.75] 26.86] 0.579 
26.86 7.92 z.83 | 0.85 | 0.06] 2.53 miaxiilimmo.83 | 0.33)| . ee mies a 8 aa peel fede o || as. x 
Gs wy = 5 5 9 a 50:03] 16.99| 6.05] 3-86] 0.42] 8.81] 2-98] 3.33] 2-27| - -|CO?+HO] 5.26] 100.00 ga 5.89 | 9.73] 26.68] 0.585 
26.68 7-92 1.81 0.86 0.09 2.5r 1.39 0.86 0,38 ot oe oe Sores ie else lee ted | ae 
144 | Ridge of Divide between Slater’s and @ 53-12) 14.54] tr. 6.01 tr. 6.01 e|| Keely) oo secant -58| 100.02 |2.7, 2.7, 2.7] 668] 6.77] 28.33) 0, 
Southwest Fork of Snake River. 28.33 G7 || ao BEB || o 9 1.72 Bs 0.78 ° 2 FP aaa ce G0 Us b yi alpsoun 4 oe 
q GF @ 8 e 53:25| 14-42] tr. 6.00] tr. 6.01} 5-06] 3:13) 4-58] - . Do oso 7.63| 100.08 a 8 6.66 | 6.72] 28.40] 0.471 
28.40 6.72 tote 1.33 aly 1.72 2.02 0.81 0.78 races Sens b fis ae ee ‘eure || gated bears | eae 
145 | Leucite Hills, Wyoming - - - - Gs 54.42| 13.37| 0.61] 3:52) - + | 4.38 6-37] 1.60] 10.73] tr. | CO? 1.82 2.76 99-58 |2-2, 2.2, 2.2] 6.8} 6.4r| 29.02] o.455 
29.02 6.23 | 0.28 | 0.78 | . . r.25 | 2.55 | or 7:82 |e eee a ome ett polska Aull ow 
Gi 3 Sag or w Geile nic ai oe) 6 o|] > || /GyAlibwersts 3. a 6 4 50 
146 | Purple Hill, Truckee Canon, Nevada « 6.51| 19.61 -10| 0.98| 0.11 6 tr. Sates 0.40] 100.0 2.0, 2.6 4.97 | 10.67] 30.14] 0.518 
Dees) 9 5 9 3307] 4 5 5) 
30.34 | 9.74 z.53 | 0.22 | 0.02 0.62 SS iieG Salina 
« “« “ 56.45] 19-85] 4.95] 0.97] 0-11 3:84. tr. Ce Ro 0.38] 100.06 A ae 4:95 | 10.73] 30.10] 0.520 
30.10 | 9.25 1.48 | 0.21 0.02 0.65 oo <c ae ee 
147 | Mount Shasta, Red Butte - - -|W.G. Mixter -| 60.44) 18.12) . .| 5-16 mA || oo oo 6 0.89] 99-79 0 a 5.60) 8.44] 32.23] 0.435 
32.23 Gye |! oo T.14 0.21 oan aac 4:46 | 10.16] 32.23] 0.453 
a ae oo GB - | 60.71) 18.32] - - 5:05 rers|| oo Stee 0.79| 100.16 F i609 5.6r | 8.53] 32.38] 0.436 
32.38 8.53 aie I.12 0.21 06 Ta 10 4.49 | 10.21) 32.38) 0.457 
148 | Mount Rainier, Washington Territory) O. D, Allen - - | 61.62] 16.86] . .| 6.61 HG! Gp) Go 00 99:42) + + ER) PALI AE lay ocho 
32.86 alle 3 AG) 0.28 a 4.03 | 10.05] 32.86] 0.428 
“ « “ “ - -| 61.78| 16.69] . .| 6.62 1260)| eae O. -Ov-4 og 99:38 my 5:49 | 7-77| 32.95] 0.402 
32.95 AM | oo 1.47 0.28 Aen 4.02] 9.98| 32.95} 0.425 
149 | Divide between North and Middle | R. W. Woodward] 6r.95| 16.75] tr. | 5-53 3-48} tr. | . . . | 422] roo.r2| 2.6, 2.7 | 518) 7.80) 33.04) 0392 
parks. 33-04 7iBoti|| eee 1.23 0.59 Ae <n Ps 3 eel icone 
« “ “ “ 61.95| 15.80] tr. 5.76 Episel| tie, o -p %0 1-34| 99-73 cine 5.29 | 7.36] 33.04] 0.382 7 
331040 | ey.a60) |= tas eeaxe28 059 | 2. aes of NE ao pbs || ctvon| Crees | ease re 


TAH 


*sisk[eue 
jo qraquinyy 


| 


5° 


- 


151 


152 


153 | Be 


154 | V 


155 


156 


TABLE OF CHEMICAL 


ANALYSES. X.—B.—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. 
Trachytes—(Continued.) 


s ai | é lGayeen ratio of—| 5 Z 
22 Locality. Analyst. Si At Fe Fe | Mn | Ca | Mg K Li 3 Total. air ee 
35 es R| RI] Si |RSS 
a = los 
150 | Cross-spur Quarry, Washoe - - R. W. Woodward | 63.13] 16.00] 4.34] 1.52 4-45| 2-07 2.65 2.00] 100.03 3:88 | 8.75 | 33.67 | 0.375 
33-67 7-45 1.30 0.33 1.27 0.83 0.45 3 aa gs | oe 
I5r | Mount Hood - - - = - - us 63-28] 17-96] 1.81] 3.16] tr. 5-34] 2-50 2.06 0.12} 100.04 4:55 | 8.90 | 33:74| 0.398 
33-74 8.36 | 0.54 0.70 5.52 1.00 0.35 ee yc 
ee S09 SBS us 63.18| 18.06] 1.92] 3-15] tr. Basil edo 2.05 0.10] 100.20 4:59 | 8.98 | 33:69) 0.402 
33-69 | 8.41 057 | 0.70 | . 1.52 1.04 0.38 : 5 re 
152 | Mount Rose, Washoe- - - @ 63-30| 17-81] 3.42| 0.83 +12)|| 2.07 2.26| tr. 0.88 99-96 3.95 | 9:32 | 33:75) 0.393 
33-76 | 8.30 r.02 | 0.38 1.46 | 0.83 0.38 ee ae 0 ea are 
as ce apie a 63-13] 17-54 -22| 0.8 5-15| 2-06 2.22| tr. 0.95 99-54 3.98 | 9-13 | 33-67) 0.389 
3°13 | 17-5 3 
33-67 8.17 0.96 0.18 147 0.82 0.37 oa oO bo Grell & t 
31 n Us Sea ti jo}! 2-22 fo) tr. 2.18] 100.28 4,60 | 7.16 | 34.57] 0.340 
153 | Between Provo and Silver Canon, 64-82 | 15.37 1008 : ae 4-9¢ Be 3:03 : ae a. 3:47 | 8.86 | 34:57] 0.356 
Wahsatch Mountains. 34 57 7-16 : 1.13 4 
~~" 
tr. 2.1 100.2 4,60] 7.16 | 34.04.) 0.339 
e : = ‘ 64-93 oe! a 1.13 Be 2B . é . 3 347 | 8.86 | 34.64) 0,356 
z r 3:77 | 7:37 | 36-16 | 0.308 
154 | Volcanic Ridge, Peoquop Range Gj 67-81 | 15-83) tr. 3:41 tr. I 73 100.06 SH 
36.16 7-37 0.76 . a 
.82 | 7.33 | 36.05| 0. 
“ “ “ «“ 67-60} 15-74 tr. 3.47 tr. 1-75 99:96 3.82] 7.33 | 3! ie 9.309 
36.05 7-33 e 9 0.77 a8 eet i $ 
1 2.30| 100.92 4:30 | 6.34 | 36.70) 0.290 
155 | Mouth of Sheep Corral Caton, Vir- | Dr. Auger - - | 68.81 13-62 3:92 PSs Si pe Bera Keath os 
ginia Mountains. 86:70 % ee se rae 
= 0.56 100.0 3-51 | 6.36 | 37.49) 0.263 
156 | Shoshone Falls- - - - - W. G. Mixter - | 70.30] 13:65 ee Pee Meee 2.36 8.10 | 37.49| 0.279 
5 | 37-49 6.36 49 Sa 
! 


TRACHYTES. 605 


cerned by the naked eye. Professor Zirkel finds it to be made up of a fine 
crystalline mixture of feldspar, impregnated with augite dust and minute 
crystals of pale, brownish-yellow augite. A glass base and olivine are 
entirely wanting. Here, therefore, are three distinct periods of trachytic 
eruption, all, however, characterized by the presence of augite. It is 
interesting that the presence of augite and of triclinic feldspar in these 
fine-grained gray trachytes should produce the appearance of basalt. But 
this basaltic habit is even more prominently developed in certain other black 
trachytes of this region, particularly those which form the low hills between 
Wadsworth and Sheep Corral Canon. These occurrences, although not in 
immediate connection with the foregoing augite-trachytes, doubtless repre- 
sent the most extremely augitic portions of the same general ejection, and 
probably its most recent effort. They are black and dark brown, with a 
highly vitreous lustre, breaking exactly like the half glassy basalts, and 
were it not for the large sanidin crystals evident even to the naked eye, 
might readily, in the absence of microscopic examination, pass for an 
augite-andesite or even for a basalt. The microscope shows them to be 
made up of predominating sanidin, pale-green augite, a little plagioclase, 
some brilliant brown hornblende, and an occasional flake of dark brown 
mica; the groundmass consisting of colorless crystals of sanidin and augite, 
embedded in an abundant colorless glass base. A similar black trachyte 
cuts the white acidic rocks just north of Truckee Ferry in sharp dikes. 

Petrographically, these rocks are still trachytes, owing to the pre- 
dominance of orthoclastic over plagioclastic feldspars. In habitus they 
are actually basaltic, and in a geological sense might, but for their age, as 
suggested in Volume II., be considered as basalts with the olivine left out, 
in which a portion of the plagioclase was replaced by sanidin. 'The heavy 
exposures of trachyte at the head of Sheep Corral Canon are of character- 
istic sanidin varieties, the groundmass consisting of sanidin microlites 
cemented by black grains and carrying in the interstices a varying 
amount of glass. The larger secreted minerals are heavy blocks of sani- 
din, reaching sometimes three fourths of an inch in dimensions, a few bril- 


liantly stratified plagioclases, and large rude brown biotites. 


SECTION IV. 
RHYOLITES. 


The distribution of rhyolite is even more irregular than that of the 
foregoing family. In the region of the Rocky Mountains it accompanies 
the two great trachytic localities, but with the exception of the small, 
insignificant exposure on Bear River, in Wyoming, there are no rhyolites 
between the Rocky Mountains and the western side of Great Salt Lake 
Desert. From the meridian of 114° westward to the borders of California, 
however, rhyolitic rocks cover a greater area than any other of the volcanic 
family. Taken as a whole, rhyolite is superficially the predominating 
volcanic rock of the Fortieth Parallel field, and considerably exceeds the 
basalts, which rank next in territorial area. These two families, at once 
the most acidic and most basic, cover together ten times as many square 
miles as all the rest of the volcanic series combined. The rhyolites, as 
will be seen from certain Nevada localities, are post-Miocene, and the 
earliest eruptions are contemporaneous with the first Pliocene beds. The 
line of demarkation between the fresh-water Miocene and Pliocene forma- 
tions of Nevada and Oregon is exceedingly sharp. The Miocene strata are 
all disturbed, and frequently thrown into high angle. The extravasation 
of rhyolites was a feature of the orographical disturbance which followed the 
dislocation of the Miocene rocks, and the earliest accumulations of Pliocene 
contain products of the first rhyolitic eruption. In many places, however, 
notably northeastern Nevada, the outpourings of rhyolite continued well 
into the Pliocene period; and a vast amount of the Humboldt Pliocene of 
that region is made of the acidic ejecta of the rhyolitic period laid down in 
the fresh-water lakes as local tuff-beds. As the trachytic eruptions form 
the characteristic volcanic feature of the late Miocene, so the rhyolitic were 
characteristic of the opening of the Pliocene, and extended over perhaps 
the first third of the Pliocene epoch. 

A world-wide observation as to the location of Tertiary eruptions is, the 
frequency of their appearing at the angles of powerful flexures or dislocations 

606 


RHYOLITES. 607 


of earlier rock masses. The most eastern exposure of rhyolite is no excep- 
tion to this rule. Mount Richthofen stands at the point of meeting of two 
distinct trends of the Rocky Mountain Archean rocks. The Medicine Bow 
trend, which for 100 miles has been southeast, suddenly bends at Mount 
Richthofen into a meridional strike. Within the angle of this sharp flexure 
occurs an extensive outpouring of rhyolitic rocks. They flank the beds of 
the Archean slope for twenty-five miles, rising highest against the base of 
Mount Richthofen, where the volume of the eruption was greatest. Toward 
the basin of the Park the rhyolites descend in broad tables, separated by the 
valleys of the upper branches of the Platte One particular ridge which 
extends out to the middle of the Park can hardly be considered as a rhyo- 
lite stream. Itis probably the overflow of a fissure extending out through 
the Cretaceous rocks. This is rendered probable by the inclination of the 
beds to the south instead of to the northwest, or in the direction of the rhyo- 
litic body. The greater part of the high ridges and upper slopes of the 
rhyolite are covered by dense forests, and the outcrops show no very char- 
acteristic forms. They overlie the Cretaceous, probably the trachytes, and 
are in turn overlaid by the Pliocene lacustrine North Park strata. In the 
region of Mount Richthofen the light granitoid Archean rocks are deluged 
by the dark-colored rhyolites. The groundmass is a fine-grained mingling 
of fragmentary crystals of sanidin and crystalline grains of dark quartz, the 
color varying through purple, gray, red, and brown, but usually of dark 
hues. Large single grains of dark, pellucid quartz surrounded by sphzxro- 
litic matter, black, shining hornblendes, and large, fractured sanidins are 
the only crystalline secretions in the main rock. 

The rocks at the head of Sioux Creek are somewhat of an exception 
to this rule, the groundmass being the usual light color, with more of a fel- 
sitic homogeneity, the included feldspars and quartzes being larger than 
the prevailing type of the neighborhood. Besides the sanidin, there are true 
orthoclase crystals. One of the most curious features about a locality of 
varied volcanic rocks is the tendency of some one or more peculiar forms 
to reappear in ejecta of entirely different chemistry and widely separated 
dates. Here, in the neighborhood of that peculiar rock which shares the 
characteristics of granite-porphyry and trachyte, and whose remarkable 


608 SYSTEMATIC GEOLOGY. 


feature is the highly modified orthoclases, occurs a long-subsequent rhyolite 
also reproducing, though in less perfect crystalline state, the more opaque, 
ancient form of orthoclase. In these light rhyolites hornblende is very 
abundant, though never occurring in highly defined or large crystals. 

About ten miles north of Evanston, in the neighborhood of some 
limited Cretaceous exposures, but otherwise altogether surrounded by the 
nearly horizontal beds of the Vermilion Creek Eocene group, is a small 
outcrop of rhyolite, far removed from all other volcanic rocks. It is a 
fine-grained, pumiceous, lavender-colored rock, the groundmass being the 
ordinary intimate mixture of sanidin and quartz, in which are interspersed 
lamin of very dark and of brownish mica. The outcrop is only of im- 
portance from its wide separation from other volcanic fields, the nearest 
eruptions being some miles down Bear River in the neighborhood of its 
great bend. 

West of the Wahsatch the rhyolites first make their appearance along 

the southern terminations of the spurs of the Raft River Mountains, and in 
isolated buttes rising to moderate elevations above the desert south of the 
range. Several are so small as to pass unnoted on the map. The most 
important are those of Desert Buttes, about four miles north of the railroad, 
and Owl Butte, about seven miles to the south. The rhyolite of Desert 
Buttes, near the old wagon road west of the southwest point of the Raft 
tiver Mountains, is a dense, compact rock. Macroscopically it is homo- 
geneous, and has a sharp, angular fracture, varying in color from light, 
warm gray to salmon. It contains rough spherolites and lithophyses, and 
is reticulated by fine veinlets of translucent chalcedony. Through the 
groundmass are brilliant, colorless quartzes and sanidins, the former abound- 
ing in inclusions of glass, and also filling the interstices of the groundmass. 
Certain of the druses carry tridymite. This eruption is doubtless connected 
with the line of rhyolitic buttes east of the northern termination of Ombe 
Range, as well as with the sheet of rhyolite which underlies the basalt and 
forms the northernmost rock of the Ombe. 

Along the eastern edge of the northern foot-hills of the range southwest 
of Lucin, for about four miles, the hills are made up of rounded rhyolitic 
masses, which to the north give way to Pliocene beds that are themselves 


RHYOLITES. 609 


almost altogether made up of rhyolitic tuff. A few miles southeast of Te- 
coma, at the edge of the field of basalt, outcrops a second isolated body of 
rhyolite. This is doubtless connected underneath the basalt with those on 
the eastern side of the range, the basic rocks having clearly overflowed the 
eroded hills of rhyolite. A rhyolitic butte at the extreme northern point 
near Lucin is a broad, flat-topped hill with steeply sloping sides, the summit 
300 or 400 feet above the valley. The rocks of this group are character- 
istically reddish-brown glass, carrying embedded sanidins and quartzes. A 
notable feature is the macroscopic inclusions of reddish glass in quartz, which 
in the hand specimens are very easily visible to the unaided eye. Zirkel* 
gives an interesting description of the microscopical structure of this rock— 
alternating layers of different-colored glass, which have been kneaded and 
squeezed together in confused positions. Some specimens show the glass 
drawn out into narrow bands and streaks; and although the prevailing 
shades of all the rocks are salmon, red, and deep, almost sienna colors, yet 
in places the glass pales out into an almost colorless condition. 

North of the railroad and north of this group of rhyolites, the Goose 
Creek Mountains, formed of the Upper Coal Measure group of limestones, 
are covered from base to base by a broad flow of rhyolite, which has been 
eroded off the southern limestone points of the range. The main central 
flow is a greenish-white, rough, trachytoid rhyolite, having only a few crys- 
tals of quartz and tabular feldspars—the latter often twins—scattered through 
the groundmass. The groundmass itself is one of those peculiar porcelane- 
ous products which reappear at various points in Nevada. Under the micro- 
scope it is seen to be a mixture of transparent, polarizing particles, and some 
dull-yellowish bodies, which are possibly glassy. On the hill slopes are 
various porphyritic varieties of the characteristic purple and red shales, full 
of macroscopical quartz and sanidins. In several specimens, representing 
a considerable area, the quartzes have excellent pyramidal terminations, a 
feature which is rare in the Nevada rhyolites, but frequently noticed in 
the dacites. In connection with these terminated quartzes, the groundmass 
is rich in fibrated sphzrolites having a sanidin crystal as the spheerolitic 
nucleus. Tridymite occurs here in connection with the sphzerolites, as it 


“United States Geological Exploration of the Fortieth Parallel, Vol. VI, page 198. 
39 K 


610 SYSTEMATIC GEOLOGY. 


does at Ombe Buttes. Along the eastern slopes of the mountains the 
lithoid varieties of rhyolite give way to half glassy and pearlitic forms. A 
prominent type of these is a gray, porphyritic mass containing imperfect 
dihexahedrons of quartz, sanidin, biotite, augite, hornblende, and mag- 
netite, all embedded in a microlitic glass. Another form is a pale yel- 
lowish-gray glass, in which are quartzes, sanidins, and microlitic products 
of devitrification, the latter showing by their arrangement the fluidal lines 
characteristic of the rhyolite group. The association of porcelaneous rhyo- 
lites with rhyolites of a pearlitic groundmass rich in products of devitrifi- 
cation, and including sanidin and quartz which are themselves rich in glass 
inclusions, again recurs in western Nevada in Montezuma Range. 

The westernmost rhyolites of the Goose Creek Hills pass under the 
Quaternary of Passage Creek. On the western side of this valley, oceupy- 
ing the northern hills of the Toano group, a body of rhyolite defines the 
western edge of Desert Gap. The hills rise 800 or 900 feet; but we have 
no means of judging the volume of the rhyolites, since they clearly overlie 
lofty spurs of Upper Coal Measure limestone. The rock has a purplish- 
gray color, and is noticeable for rough, drusy cavities lined with minute 
crystals of quartz. The groundmass, which is composed of stripes and 
bands of glass of two distinct colors, encloses the druses, and also the 
grains of quartz and small crystals of feldspar. More than ordinarily large 
lithophyses are seen. 

Unimportant masses of rhyolite occur in the Fountain Head Hills and 
on the eastern base of the Tucubits Mountains in Holmes Creek Valley, the 
latter accompanied by dark obsidian. Rhyolites wrap around the southern 
end of the Tucubits Mountains south of Tulaseo Peak, from which flow 
our specimens show a dark-brownish, rather loosely compacted, highly 
erystalline rock, with macroscopical quartz, sanidins, and biotites in a 
groundmass carrying a great deal of glass. Farther up the range, de- 
tached from the foot-hills, out of the Pliocene Tertiary rises a hill about 
1,000 feet high, called Forellen Butte, in which the rhyolite is a grayish- 
drab, felsitic mass, carrying large crystals of sanidin and quartz, the whole 
being intimately brecciated, and the fragments themselves containing bits 
of an anterior breccia. It is distinctly an eruptive breccia, noticeable for 


RHYOLITES. 611 


the sharply angular character of the shattered fragments, both of the in- 
cluded hornstone-like rhyolite and of the broken crystals. The relation of 
the rhyolites, on both sides of the Tucubits, to the geology of the region is 
very simple. The range itself is a dislocated block of deep-lying Palaeozoic 
rocks which have been brought to the surface by a sharp, powerful, local 
uplift, and the rhyolites appear along the lines of fracture which define the 
limits of the dislocated blocks. 

A very important region of rhyolites is that lying southwest of the 
westernmost point of Salt Lake Desert, embracing the Wachoe Moun- 
tains, the little chain of buttes in the desert directly west, and the broad 
field which overflows the northern end of the Schell Creek Mountains and 
Antelope Hills. East of this, on the elevation which marks the southern 
prolongation of Gosiute Range, are also isolated tabular hills of rhyolite ; 
and at the lower end of Deep Creek Valley, where the waters flow out 
upon the desert, is an interesting group of detached rhyolitic hills. 

It is a noteworthy fact that in general Salt Lake Desert itself is so 
free from eruptive rocks, while as soon as the hill country to the west be- 
gins to rise toward the high plateau of central Nevada, every range is more 
or less broken through by voleani¢ outbursts, and in general the frequency 
and complexity of volcanic localities increases from Salt Lake Desert west- 
ward. In the region of the Wachoe, Schell Creek, and Gosiute mountains 
the rhyolites all come to the surface in the neighborhood of Lower Coal 
Measure limestones. In the Wachoe it is true they have flowed around the 
nucleal mass of Archzean granite; and in Kinsley District they are con- 
tiguous to Archzan granites and porphyries. Limited masses of andesite 
appear on the Gosiute and at the Wachoe; but in general the rhyolites 
come to the surface over what are the depressed summits of folded Palzeo- 
zoic limestone ranges, which have been more or less dislocated and thrown 
down below the level of the neighboring ranges. Antelope Hills and the 
Schell Creek and Wachoe mountains show the subsided top of a range 
which to the south rises to quite lofty heights ; and Gosiute Range—which 
from the region of Toano to the south has been a defined, elevated moun- 
tain chain—south of Mount Pisgah suddenly drops out of view; its axis, 
however, is defined by outflows of andesite and rhyolite. It is, therefore, 


612 SYSTEMATIC GEOLOGY. 


the very reverse of the Tucubits region. There the mountain block of 
stratified rocks has been lifted above its natural level, and the rhyolites 
have broken out upon the flanks of the range, following the side fissures. 
In the case of the southern region, the ranges have gone down and the 
rhyolites have closed over their summits, covering the whole breadth of the 
mountain group. The Goose Creek Hills represent a third type of geologi- 
cal occurrence. With no particular depression or elevation of the range 
itself, the whole block has been riven with fissures, and the rhyolites have 
poured out, gradually accumulating over the elevated summits and spread- 
ing themselves out with a viscous flow down the flanks. The following 
are some of the varieties of rhyolite of the Wachoe region : 

At Spring Cafion, Wachoe Mountains, occurs a hornstone-like,.green- 
ish-drab rock, including in the groundmass, granules of quartz and crystals 
of feldspar, but no mica; also angular porcelaneous fragments entangled in 
the matrix, which represent probably the dcébris of some subterraneously 
solidified rhyolite quite devoid of crystalline secretions. The groundmass, 
whose devitrification the microscope shows to yield both axial and central 
fibrations, is not only devitrified, but in some places decomposed, resulting 
in soft green spots, in the centre of which are sometimes earthy nuclei of 
carbonate of lime which readily effervesce with acids. 

Another variety, also from Spring Canon, is a brick-red, porphyritic 
rock containing white crystals of sanidin and prisms of hornblende, but no 
mica. Near the mouth of the canon is a granitoid variety approaching 
neyadite, carrying abundant hornblende and feldspar, but showing no free 
quartz or mica. The sparing groundmass is of a leaden-gray color, richly 
microlitic under the microscope. The hornblendes are dark brown. 'There 
is also pale-yellowish augite, which the microscope shows to be penetrated 
with apatite prisms. All the crystalline inclusions except hornblende con- 
tain glass inclusions of unusual size. 

Along the northern edge of the group, north of Spring Canon, the rhyo- 
lites come directly in contact with the granite, and are also seen to overlie 
the andesites in immediate contact. This is one of the most admirable 
localities in our area for observing the contact between these two rocks, 
and here the rhyolite is unmistakably seen in direct superposition upon the 


RHYOLITES. 613 


original andesitic slopes. All these northern hills are exceedingly rich in 
varieties of rhyolite, both in color and texture. The rocks vary from mile 
to mile through a constant succession of changes. They have a variety of 
colors, shading through yellow, purple, black, white, and cream-color, and 
show all degrees of coarseness. For the most part they consist of a micro- 
felsitic groundmass rich in glass, carrying secreted crystals of varying size 
composed of sanidin, plagioclase, quartz, and hornblende, with occasional 
augites. There are also true pumices, besides glassy and half glassy rhy- 
olites of brilliant tint. A characteristic form of the latter has a bright red 
groundmass in which are blood-red zones of porcelaneous substance which 
enclose granules of pellucid quartz and water-clear, cracked sanidins. This 
parallel banding of material gives an almost stratified appearance to the 
rock. The quartz of this particular variety is noticeable for the liquid in- 
clusions with movable bubbles which were detected in it by Zirkel. 

From the broad mass of Antelope Hills an interesting type was col- 
lected adjoining the marble hills on the south. It is a porphyritie variety 
of a bright, brick-red color, with compact, white feldspars, quartz, and horn- 
blende, the groundmass being essentially felsitic. The quartz, which at 
times is seen grouped in lenticular masses, also lines the interior of druses 
with brilliant crystals. 

On the ridge south of Leach Springs is a rhyolite showing the charac- 
teristic fluidal structure of the group, the fine microlitic groundmass con- 
taining large hornblendes, tridymite, and apatite. 

Properly included in this region are two masses of rhyolite, one to the 
north of Mahogany Peak, in the northern end of Egan Range. Here, as 
may be seen from the lower section at the bottom of Map IIL., the rhyolite 
bursts through a slightly faulted anticlinal, occupying an axial position ex- 
tending about six miles north-and-south. 

Again, through the limestone of Ruby group, at an interesting locality 
called by Mr. Emmons ‘‘the Beehives,” is an eruption of a white, rhyolitic 
tuff. This, like the Egan Mountain outburst, comes through a fold of the 
Wahsatch limestone. Although a characteristic tuff, it was probably erupted 
in a muddy condition, its ejection accompanied by a great deal of water, 
but there are no signs of the tuff having been rearranged in aqueous strata. 


614 SYSTEMATIC GEOLOGY. 


The outcrops are interesting high knolls, whose surface is covered with pits 
from which the once included blocks of solid white rhyolite have dropped 
out, leaving a marking like the top of a thimble. The tuff is light-gray 
and creamy, with fine white spots of kaolinized feldspar, and dotted 
with hexagonal plates of biotite and small crystalline fragments of quartz. 
The unaltered fragments contain, in a drab, felsitic groundmass, crystals of 
sanidin, fine flakes of biotite, hornblende, and large pellucid quartzes. 

The northern part of Humboldt Range has suffered severe dislocation 
and fissuring. A prominent line of dislocation is Sacred Pass, which crosses 
the range obliquely ina northwest-and-southeast direction. Near the west- 
ern base of the range, at one end of this depression, is an outburst of pecul- 
iar earthy, green rhyolite. The valley of Clover Camion also has at its head 
a disturbed region which is walled in eastward by a sort of thumb of 
Archean rocks, which projects from the main ridge at Clover Peak. Here, 
in the angle between the thumb and the hand, as it were, is an outburst of 
very peculiar rhyolite. It is as black as a basalt, the groundmass being a 
dark-brown, nearly black glass, rich in feldspathic and augitic microlites, 
and carrying as macroscopic secretions sanidin, plagioclase, augite, and free 
quartz. The quartzes are of a brilliant olive-green, and at the first glance 
resemble the cracked grains of olivine in certain of the basalts that are rich 
in that mineral. The cracks, which traverse the quartzes in every direc- 
tion, are filled with and defined by a dark-yellow, earthy ochre, besides 
which there are no inclusions. Both feldspars, however, are surcharged 
with half glassy inclusions. This is another interesting instance of the asso- 
ciation of augite and quartz, the two minerals of all others characteristic of 
the two opposing chemical types of volcanic rock. 

The rhyolite at the northwest end of Sacred Pass breaks through 
and overflows the fossiliferous limestone of the Lower Coal Measures, and 
also abuts against the Archean foot-hills to the north of the pass, and is 
overlaid by the horizontal Pliocenes of Humboldt Valley. This rock is a 
pale-green and pale-olive rhyolitic tuff, inclining to a chalky whiteness in 
some specimens. It has a little free quartz and sanidin, in a base which 
has suffered globulitic devitrifieation. Some of the tuff is fine-grained and 


compact, showing no macroscopical secretions. Although a large part of the 


RHYOLITES. 615 


feldspars are kaolinized, there is no indication of stratification-planes or 
other proof of its having been laid down in water. 

Decidedly the most remarkable volcanic feature in the whole field of 
this Exploration is the great train of rhyolite ranges forming a system 
having a northeast-and-southwest trend, and occupying Augusta, Fish Creek, 
Shoshone, Toyabe, Cortez, Seetoya, and parts of Pinon ranges and the 
Mallard Hills, and extending in the direction of the trend both north and 
south of our area of exploration. Here is a group of half a dozen ranges, 
of which the predominating rock is rhyolite, the whole constituting a belt 
explored by us for over 200 miles in length and from 45 to 80 miles in breadth. 
The greatest of the orographical features of the far West is Sierra Nevada 
Range, and at the period of the rhyolitic ejections a series of outflows fol- 
lowed closely the axis of that long line of elevation. In this great middle- 
Nevada chain of rhyolites the trend is almost exactly perpendicular to that 
of the Sierra Nevada, a relation which has its origin in the most impressive 
geological events of which we have any record in the whole West, namely, 
the great series of mountain folds which occurred at the close of the Jurassic 
age, defining the strike of the Sierra Nevada and the series of northeast- 
and-southwest ranges in Nevada, whose trend approaches a perpendicular 
to that of the Sierras. The great central-Nevada rhyolite belt has another 
connection which it is interesting to note here. It lies along the western 
margin of the exposure of Palaeozoic rocks. Beyond this chain of rhyo- 
lites the Palzeozoic series are wanting, and the Triassic and Jurassic rocks 
rest directly on an Archzean foundation. As was seen in a previous 
chapter, between the area of Paleozoic and Mesozoic rocks at the close of 
the Carboniferous a tremendous fault occurred here. The region of that 
enormous dislocation which had been subsequently thrown into folds at 
the close of the Jurassic period has given vent to the vast voleanic out- 
flows of the Tertiary. A glance at the analytical map of the Tertiary 
volcanic rocks at the close of this chapter will suffice to demonstrate the 
importance of the belt here noticed. 

The Mallard Hills, north of Humboldt River, between the meridians 
of 115° 15’ and 115° 45’, are altogether made up of rhyolitic flows; and 
with the exception of the andesites of Egyptian Canon are surrounded by 


616 SYSTEMATIC GEOLOGY. 


horizontal Pliocene beds. The highest points of the hills rise about 2,000 
feet above the surrounding Tertiary valleys, and the general configuration 
of the surface is that of broad ridges gently sloping from a culminating 
central region. There is nothing crater-form about the middle elevation. 
Like many rhyolites, this bears abundant evidence of true fluidity at the 
period of ejection. Structurally, the Mallard Hills occupy a position analo- 
gous to that of the Wachoe and Schell Creek mountains before described. 
Elko and River ranges, which have a northeast trend, are suddenly 
broken off, the continuity of their Palaeozoic uplift is lost, and the northern 
continuation depressed to an unknown depth. Over this gulf (which is 
clearly proved by the low altitudes from Bone Valley southeastward through 
Egyptian Canon in a line to Deeth Station) have flowed the eruptions of 
rhyolites, the whole depressed region building up to a height even superior 
to the normal altitude of the Paleozoic uplifts. Several petrographical 
varieties have been observed among these rhyolites. That from Deer 
Canon, on the northeast point of the hills, has the habit of splitting into 
thin lamine, from half an inch to an inch in thickness, precisely like some 
of the Elk Head quartziferous trachytes. The rock consists of a light lav- 
ender and gray felsitic groundmass, carrying fairly defined, impure sanidins 
and large rounded globules of quartz the size of a pea, having the character- 
istic interior net-work of cracks and an exterior ring which is a granular 
modification of the groundmass. Neither among the crystalline secretions 
nor in the finer elements of the groundmass is there any biotite or horn- 
blende. The central summit of the group is composed of a rock of similar 
type, often showing the same tendency to split into lamin. The general 
color of the type varies through shades of brownish red and dull, pure 
red. The groundmass, which has a somewhat trachytic appearance, 
under the microscope proves to be highly spheerolitic. Well developed 
sanidins and large, cracked globules of quartz are present in the ground- 
mass, but there is neither mica nor hornblende. The rock is of varying 
compactness, sometimes occurring in exceedingly porous, almost scoriaceous 
forms, the cavities being lined with botryoidal secretions of chaleedony 
and dark-brown, nearly black glass. The northern end of this group of 


mountains, on the watershed of Snake River, yields some pure-white por- 


RHYOLITES. 617 


celaneous rhyolite, with a remarkable conchoidal fracture and a vitreous 
lustre, 

Below the andesite mass of Egyptian Canon, rhyolitic spurs close in 
upon either side of the river, showing purplish porphyritic types which do 
not differ mineralogically from others of the group. So, too, along the 
eastern slopes of Bone Valley, modifications of the main type were col- 
lected. At the very southern end of the group, overlying the quartzites at 
Peko Peak, is a dull-gray rhyolite, also devoid of hornblende and biotite, 
but closely resembling some of the older felsites. It contains chips and 
fragments of chalcedony, but the microscope shows it to contain an enor- 
mous amount of ferrite. 

The southwestward continuation of this group appears in a little 
isolated hill west of the North Fork of Humboldt River, completely sur- 
rounded by horizontal Pliocenes. It is very compact, almost earthy in tex- 
ture where decomposed, but where preserving its original characteristics is 
a white porcelain. It contains very minute but distinct crystals of quartz, 
which are chiefly smoky, a few feldspars, and hornblendes, the microscope 
adding biotite. 

Normal biotite-rhyolite occurs directly north of the river at Osino 
Canon. It is rich in crystalline ingredients, having almost the characteristic 
habit of nevadite, and contains sanidin, biotite, and quartz. 

A singular development of rhyolite is observed directly north of the 
coal mine near the mouth of Penn Canon, River Range. The main moun- 
tain slopes are here formed of quartzitic beds of middle Coal Measure age. 
The strata are mainly formed of a peculiar brecciated material, in which 
the larger part of the fragments are sharply angular, while others are sub- 
rounded. The rhyolites which overlie these spurs bear a singular likeness 
to the brecciated quartzites. They have an earthy, felsitic groundmass, 
in which are crowded angular fragments of a highly siliceous material, 
which cannot be distinguished from broken pieces of the neighboring 
impure quartzites. One may trace almost a continuous passage from these 
angular rhyolitic breccias to the angular quartzitic conglomerate. It is cer- 
tainly a very perplexing occurrence, and may possibly be accounted for by 


the invasion of a region of these shattered, angular quartzitic fragments by 


618 SYSTEMATIC GEOLOGY. 


an exceedingly fluid, porcelaneous rhyolite, there being just enough of the 
magma to permit a quasi flow. On the other hand, there is nothing abso- 
lutely characteristic in the included fragments of the rhyolitic breccias, and 
they themselves may be the deep subterraneous fragments of a solidified 
felsitic rhyolite, free from crystalline secretions, which was shattered in the 
depths and brought to the surface after the ordinary manner of breccia 
eruption, in which case the similarity of these fragments to the angular 
material of the neighboring quartzites would be simply accidental. I 
incline to the former view—that the fragments are identical; that in one case 
they are simply held together by the sedimentary cement; and that in the 
other they have been floated off in a small amount of eruptive matrix. 

Among the rhyolites of this locality are very interesting homogeneous 
felsitic passages, brilliantly striped and banded with an extraordinary array 
of colors—red, brown, and yellow alternating with gray, white, or pale 
lavender—the mass closely resembling some of the earlier clay-stones 
which were the clastic eruptions of felsite-porphyries. 

South of Osino Canon, with the exception of a small amount of 
quartzites which outcrop on the southern wall of the cut, the heights for 
eight or ten miles to the south, indeed the whole range from side to side, 
is occupied by an overflow of rhyolites which possibly represent but a 
thin sheet of material over the Paleozoic ridge. The most interesting 
feature of this rhyolite is certain breccias at the southern end of the 
group, which are composed of innumerable angular fragments of a fine- 
grained, compact, felsitic matter, carrying brilliantly clear quartz grains, 
the whole held together by a rhyolitic magma not very different from the 
fragments in character. Besides this, it is traversed by wandering veins 
of chalcedony to such an extent that often a quarter of the rock is made 
up of its milky, translucent material. There are no biotites or hornblendes, 
but with the white quartzes are well crystallized sanidins. 

Seetoya Range, south of the parallel of 41° 15’, is another of those 
ridges in which the original mountain mass has been depressed and its 
place filled with rhyolites. The granitic tops of Maggie and Nannie’s 
peaks, and the heavy limestone body around the former, are summits of 


the earlier range which have remained lifted above the rhyolitic flows. 


RHYOLITES. 619 


Jonnected with a part of this same eruption is the body of rhyolites 
on the western side of River Range, bordering upon Susan Creek. In the 
latter group of hills are two distinct types of rhyolite. The first, a 
light-gray tufaceous rock, not unlike that near Penn Caron, has a rather 
porous, earthy groundmass, containing scattered crystals of sanidin and 
quartz. An unaltered rhyolite of the same neighborhood shows a semi- 
vitreous, light-gray porcelaneous mass very poor in crystalline secretions, 
a few isolated grains of quartz being the only ones seen. North of the 
andesitic body, on the divide between Susan Creek and North Fork, is a 
dark-gray variety, having a brownish groundmass rich in ferritic needles, 
which contains a multitude of biotites and hornblendes, the latter of a pecul- 
iar rusty-red color. In this rock are contained innumerable balls about an 
inch in diameter which are made up of distinct feldspar, quartz, hornblende, 
and occasional biotites in a vitreous base. 

The Palaeozoic mass about the granite of Nannie’s Peak is completely 
surrounded by rhyolites, and an interesting dike, west of the peak, cuts 
through the limestones for eight or nine miles, showing a nearly continu- 
ous exposure. The weathered surfaces resemble older felsitic porphyries. 
The rock itself is a yellowish-gray felsitic groundmass, having a ragged, 
granitoid fracture, inclining sometimes to a greenish color, and passing 
gradually into a pearlitic, glassy modification, containing highly vitreous 
sanidins. Under the microscope this groundmass shows rudimentary 
spheerolites. The macroscopical secretions are large crystals of horn- 
blende and quartz, and a little biotite. 

Farther south, in the neighborhood of Maggie Peak, where the rhy- 
olites come in contact with granite-porphyries, they closely resemble them 
in petrographical habit, their compact, white, felsitic groundmass contain- 
ing only crystals of quartz and showing interesting botryoidal secretions 
of hyalite and opaline chalcedony. 

In the region of Pinon Pass, latitude 40° 15’, the eastern base of the 
mountains, as well as the lofty ridge northeast of Pinon Pass, is composed 
of rhyolite which has come to the surface through a fissure that was a 
southward prolongation of the line of break characterized by trachytes to 
the north. It is a light, earthy rhyolite of rather trachytic texture and 


620 SYSTEMATIC GEOLOGY. 


habit, the groundmass rich in ferrite, containing numerous large, finely 
formed dihexahedral quartz grains, some more or less earthy, kaolinized 
sanidin, and a high proportion of flakes of black biotite. With the excep- 
tion of the latter mineral, the crystalline secretions are not evenly distrib- 
uted through the groundmass, but are gathered in important accumulations 
or bunches, ten or fifteen large feldspar grains grouping themselves to- 
gether. In the whole series of rhyolitic outbursts examined, there is no 
rock which is at all comparable with this for the proportion of shining 
black biotite. The groundmass is singularly devoid of glass, and the whole 
habit of the rock is precisely like that of trachyte, with which species it 
might be classed but for the abundant presence in the groundmass of micro- 
crystalline quartz. 

Twelve miles farther south, also on the eastern base of the range, in 
contact with Devonian limestone, is a limited rhyolitic outflow without any 
important petrographical characteristics. 

South of Pine Nut Pass, where Pinon Range reaches the southern limit 
of our map, is a body of rhyolite (not within our area) which is of some 
petrographical importance. Its peculiarity is the groundmass, which has 
a highly developed crystalline-granular structure closely resembling the 
eranite-porphyries. In this respect it is only inferior, among American 
rhyolites thus far studied, to the nevadites of Lassen’s Butte, which are 
altogether made up of individualized crystalline secretions, held together 
by an exceedingly minute amount of nearly colorless glass base. Here 
the groundmass consists of pellucid quartz grains, more or less rounded 
crystals of feldspar, a little brown biotite, and ferrite grains. An interesting 
accessory mineral is pure, bright garnets measuring two tenths of a milli- 
metre in diameter. 

A noteworthy group of rhyolites is that exposed in the middle of 
Cortez Range, north of Cortez Peak, extending eight or ten miles north 
of Carlin Peaks, and embracing the broad voleanic outflow north of 
Palisade Canon, including also the flows south of Carlin which occupy the 
heights of a portion of Pinon Range. This is essentially one group. 
In the region of Carlin Peaks isolated summits of the earlier limestones 
show that this, like almost all the other rhyolitic bodies, was a pre- 


RHYOLITES. 621 


determined range. The same is true south of Cortez Peak, in Cortez 
Range, where the high masses of Paleozoic and granitic rocks form con- 
spicuous summits. The northern end of the Pinon also shows an elevated 
region of Palaeozoic rocks. It is in the intermediate depression, where the 
older ridge had suffered an unusual subsidence, that the great group of 
volcanic rocks—propylites, andesites, trachytes, rhyolites, and basalts—has 
burst out. 

At Carlin Peaks, in contact with the detached Paleozoic outcrops, the 
rhyolite forms high, table-topped mountains composed of the ordinary red 
porphyritic variety, similar rocks extending south to the head of Nannie’s 
Peak and covering the western part of the range in long slopes as far south 
as the Emigrant Road. These rhyolites, in passing southward, have more 
and more of a trachytic habit, but may be distinguished from the earlier 
trachytes by the abundant presence of free quartz. Near the Emigrant Road, 
the rhyolites are reddish-gray rocks containing no macroscopical inclusions 
except a few sanidins and plagioclases. A characteristic of the rock here is 
the occurrence of numerous small cavities lined with a light-gray crust 
made up of thin, variously colored layers of hyalitic material. 

Near the northern end of the Cluro Hills are rhyolites of peculiarly 
shaly habit, splitting into lamine only half an inch thick, the whole abun- 
dantly stained with iron oxyd. Fresh fractures show a compact, felsitic 
groundmass containing quartz and sanidin. 

The most interesting rhyolites of this group are those occupying the sum- 
mit of the range a few miles north of Cortez Peak. Here is a lofty ridge of 
rhyolites which descend very rapidly to the depressed plain on the west 
Deep canons scored through this mass show rough, tabular flows piled one 
upon another in rather trachytoid habit as regards their geognostical char- 
acteristics. This eruption skirted the western edge of the ridge in a narrow 
line, flanking the earlier volcanic rocks almost as far north as Palisade Canon. 
The general colors of the rhyolites of this group are buff, green, and purple, 
and they are largely composed of breccias, of which many of the included 
fragments are of delicate, apple-green color, having a general felsitic 
groundmass, including decomposed feldspars and numerous angular and 
rounded quartz granules, the latter having a peculiar botryoidal surface like 


622 SYSTEMATIC GEOLOGY. 


hyalite. The fragments vary from the size of a pea to that of a mustard- 
seed. The general material in which the green breccia fragments are em- 
bedded is a yellow and cream-colored rhyolite, the groundmass being in 
an imperfectly crystalline state, rich in ferrite, containing numerous feld- 
spars which are all more or less kaolinized, and quartz in beautiful dihexa- 
hedral crystals and sometimes in simple angular fragments. These quartzes 
are peculiarly surrounded by a fine siliceous glazing, so that the cavities 
out of which the quartz has fallen present a smooth varnished surface. 
There are also in the yellowish or purple groundmass of the including 
rhyolite, rounded quartz pellets with botryoidal surfaces like those of 
the included green fragments. 

With the exception of certain purely foreign fragments picked up along 
the walls between which the various volcanic eruptions came to the surface, 
such as fragments of limestone in trachyte or bits of Archwan granite in 
rhyolite, it is a common characteristic of all the breccias that the included 
fragments and the matrix which contains them are of identical material, the 
two usually showing the minutest petrographical identity. 

The dacites of Cortez region are breccias containing dacitic fragments, 
and the feldspars of both the included fragments and the matrix have 
suffered precisely the same form of decomposition, resulting, among other 
products, in a fine crystalline cover of calcite. Here in these rhyolites this 
very unusual form of distinct botryoidal surfaces of the quartz is common 
to the fragments and the matrix. 

The northern point of the Wahweah Mountains falls within our field 
of observation, and, like the southern termination of the same group, is 
characterized by the presence of a small outflow of rhyolite. It has a 
purplish-gray, crystalline groundmass, consisting of colorless quartz-parti- 
cles, feldspars, and macroscopical plates of bronze mica. The crystalline 
inclusions are large, fresh biotites, brown, smoky quartzes, and feldspars, 
of which a comparatively large number are plagioclases. 

The high northern body of Shoshone Range, culminating in Shoshone 
Peak, slopes to the southeast, throwing out long foot-hill ridges, which are 
overlaid by a broad zone of rhyolites that reappear east of Carico Lake on 
the northern slopes of Carico and Railroad peaks, the whole forming a 


RHYOLITES. 623 


distinct group only separated from each other by the shallow Quater- 
nary valley which carries the drainage of Carico Lake northward through 
Rocky Pass into Crescent Valley. The rhyolites of what may be called 
the Carico district are of two distinct types. The earliest outflows are 
white and creamy tuff-deposits, which are seen immediately west of Carico 
Lake, and in a canon about four miles north of the Jake, which leads 
out from the Shoshone Mountains. The groundmass is finely microcrys- 
talline, the only macroscopical secretions being sparing quartz, and feldspars 
which have undergone kaolinie decomposition. There is no biotite or 
hornblende. Although the rock shows few planes of stratification, it is 
probably a subaqueous eruption which poured out into a lake formerly 
occupying Carico and Crescent valleys. It bears a close resemblance to 
some of the Miocene trachytic tuffs found north of the Kawsoh Moun- 
tains. Here, however, there seems to be no admixture of foreign clastic 
material, the microscope showing the main mass to consist of fragments 
of a microcrystalline admixture of quartz and sanidin. It is characteristic 
of some of the finer-grained rhyolitic tuffs that they show no planes of 
stratification. The absence of plates of biotite or of tabular hornblendes, 
which in the act of sedimentation would lie flat, leaves the homogeneous 
material without any indications of bedding. Probably not over eighty 
feet of these tuffs are seen. They only appear at wide, irregular intervals, 
and may possibly be direct ejections of rhyolitic mud. They are, however, 
on pretty nearly a common level, and that is the sole indication of their 
having been rearranged by lake waters. Over these the whole border of 
the range shows a powerful outflow of purple porphyritic rhyolite, with a 
coarsely crystalline groundmass, carrying but a small proportion of glassy 
base, the crystalline secretions being very coarse and numerous. The gen- 
eral habit of the groundmass is rather trachytic and crumbling, and the 
secretions embrace broken crystals of sanidin, small plagioclases, large pel- 
lucid quartzes, and some biotite. It is not often that two more distinct 
types of rhyolite than these white tuffs and the dark purple variety are 
found thus contiguous. 

North of Railroad Peak the rhyolites reach an elevation of 1,500 or 
2,000 feet above the valley, presenting the general appearance of rugged 


624 SYSTEMATIC GEOLOGY. 


granitic hills. Here are numerous high conical and pinnacled forms with 
precipitous sides, but showing around their bases little disintegrated or 
earthy d¢bris. 

One of the most extensive single groups of rhyolite within our area is 
that which projects north from the Shoshone Mesa to the northern limits of 
our map, defining at the north the powerful line of Owyhee Bluffs, together 
with the broad plateaus which form its eastern and western prolongations. 
Here is a field of rhyolite, roughly triangular, extending about fifty miles 
from north to south, by forty miles from east to west. It consists chiefly 
of three elevated regions, each having a northeast trend: that of the Sho- 
shone Mesa itself, the ridge which separates Rock Creek from Squaw Val- 
ley, and the Owyhee Bluffs. The two depressions in this triangle are 
occupied by horizontal Pliocene beds. The interior drainage of the group 
passes through these two valleys, delivering the outflow through Rock 
Creek into the Humboldt. This entire field is surrounded by Quaternary 
plains, with the exception of a narrow isthmus which unites it with Cortez 
Range in the locality of Soldier Creek and Tuscarora. In the latter region, 
lifted above the rhyolites, are the detached outcrops of a quartzite range, 
the main rhyolitic field occupying a region west of the Cortez and north 
of the Shoshone. On the geological maps, it will be seen that the pow- 
erful Shoshone Ridge and the lofty Paleozoic mass of Battle Mountain 
drop down abruptly beneath the Humboldt Valley, and do not reap- 
pear to the north, the only elevation being the great rhyolitic field. This 
is but another instance of the frequent mode of occurrence of the rhyolites 
in regions of deep dislocation and depression. 

In the Tuscarora region, where the rhyolites have overflowed propylite 
and andesite, they are usually white varieties which show a great deal of 
kaolinic alteration, feldspars being the only crystals macroscopically visible, 
though the microscope shows minute altered biotite and hornblende, 
together with more or less quartz. On the foot-hills a few miles north of 
Tuscarora, the rhyolites are a dark, reddish-brown body, having the field 
habits of andesite, although composed exclusively of sanidin and remark- 
ably regular hexagons of biotite, together with a few granules of quartz in 
a dark, compact, felsitic matrix. 


tH YOLITES. 625 


South of Tuscarora, where the rhyolites overflow a body of augite- 
andesite and constitute the foot-hills along the southwestern portion of 
Independence Valley, is a white porphyritic variety, the felsitic ground- 
mass having suffered considerable kaolinic decomposition, and the erystal- 
line secretions consisting of biotite, quartz, and sanidin. . 

A white amorphous rhyolite extends up on the eastern slope of 
Mount Neva to its very summit, and covers considerable slopes toward 
Owyhee Valley. 

A rock to the west of Mount Neva, which overflows the base of the 
quartzitic hills, is of quite a different petrographical type. It is a dark- 
gray mass of pearlite occurring in rude columnar structure. A pale-gray 
color characterizes the glass base, which is rich in microlites of varied 
forms. The crystalline secretions, which are exceedingly numerous, are of 
sanidin, biotite, a little plagioclase, and considerable free quartz. 

The broad ridge of Owyhee Bluffs, culminating in Mount Rose, 7,949 
feet above sea-level, displays remarkably well the flowing structure from 
which the name “rhyolite” is derived. The mountain is made up of thin 
sheets of rhyolitic lava, often no more than one eighth of an inch thick. 
The mass has a compact felsitic matrix containing only quartz and sanidin. 
The surface of each of the fine rhyolitic layers is coated with a dull-red 
earthy substance of ferritic nature, in which are entangled a few flattened 
erystals of sanidin. Among the flows on the southern slopes of this peak is 
an interesting rhyolite breccia. The included angular fragments, pink and 
red, are of rather earthy rhyolite, having sharp, rectangular outlines, with 
chips varying from half an inch to an inch in diameter. It is characteristic 
of all the enclosed fragments that they possess the fine parallel fluidal 
structure which gives them the aspect of woody fibre, so that the rock 
has much the appearance of inlaid woods, with the grain of different pieces 
running in different directions. 

In the lower foot-hills near Squaw Valley are dark pearlites, contain- 
ing quartz and sanidin, with microscopic augite. An interesting charac- 
teristic of this occurrence is the presence of inclusions formed of grouped 
granules of dark-green crystalline aggregations very rich in olivine, which 
is associated with tabular plagioclases and brown augite, the base rich in 

40 K 


626 SYSTEMATIC GEOLOGY. 


globulites and titanic iron. East of this, at Sunset Gap, near the western 
edge of Squaw Valley, is a similar pearlite, interbedded with a rhyolite of 
purely lithoid type, rich in erystals. The white porphyritic rhyolite, whose 
groundmass is essentially earthy, contains black hornblende, sanidin, 
quartz, and biotite, while the intercalated pearlitic beds are predominantly 
vitreous, but contain also, besides sanidin, a little plagioclase and augite. 

On the summit of the ridge which divides Squaw Valley from Rock 
Creek Valley are banded gray and red rhyolites, alternate bands consisting 
of the reddish felsitic groundmass and of aggregations of sanidin and 
quartz crystals, the layers of groundmass showing under the microscope an 
abundance of ferrite and spherolites. 

A noticeable variety of rhyolite occurs near Warm Springs, where 
the rhyolites west of Rock Creek Valley pass under the Quaternary of the 
Plains. It is pearl-gray, rich in small gray, glassy sanidins and large 
rounded quartz globules intricately cracked, besides which the microscope 
shows an unusual abundance of tridymite. 

Shoshone Mesa itself presents sharp cliffs to the south, east, and west, 
rising 2,000 to 2,400 feet above the surrounding plain. The lower foot-hills, 
extending perhaps half-way up the slope, display rhyolites which are over- 
laid above by a continuous field of basalt. These rhyolites are usually 
dark-purple and thinly bedded, composed of a groundmass which is rather 
microcrystalline than microfelsitic, showing little fibration except around 
the larger crystals It includes plagioclase, considerable apatite, quartz, 
and large crystals of sanidin. Associated with the last mentioned variety 
is a peculiar dark pearlite, rich in lithophyses an inch in diameter. In the 
black glassy matrix are abundant crystals of sanidin and quartz. In the 
immediate vicinity of the large lithophyses, the glass loses its dark color 
and is nearly white. The nuclei of some of the lithophyses are noticeable 
for central groups of quartzes and sanidins. The microscope adds biotite, 
hornblende, and augite to the list of crystalline secretions. Spheerolites 
an inch in diameter are richly distributed through the gray groundmass, 
which upon decomposition develop the well known concentric structure 
and in the most advanced stages reach the condition of lithophyses. 

About a mile back from the edge of the cliff, on the eastern side of the 


RHYOLITES. 627 


Mesa, a considerable hill rises above the level of the basalt field, which has 
a general semicircular shape, and suggests the broken outlines of a crater. 
The rock is the same pearl-colored rhyolite found at the western base of the 
hills near Warm Springs. It is less richly erystalline than the rhyolites 
farther down on the slope, and, like the other pearl-colored rhyolite, con- 
tains large amounts of tridymite. 

As a whole, therefore, this group displays three types of rhyolite: the 
pearl-gray variety, poor in crystalline secretions but rich in tridymite; the 
dark pearlites, which are characterized by more or less sphzerolites and their 
decomposed relics, the lithophyses, and usually more or less augite; and 
lastly the ordinary typical rhyolite, rich in crystals of sanidin, and cracked 
quartz granules, together with a little plagioclase and occasional biotite. 

Passing southward from Shoshone Peak, the lofty masses of sedi- 
mentary rock which have formed the upper portions of the range begin to 
disappear, and the continuation of the ridge is in great part made up of 
rhyolites. The deep pass through which Reese River flows, and which 
severs the range into distinct halves, shows but little of the sedimentary 
rocks in the cut, which is evidence that they are sunken relatively below 
the corresponding northern portions of the range. Here again, as we have 
seen previously, the rhyolites come to the surface where the rocks are 
comparatively depressed. 

The low ridge of the Mount Airy hills and the pass leading from Reese 
River Valley, near Jacobsville, to Lone Hill Valley, still further show that 
the main underlying body of Paleozoic rocks has gone down. The ranges 
of this immediate region have been dislocated into irregular blocks, these 
blocks or sections have been left at a variety of altitudes, and wherever the 
bodies have subsided lowest, there the lines of fracture seem to offer the 
easiest exit to the volcanic materials. As a consequence, the rhyolite has 
built up enormous piles. Were it not for an occasional deep pass through 
the range, exposing the full thickness of the rhyolite, we might suppose 
that the underlying skeleton of Paleozoic rocks was continuous, and at a 
comparatively high level; and that the rhyolites were mere thin covers 
which outflowed over them. But in view of the profound passes which 
cut the ranges sharply through, showing no stratified rocks, and when we 


628 SYSTEMATIC GEOLOGY. 


further consider the abrupt terminations of the blocks into which the Pale- 
ozoic ranges have been broken, suchas occur north of the Dome in Toyabe 
Range and north of Shoshone Peak in Shoshone Range, it is evident that 
the great rhyolitic regions, with their enormous massive eruptions, do 
really represent areas where the Paleeozoic blocks have gone down. Cer- 
tain of the valleys of this great rhyolitic region are covered with a thin 
eroup of Quaternary and Lower Quaternary formations superposed upon 
the rhyolitic slopes. Others, as those seen about the margin of the upturned 
Miocene, are not underlaid by rhyolites, but the volcanic rocks are confined 
to the actual mountain ranges. The prevailing petrological type in Sho- 
shone Range north of Reese River Canon, especially in the neighborhood 
of Hot Springs, is a variegated rock passing from purple and gray into 
reddish, lilac, and rusty-buff colors. The groundmass is microfelsitic, show- 
ing under the microscope a characteristic rhyolitic habit. The macroscopic 
minerals are sanidins, a few plagioclases, large abundant quartzes, and rare, 
partially decomposed biotites. 

Among the most interesting forms are those which skirt the foot-hills 
of the Ravenswood mass, where they descend to the canon through which 
Reese River traverses the range. Here is exposed a series of rhyolitic 
breecias mostly purplish-gray and bluish-gray, ordinarily without free 
quartz, and of a loose, almost tuff-like texture. Among the lower members, 
and especially those of lighter colors, the orthoclases are decidedly kaolin- 
ized, and the material is probably one of those eruptions of mixed volcanic 
mud and breccia. This is not the sole instance in which the lower expo- 
sures, indicating earlier eruptions of rhyolite, are either breccias or tuffs. 
Not a little of the rhyolites poured into and was ejected under the fresh- 
water lakes which covered the Nevada lowlands during the Pliocene age. 
The breccias are altogether made up of rhyolitic material. The fragments 
which are enclosed in the looser and more friable matrix are uniformly 
of rhyolite. Some of these included fragments are themselves made 
up of a rhyolitic breccia, the fine felsitie material of the blocks being 
cemented by a still finer-grained microfelsitic groundmass. Among the 
gray, earthy, kaolinized breccias are frequent brilliant, undecomposed biotite 
crystals. 


RHYOULITES. 629 


Interesting rhyolite breccias occur along the eastern base of the Ravens- 
wood mass, resembling the compact rhyolitie tuffs found near Elko and 
the Penn Canon coal mines. The included fragments are in general of a 
finer felsitic paste, containing granules of quartz and occasional crystals 
of feldspar. They are always sharply angular, and are cemented together 
by an almost chalcedonic magma. Associated with these are equally fine 
grayish-purple, hornstone-like varieties, of which the finer included frag- 
ments are used for flints by the Indians. The surface is largely covered 
with chips in which the proportion of silica must run considerably above 
80 per cent. 

West of the Archzean body that forms the central core of the southern 
portion of Shoshone Range are red and purple rhyolites which are highly 
crystalline, containing fine granules of quartz in great abundance, large 
glassy sanidins, and occasional micas. Along the western skirts of the 
range are the same ashy-gray volcanic tuffs and cream-colored beds which 
have been previously described in the region of Carico Lake. This is evi- 
dently where the western margin of the rhyolite flows came to the surface 
under the fresh waters which formerly occupied Lone Hill Valley. 

Farther south, the western flanks of a little group of hills known as 
Jacob’s Promontory are formed of dark-gray rhyolites having a marked 
resemblance to the neighboring andesites. This resemblance also appears 
in the microscopic examination, since the groundmass is a felt-like aggre- 
gation of microlites. They are, however, of monoclinic feldspar, and the 
larger secretions are also of sanidin. Besides these, free quartz and very 
perfect dark-green hornblendes occur, the latter having the dark border 
characteristic of the andesite family. This is another example of a fact 
frequently noticed by Messrs. Hague and Emmons and myself, namely, 
that in nearly all cases where several volcanic species occur together, each 
one possesses some leaning toward the types of the others; as at Washoe 
certain of the plagioclase-trachytes, andesites, and propylites bear a strik- 
ing resemblance in the relation of their secreted minerals to the ground- 
masses, by which the resulting porphyries are puzzlingly similar. 

The hills in the neighborhood of Mount Airy illustrate again the sue- 


cession of gray, earthy tufis, breccias, and solid crystalline rhyolitic 


630 SYSTEMATIC GEOLOGY. 


flows. At the bottom are mauve, yellow, and gray tuffs, containing a few 
particles of feldspar more or less kaolinized, bits of black glass, and occa- 
sional but rare crystals of biotite. Above these are hard, brittle, felsitic 
rhyolite breccias, of which the fragments are always angular, and above 
is a series of reddish rocks characterized by abundant quartz and sanidin, 
with very little mica. Much of the quartz is smoky or wine-colored, and 
is surrounded by a peculiar opaque, white, earthy coating. This succes- 
sion of rhyolites, having a total thickness of 300 or 400 feet, is arranged 
in beds with a distinct inclination to the east. It is a rule that nearly all 
rhyolites observed in ranges of any considerable altitude, and wherever 
the bedding is at all appreciable, are seen to dip toward the nearest plain. 
Not unfrequently the edges of these beds appear in a rather sharp escarp- 
ment, as if a vertical fault had cut them. 

North of Mount Airy a series of hills connects Shoshone Range 
with the Desatoya group. They are entirely made up of rhyolites, 
with a distinct bedding which inclines toward the west. They belong 
therefore to the system of Shoshone outflows, and are made up of 
alternating beds of dark, pearlitic rhyolite, almost obsidian, and earthy, 
crumbling varieties poor in large crystals. The glassy beds are from ten 
to twenty feet thick. Such alternations of distinctly glassy and thoroughly 
crystalline material are not the least difficult of the problems of volcanic 
geology. In this case, a few sanidin, quartz, and plagioclase crystals 
which occur in the glassy mass contain abundant microscopic inclusions 
of the main glass magma, while the crystals of the less glassy forms are 
decidedly poorer in glass inclusions. Through the whole range of glassy, 
half glassy, and distinctly crystallized rocks, the proportion of glass inclu- 
sions in the crystals bears a pretty direct relation to the amount of glass 
base present in the rock. 

That portion of the Desatoya Mountains within our field consists of a 
central elevation of Triassic rocks accompanied by ejections of diorite, 
this limited body being entirely surrounded by, and all the rest of the range 
being completely submerged beneath, wide fields of rhyolite. In direct 
proximity to the diorite, the rhyolites occur as a light-green breccia, con- 


taining much half glassy material approaching pumice in texture. With 


RHYOLITES. 631 


this is associated another type, also a breccia, which has large crys- 
tals of biotite and quartz, a yellowish-gray hornstone-like groundmass, 
containing biotite and apatite, and large, well developed sphrolites, be- 
tween which are axially fibrous felsitie bands. To the south of these 
breccias is a red, more compact rhyolite, containing blocks and fragments 
of the light-greenish rhyolite above mentioned. Here are seen the same 
large dark-yellow spherolites. Along the western foot-hills of the groups 
are dark-red porphyritie varieties, noticeable for the large proportion of 
apatite they contain. On the other hand, those along the eastern foot-hills 
are noticeable for their abundance of limpid quartz full of remarkably 
large glass inclusions. 

The most satisfactory display of rhyolites in the Desatoya Mountains 
may be obtained at New Pass, which opens a walled gorge across the 
group of hills. Here are displayed not less than 1,000 feet in thickness of 
rhyolites. In the middle of the pass the type is a breecia, white and green 
below, with pinkish and reddish colors above. The lower green breccias 
are quite like those near the diorite body farther north. They are charac- 
terized by the presence of pumiceous fragments of a brighter green, and 
earry quartz, sanidin, and a little plagioclase. The large proportion of 
glass in these breccias offers a most inviting field for microscopical re- 
search. A full account of their interesting details may be found in 
Volume VI. The green rhyolitie breccia occurs again at the eastern 
end of the canon, but is here wonderfully rich in free quartz, which com- 
poses fully one third of the mass Along the west of the breccias is a later, 
solid porphyritic rhyolite containing quartz and sanidin, in a groundmass 
very rich in glass. The sanidins are noteworthy for their property of lab- 
radorizing. The sky-blue color, more brilliant even than the labradorizing 
orthoclases of Fredericksviirn, is entirely free from those minute bodies 
interposed between the laminz of feldspar, which in the case of the labra- 
dorite in the Norwegian occurrence have been supposed to account for the 
remarkable optical properties. In the Fortieth Parallel limit this labrador- 
izing sanidin is confined to an area comprising the rhyolites of the Pah- 
Ute, Desatoya, and Augusta mountains. Outside of that it has not been 


noticed, but within this comparatively narrow limit it occurs very fre- 


632 SYSTEMATIC GEOLOGY. 


quently, and might be considered one of the characteristics of the rhyolites 
of the region. This sanidin contains soda in almost equal percentage with 
potash. 

Of the Augusta and Fish Creek mountains, which form one distinct 
range of elevations, about a twentieth of the exposure is of ante-Tertiary 
rocks — granites, Triassic limestones, porphyries, and diabases; the granite 
probably Archzean, and all the rest not later than the close of the Jura. 
With this very slight exception, the entire range is covered with rhyolites 
which not only serve to mask the earlier underlying formations, but are 
themselves piled up to an extraordinary thickness. Viewing the range 
in profile from the western side, there are four prominent masses: that of 
the Fish Creek group, of which Mount Moses is the dominant peak; the 
Boundary Peak mass; the hills to the north of Shoshone Pass; and the 
high summit which lies between Shoshone Springs and Antimony Canon. 
At the last named locality, the edges of rhyolitic beds which are seen 
gently inclined to the northeast, show an exposure fully 6,000 feet thick, 
and the Boundary Peak and Mount Moses bodies are not likely to fall 
much below this amount. It is quite safe to say that the whole of this 
range is covered with a body of rhyolite from 2,000 to 7,000 feet thick. 
The exposure is nearly 100 miles long by from 12 to 20 miles wide. The 
inclination of the rhyolite tables, where any bedding is apparent, sometimes 
reaches as high as 15°; as, for instance, on the ridge between Antimony 
Canon and Shoshone Pass. When we reflect how great must have been 
the orographical disturbance connected with the Basaltic period altogether 
subsequent to that of the rhyolites, it would not be strange if the bedded 
rhyolites which represented the successive flows of that period were thrown 
into a dip considerably in excess of that of the natural angles of flow. It 
will not do, therefore, to assume that so high a dip as 15°, which is fre- 
quently to be seen in the Augusta Mountains, represents the natural angle 
at which the sheets of rhyolite flowed out. 

Over this great area is exposed an enormous variety of special rhyo- 
litic types. Where successive flows are exposed, it is often evident that 
the character of the rhyolite changed with each outpouring, making alter- 


nations of gray tuff material, black pearlites, a variety of vitreous breccias, 


RHYOLITES. 633 


and of solid, stony, crystalline rhyolite in which sanidin and quartz form 
a large portion of the total mass. These minute changes, without con- 
siderably varying the ultimate analysis of the rhyolite, produce an enor- 
mous number of varieties 

If there is any general law which comes out of this tangled mass of 
ejecta, it is, that the earliest eruptions were of a glassy and brecciated type, 
and that the later ones were more solid and porphyritic. As a ‘general 
rule, the higher and central portions of the range lack the bedding which 
may be seen toward the foot-hills on either side. In the Mount Moses 
region the enormous thickness of rhyolite is comparatively without bed- 
ding. The same is true of the great exposure at the head of Clan Alpine 
Canon, while on the other hand Boundary Peak shows on its western 
base the red edges of a vast series of beds. With such very limited ex- 
posures of the older rocks through which the rhyolites must have found 
their way to the surface, it is impossible to determine the characters of the 
vents. That they were not volcanic is very evident from the general forms. 
Like most of the other massive eruptions, they have doubtless come 
through long fissures riven in the underlying rocks down to the melted 
source. In other words, they have resulted from the outpouring of a chain 
of dikes, in this instance more than 100 miles in length. When we con- 
sider the long lines of fault which have been brought to light by the labors 
of Powell and Gilbert, together with those which this Exploration has 
examined—lines often 100 and sometimes 200 miles in length—it does not 
seem strange that systems of volcanic outflows should occur for correspond- 
ing distances. 

As between the more massive bodies of rhyolite and those which are 
distinctly bedded, there are apt to be characteristic lithological differences. 
The stratified rocks show either that water was a constant occurrence of the 
eruption, as in the case of the tuffs and some breccias, or else the presence 
of a considerable amount of glass, as in the pearlitic varieties and those 
having a large amount of glass base. The tuffs and some clearly stratified 
earthy varieties have uniformly a considerable decomposition of feldspars, 
resulting in kaolinie substances. 


Among many interesting types of rhyolites in these mountains, a few 


634 SYSTEMATIC GEOLOGY. 


may be profitably mentioned. The massive rhyolites around the head of 
Clan Alpine Canon are rich in macroscopic crystallized minerals, quartz, 
sanidin, biotite, and a little plagioclase. A variety from the mouth of Clan 
Alpine Cation, equally rich in dark granules of brown quartz and sanidin, 
contained also finely developed sphzerolites. The color at this locality is 
usually white, and biotite is almost invariably wanting. With these are 
also associated white breccias, made up of the same mineral combinations, 
portions of which are distinctly spherolitic. A later rhyolite, skirting the 
ghly crystalline porphyritic type, red, and rich 


oS 


eastern foot-hills, is of the hi 
in sanidin, biotite, and quartz, containing also more or less slender prisms of 
triclinic feldspar. North of Granite Point are white porphyritic rhyolites 
with a fine microfelsitic groundmass, containing abundant crystals of quartz, 
sanidin, and a little black biotite. Here again are associated white breccias, 
though less decomposed than the ordinary types. On the main mountain crest 
north of Antimony Canon are dark-gray, ashy-colored, and drab varieties, 
consisting of a banded gray felsitic groundmass, often inclining to yellowish 
and brownish tints, in which are quartz and sanidin. Passing downward 
in the series, this is underlaid by an unusually black pearlite, which con- 
tains in the prevailing dark glass a few cracked and shivered crystals of 
glassy sanidin and occasional quartz. 

Southwest of Shoshone Pass are some porous rhyolites of light-reddish 
colors, followed to the north by white rhyolites with an exceedingly fine, 
hornstone-like groundmass bearing a few sanidins and quartzes, with occa- 
sional triclinic feldspar. Immediately overlying this is a bright, emerald- 
green rhyolite of equally fine microfelsitic groundmass, but differing from 
the white variety by the presence of spherolites. In passing upward there 
is a vast series of varied beds, partly pearlitic, partly earthy, partly ecrys- 
talline, and porphyritic, following one another in rapid succession. 

In the region of Shoshone Springs are two distinct types, earthy pink 
and green varieties, and dark pearlitic sheets containing sanidin and quartz. 
The rhyolites of the Mount Moses region are of reddish-gray and yellowish- 
gray colors, and of a crystalline-granular groundmass so coarse as to pro- 
duce a rough, porous habit and lead to the ready disintegration of the rock. 
Large black quartz granules, shattered sanidins, and occasional triclinic 


RHYOLITES. 635 


feldspars are the only crystallized minerals, hornblende and mica rarely or 
never appearing. 

Near Dacy’s Canin is a little different type, with a very compact, dark 
groundmass, in which are black quartz and vitreous sanidin, besides dark 
magnesian mica. Beneath these is a series of finely bedded rhyolites, 
whose escarped edges show bands of red, yellow, chocolate, and gray, gen- 
erally of an ashy or earthy texture. Here is another instance of the earthy 
and more bedded rhyolites, which approach the habit and texture of a true 
tuff, occurring as the earlier ejection, followed by solid rocky varieties. 

The northern portion of the Fish Creek Mountains is a promontory of 
rhyolite, with a gently inclined surface and generally tabular structure. 
Skirting the western base are a few outliers of rhyolitie hills. They are 
distinct volcanic cones, and are completely surrounded by the Quaternary 
deposits of the plains. Those in front of the entrance of Dacy’s Canon 
are of rhyolitic pumice and ash, of light-gray and cream-gray colors. 
The mass is chiefly composed of rapilli and tuff, held together by a feld- 
spathic cement. These little hills are exceedingly interesting as being the 
only true voleanic cones within the field of our research. Their relation 
to the main rhyolitic mass of the Fish Creek Mountains is doubtless the 
same as that of the small, parasitic cones to so many of the great volcanic 
cones of the world. They are also of interest because through their 
vents, after the completion of the rhyolitic cones, limited ejections of in- 
tensely black basalt have taken place. The lower portions of the cones 
consist of light creamy-gray rhyolites, the summit being capped by black 
feldspar basalt. The latest eruption was a scoriaceous basaltic lava, 
which poured down the flanks of the rhyolitic cone and flowed out for a 
quarter of a mile upon the plain. Its surface is still uncovered by soil 
or vegetation There is no possibility of mistaking here the younger age 
of the basalt. The relations of this whole great field of rhyolite to the 
other volcanic rocks is completely in concord with the law of Richthofen. 
The rhyolites are later than the trachytes and andesites, and earlier than 
the basalts. , 

The mass of Battle Mountain consists of a block of quartzites 
and limestones, which, relatively to the surrounding country, has been 


636 SYSTEMATIC GEOLOGY. 


lifted very high. The Paleozoic rocks break off abruptly in every direc- 
tion, and with the Shoshone Peak mass probably represent a broad anti- 
clinal. They are profoundly faulted, and, like all of the very high masses 
of Palxozoic rock, are not extensively invaded or covered by volcanic 
rocks. Rhyolites have burst through the Carboniferous limestones on the 
western side of the range, and also through the heavy quartzites in Wil- 
low Cafion, and have overflowed the eastern base of the group near Battle 
Mountain Station. But as compared with the Palzeozoic exposure, the vol- 
canic rocks occupy a very small part of the mass. At Willow Creek the 
most interesting exposure is a flat plateau of dark rhyolites showing a pre- 
cipitous, escarped face toward Willow Canon. The rock has a compact, 
microfelsitic groundmass of reddish and pinkish colors, containing abundant 
quartz in large transparent and brownish granules, a few broken feldspars, 
but neither biotite nor hornblende. : 
With the exception of two or three very limited outcrops along the 
immediate foot-hills of Havallah Range, the rhyolitic rocks are confined to 
the north and south limits of the range. The elevated and continuous body 
of Triassic strata approaching Humboldt River is suddenly broken off, and 
does not reappear for a long distance northward. Where the block has 
gone down, as usual, a flood of rhyolite has come to the surface and makes 
the present northern foot-hills of the range. It forms considerable hills, 
from 1,000 to 1,500 feet high, of rough, irregular contours, margined on the 
north by heavy Quaternary accumulations, and touched at one point by the 
overlying horizontal Humboldt Pliocene. The average groundmass of this 
area varies in coarseness, but is chiefly a microfelsite, in which are a few 
scattered sanidins, biotites, and hornblendes, and shows a reddish-gray 
color from the abundance of decomposed ferrite. The extreme northern 
point of the outcrop varies considerably from this, in that the groundmass is 
pearl-gray, sanidins are very large, hornblende not infrequent, and the large 
granules of cracked quartz resemble the quartziferous trachytes of the 
range, and those of the Cedar Mountains of Utah and the Elk Head region 
in Colorado. At the southern end of the range, where again the Triassic 
ridge comes to an abrupt termination, the sunken or ingulfed portion of the 


range is replaced by a great outburst of rhyolite, rising 2,000 feet from the 


RHYOLITES. 637 


valley. The most interesting characteristic of this tongue of rhyolite which 
projects from the Havallah Mountains is its extreme height with so narrow 
a foundation. All along the eastern base basalts more recent than the 
rhyolites have burst through and overflowed its foot-hills. 

In Pah-Ute Range the rhyolites, as usual, bear an interesting relation 
to the fractures and dislocations of the older rocks. Granite Mountain, an 
island of Archzean rocks, flanked both on the north and south by great moun- 
tain masses of Triassic strata, descends abruptly to the south. The body 
of Triassic rocks, which extends in a southerly direction, dips to the east. 
The western face is a steep mountain front, made up of the edges of easterly 
dipping beds. The westward continuation of these beds is entirely lost, 
having been faulted vertically downward out of sight. Directly along the 
line where this fault must necessarily be, and according to the rule so often 
mentioned, the rhyolitic rocks have outflowed over the sunken block. 
Directly south of Granite Mountain is one of the most interesting of 
these masses, a ridge parallel to the main mass of the Triassic rocks, and 
rising above the plains in rounded heights of 1,100 or 1,200 feet. The 
eroundmass, of a buff and cream-gray tint, is of ferrite needles and 
spherolitie accumulations. This rock is interesting for the high propor- 
tion of fresh, brilliant, macroscopic minerals enclosed in the groundmass— 
remarkably regular dihexahedral quartzes rich in glass inclusions, some 
black hornblendes, and shining, jetty flakes of biotite. 

Upon the opposite side of the range, along the eastern foot-hills, a mass 
of diorite breaks through the Triassic strata, which, like the diorites of the 
adjoining ranges, came to the surface in the great post-Jurassic period of 
dislocation and fold. The same local weakness has given vent again to a 
powerful outburst of rhyolite, which lies directly to the east of the diorite, 
having overflowed it. At the northern limits of the rhyolite body, where it 
comes in contact with the limestone, it is seen to be more or less charged 
with bowlders of limestone and quartzite, showing that it has come up 
through the Mesozoic beds. Petrographically this mass of rhyolite differs 
entirely from those across the valley in Augusta Range, or the last described 
body on the westward base of Pah-Ute Range. Here the rock is minutely 
microfelsitic, frequently approaching to porcelain, and having singularly 


638 SYSTEMATIC GEOLOGY. 


few minerals recognizable by the unaided eye. The subjoined description 
from the writer’s notes in Volume II., page 697, conveys an idea of this 
interesting locality : 

“Tn the canon which trends north from the Sou Hot Springs is a 
remarkable dark Indian-red variety, consisting almost exclusively of a fine 
lithoidal base, in which are a few sharp, brilliantly defined, and entirely 
fresh crystals of sanidin and minute particles of quartz. Through this 
base are waving, ribbon-like bands and strings of minute fibrous material, 
also more or less distinct aggregations of spheerolites, and narrow lines of 
devitrified glass. The latest of the flows, capping the others, contain well 
developed sanidins, a few small biotites, and concentric-radial spherolites. 
The flows of middle age appear to be chiefly lithoidal, while the earliest of 
all are formed of brecciated material. Here, as in many other localities 
among the rhyolites, the included fragments are composed of the same 
material as the binding paste; the latter, however, is more finely felsitic, 
the crystallized minerals being very minute; whereas, in the included frag- 
ments, there are large dihexahedral quartz crystals, and sanidins one eighth 
of an inch in length. A peculiar feature of this breccia is, that the forms 
of the included fragments are rounded, and show, in the outer eighth of an 
inch of their section, decided caustic phenomena. In some instances, 
where the included fragments have been considerably fissured, and earthy 
decomposition has taken place, the sphzerolites are destroyed, leaving 
spherical cavities; the whole mass being tinged reddish-yellow by the infil- 
tration of iron oxyds, which are probably developed from the ferritic 
needles of the groundmass. Here, also, it is noticeable, as in many other 
localities, that the breccia-flows form the earliest of the rhyolitic series. 
These lithoidal varieties of rhyolite differ so characteristically in their 
physical aspect from those found on the opposite side of McKinney’s Pass 
(an analysis of which is given in the table following this section), that an 
analysis of the Indian-red rock just described was made by Mr. R. W. Wood- 
ward, to determine, if possible, any marked distinctions of chemical or min- 
eralogical composition. The two analyses, as will be seen in Table XL, 
agree very closely, showing less variation than may be found in any two 
highly crystalline rocks of the same species.” A considerable portion of 


RHYOLITES. 639 


this rhyolitic exposure has a rather thin covering of more recent steel-gray 
basalt. 

From the region of Cottonwood Creek nearly down to Sommers’ Pass 
there is a complete gap in the sedimentary series, the middle of which is 
occupied by huge massive diorites, that make up the centre and summits of 
the range. Both north and south extensive fields of rhyolite have broken 
out, and those along the northern summit and western base are covered by 
a broad field of basalt, which inclines toward the northern valley, the sedi- 
mentary rocks having been depressed and their places taken by the volcanic 
series. The rhyolites are later than the small body of trachyte along the 
eastern side of the diorite, and earlier than the heavy masses of basalt which 
at Table Mountain overlie the acidic series in deep and extensive sheets. 
The rhyolites north and east of the diorite mass along the heights, and 
down to within 300 or 400 feet of the plains, were a subaerial ejection, and 
are chiefly of a reddish-gray groundmass, in which quartz, sanidin, and 
biotite are thickly studded. Among the sanidins here recurs the blue, 
labradorizing variety, with a more intense play of color than is elsewhere 
seen. Hand specimens sparkle with a peculiar brilliant opalescent light, 
flashing out the most exquisitely pure and delicate blue. Microscopic exam- 
ination shows them to be identical with those already described from the 
Desatoya Mountains, and to lack the minute foreign particles which are 
characteristic of labrador and the labradorizing orthoclases of Fredericks- 
virn. The reader is referred to Volume VL, page 183, for Professor 
Zirkel’s interesting notes on this occurrence. Enough of the blue sanidin 
was collected for an analysis (see Vol. IL, p.702.), from which it is evident 
that it is a true sanidin, in which the soda equivalent nearly equals that 
of potash. 

Down the eastern slope from the iridescent rhyolites are earthy- 
brown varieties crowded with biotite, and these, in turn, are succeeded by 
a vast series of sub-lacustrine rhyolitic tuffs, which are distinctly bedded 
and in nearly horizontal position. These soft, earthy strata of cream-col- 
ored, gray, and pale-reddish hues are weathered in soft round forms almost 
approaching some of the Bad-land sculpture. Their peculiar aspect is 
shown in Plate XX. Some of the strata contain an unusual proportion of 


640 SYSTEMATIC GEOLOGY, 


glass, and others are reduced almost to clay by the kaolinization of the 
feldspars. 

South of Chataya Peak the summit of the range is made up of soft, 
easily decomposable rhyolitic beds of purple and gray, showing, within 
what is evidently a part of the same flow, great variation in texture and 
even in composition. Biotite and quartz are usually present in about the 
same proportions, but through the rhyolitic mass are clouded, irregular re- 
gions almost destitute of these two minerals, where the light grayish and 
buff rhyolites are mostly rather coarsely felsitic. The coarser varieties 
closely resemble trachyte in their field habit, but the presence of quartz 
in the groundmass and the distinctly fluidal structure revealed by the 
microscope classes them positively as rhyolites. 

Of West Humboldt Range only the southwestern half displays any 
rhyolitic eruptions. Standing anywhere in the neighborhood of the north- 
ern end of Humboldt Lake, and looking toward West Humboldt Range, 
one sees the dark elevated body of Triassic strata which extends southward 
from Oreana suddenly break down in a line south of Lovelock’s Station. 
The brilliant red, pink, gray, and white confused hills, which continue 
the line of mountain elevation, are of rhyolites, and take the place of the 
section of sedimentary rocks which has gone down. 

South of Humboldt Lake itself rises a lofty ridge of highly inclined 
Triassic beds, which represent the continuation of the sedimentary series. 
Its northern edge plunges down quite abruptly to the low level of.the rhyo- 
lite hills. In other words, the rhyolite occupies a depressed region which 
might be termed a broad, extensive pass between the two blocks of elevated 
strata. Still to the southwest these inclined stratified rocks suddenly break 
down again in a depression, which is occupied by the rhyolitie eruptions of 
the Mopung Hills. 

South of the town of Oreana, at the western base of the range, in con- 
tact with the Jurassic slates, is a narrow line of rhyolitie eruptions which 
are of no special importance. The real interest of the volcanic rocks of this 
range centres about the Mopung Hills. The rhyolites wrap around the 
southwestern termination of the Tebog Peak Triassic body, rising high on 
the flanks of the limestones that form the most southern point of the strati- 


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RHYOLITES. 641 


fied mass. From the desert plains upon either side the rhyolites rise to a 
height of 1,000 feet, and are made up of a wonderful variety of colors and 
forms. Taken as a whole, they are finely microfelsitic; the ground- 
mass, made up of quartz and sanidin, containing singularly few secretions 
of macroscopic crystals. Small but brilliant sanidins, and quartz both black 
and colorless, are the only visible minerals. The earliest eruptions were of 
gray and pink breccias, altogether made up of the fine felsitic materials. 
These breccias formed a considerable portion of the whole eruption, and 
are noticeable for the sharp, angular character of the fragments which 
they enclose. The proportion of angular fragments to the magma is ex- 
ceedingly large. The ejection was really a rush of finely crushed rock, 
merely given a sufficient fluidity to insure motion by a scanty magma of 
finely felsitie material. White and flesh-colored felsitic and porcelaneous 
rhyolites broke through the breccias, and these again were invaded and 
capped by gray pearlitic types. 

Among these hills were collected some of the most singularly beauti- 
ful lithological products that can be imagined—ribanded varieties made 
up of chocolate-colored, pink, salmon, white, and pale-green. Upon the 
southern slope of the hills are porous, earthy types in which a kaolinic 
decomposition of the sanidin has occurred. 

The northernmost limit of this flow, directly south of the outlet of 
Humboldt Lake, shows some interesting rhyolites containing abundant 
crystals of sanidin and triclinic feldspars. A dark, chocolate-colored variety 
rich in biotite, and a further reddish-brown variety, with dark, chocolate- 
colored spherolites, are among the interesting types. Striped and banded 
varieties, resembling the ribanded jaspers, are very common here, with a 
cream-colored and gray groundmass, lined with red and purple. These 
northern foot-hills are deeply fissured, and at certain places there has been 
a great deal of local decomposition, the cavities of the rock being filled with 
carbonate of lime, and many of the fissures being incrusted to the thickness 
of a quarter of an inch with common salt. Analyses of two types are given 
in the table of analyses at the close of this section. These analyses are 
of interest as showing that two specimens of the same outburst, of widely 
diverse appearance, are really chemically identical, and that the divergence 

41 Kk 


642 SYSTEMATIC GEOLOGY, 


of texture and color may be ranked as accidental results, depending upon 
phenomena of devitrification and decomposition. The only other eruptive 
rock associated with the Mopung rhyolites is a small body of basalt near 
Mirage Lake, which overflows the western terminus of the rhyolites. 

Next to the great rhyolitic area made up of Augusta and Shoshone 
ranges and their northeastern continuation, the most interesting and at the 
same time the most extensive region in Nevada is that of Montezuma Range 
and the adjacent Kamma Mountains. The northern and middle parts of the 
range are made up of granite and the associated Archean schists overlaid 
by the unconformable Jurassic slates. Important masses of basalt and 
rhyolite make up the rest of the ridge. No range shows a more diversified 
profile, and in none is the geological relation of the volcanic to the older 
rocks more difficult to ascertain clearly. The rule which I have traced 
with such apparent uniformity so far, that the rhyolites have come up in a 
region of depression, seems to hold here. 

Where the granite and Archzean schists of the region of the Monte- 
zuma Mine, passing northward, are abruptly terminated, there are upon the 
eastern side of the range bodies of rhyolitic hills, and upon the western, 
basalts. So to the south of the central mass which culminates in Trinity 
Peak, the Archean schists and granites fall off and are immediately overlaid 
by extensive accumulations of the eruptions of rhyolite and basalt. 

The rhyolites northwest of Black Cafion make a group of hills 
through which rise occasional islands of granite, and which are margined 
along the north and east by slightly disturbed ashy strata of the Truckee 
Miocene. The low character of the hills, and the granite islands that 
penetrate them, give the impression of a rather shallow covering of rhyolite, 
and the structure of the rock itself is that of a thin flow. The rock is gray, 
of a rather uniform microfelsitic groundmass with few visible sanidins, but 
clouded and penetrated by very peculiar, irregular masses of pearlite, 
hornstone, and obsidian, the latter varying in color from nearly black to 
almost pearly gray. 

An interesting occurrence is that along the southern margin of the 
rhyolite body. Here is a buff, purple, and isabel-colored body having a 
fine lithoidal base, with a few small, brilliant, uncrystallized granules of 


RUYOULITES. 643 


quartz and a little sharply defined sanidin. The aspect of the rock is 
decidedly porcelaneous, resembling a great many forms of petrified wood. 
In the prevailing gray and yellow color are stripes and wavy cloudings of 
purple, lavender, and pale-gray, sometimes with passages of a bright 
sulphur-yellow. It breaks with a distinctly porcelaneous fracture ; and the 
analysis, given in Table XI., shows a composition strikingly similar to that 
of the opposite type of rhyolites from Pah-Ute Range. The latter, rich in 
crystals, has a rather coarsely microfelsitic groundmass made up of sanidin 
and quartz, while in this the abundant silica, reaching 75 per cent., has gone 
into solution in the porcelaneous groundmass. The microscope reveals a 
few quartzes and feldspars, but no biotites, and the groundmass develops 
a structure decidedly worth noting. (See Volume VI., Plate VIL, Figure 3.) 

A rhyolite deserving mention occurs at Lovelock’s Knob, an isolated 
hill a few miles south of the mouth of Valley Canon. Here is a granitic 
boss rising like an island out of the horizontal Pliocenes, which in this 
neighborhood are thinly covered with Quaternary. The granite is broken 
through and overflowed by a mass of rhyolite showing a wonderful variety 
of texture and color. The prevailing type is a creamy or gray earthy 
breccia, which passes into dark umber colors and again into red and pink 
tints. The mass forms a capping upon the surface of the granite 500 or 
600 feet thick, the only other associated rock being a small development 
of basalt on the north side of the knob. 

The southern half of Montezuma Range is mostly made up of rhyo- 
lites, here and there masked for no great thickness by black and steel- 
gray basalts. In the region of Valley Canon are exceedingly interesting 
pearlitic rhyolites, which have broken through the more crystalline varieties 
that lie west of them. These glassy and half glassy rocks are rich in 
large, cracked sanidins half an inch long, considerable shining hexagonal 
plates of biotite, and a little rather earthy hornblende, all embedded in a 
gray, yellow, and brownish-yellow base. Their mode of occurrence lends 
them their main interest. The pearlite ridges which stand out distinctly 
from the surrounding surface of easily eroded rhyolites show a development 
of fine, hexagonal columns, whose axis is inclined at an angle of about 80° 


from the horizontal. 


644 SYSTEMATIC GEOLOGY. 


The great body of rhyolites forming the southern end of the range is 
made up of a wonderful variety of superficial appearances—differences of 
habit and texture, differences of color, and behavior of groundmass; but all, 
with few exceptions, belong to two general types, namely, the glassy and 
half glassy varieties, and the lithoidal microfelsitic. 

In Bayless Cation occurs what is perhaps the most remarkable rhyolitic 
display of the whole region. It consists of a ridge more than a mile long 
and rising 300 or 400 feet above its surroundings, altogether made up of 
well developed prismatic columns, varying in size from two feet in diameter 
down to an inch. The cross-section along the ridge would show a sharp, 
roof-like form coming to an exceedingly thin blade, which bristles with fine 
vertical columns. Upon either side, in descending toward the foot of the 
slope, the columns are seen to incline from the centre outwardly, while 
at the middle of the ridge they are tossed into a variety of angles, but 
approach the vertical. The steep slopes are formed of sharply divided col- 
umns, still in situ, resembling a pile of architectural ruins and suggesting 
the name of Karnak. Plate X.XI. is a view of the crest of the Karnak rocks. 
The exterior of the columns, generally of a dark, almost chocolate-brown 
color, fades in many instances into a reddish-gray. The interior is an 
exceedingly brilliant, pure gray, formed of a rather coarsely crystalline 
groundmass in which are embedded brilliant sanidins, well preserved biotites 
and hornblendes, occasional but rare limpid granules of quartz, and a few 
triclinic feldspars, the microscope adding to these an abundance of apatite. 

The western fork of the same cafion enters a region which is one of the 
most brilliantly-colored bits of geology in the whole West. The rhyolitic 
hills show a general tendency to horizontal bedding, and are made up 
of lithoidal varieties, some of which have passed into an almost earthy 
condition, and which vary from snowy white, like those of the Mopung Hills, 
through brilliant vermilion-red to orange, gray, purple, yellow, and green. 
A more bizarre and extraordinary assemblage of colors is rarely to be met 
with in nature. 

At the southern base of the range, near White Plains, is also an inter- 
esting locality. Here the inclined Miocene strata, made up of trachytic 
tuffs and ashes, and beds of infusorial silica, are broken through by two 


RHYOLITES. 645 


successive outpourings of rhyolite. The first is of a rather warm gray, 
and is distinctly bedded, the layers inclining toward the east about 80°. 
Across these most prominent structure-planes are jointings that divide 
the rock into rude approaches to columnar forms. Examined in detail, 
these rhyolites are seen to be laminated almost as finely as the leaves 
of a book. The gray material is striped with fine, delicate lilac and 
brown bands. Through this laminated series has burst a gray and olive 
glassy rhyolite, rich in flakes of biotite—a rock which has the singular 
property of forming a brilliant varnish-like glaze upon the surface of all 
exposed blocks. This glassy rhyolite contains large crystals of sanidin 
and a few granules of quartz, and is not far removed petrologically from 
the columnar pearlites at Valley Canon. 

The little group of the Pah-tson Mountains is distinguished by an in- 
teresting assemblage of rhyolitic types. The long ridge projecting south- 
ward from Aloha Peak is formed of dark-brown tabular masses of rhyolite 
escarped toward the north and east, developing a rude bedding which is 
not unlikely to be the original planes of flows, having a dip reaching 
30° to the east. It is suggested that this high angle may be the result of a 
dislocation at the time of the subsequent basaltic eruptions. The main 
material is of trachytic habit and reddish-gray color, the felsitic groundmass 
showing alternating stripes of red and gray pores and carrying a little mica 
and glassy sanidin as macroscopical secretions, the microscope revealing 
also plagioclase, quartz, and certain undetermined microlites. 

Surrounding the basaltic ridge west of Aloha Peak are gray rhyolites of 
pearlitic type crowded with black biotites and carrying a few sanidins and 
brown hornblendes. The eastern foot-hills of the range, at the base of Pah- 
keah Peak, show two varieties of rhyolites, one a compact, fine-grained rock, 
largely made up of minute glassy sanidins and quartz, the other a mauve 
breccia, containing opaque kaolinized feldspars. 

Directly north of Pah-keah Peak, on the heights of the range, is a com- 
pact, greenish-yellow, quartz-bearing rhyolite having a dense microfelsitic 
groundmass, the average specimens resembling older porphyries. With this 
was observed a white rhyolitie breccia containing fragments of a lithoidal 


green variety. The felsitic groundmass and the binding magma being harder 


646 SYSTEMATIC GEOLOGY. 


than the included fragments, the fracture-planes pass through both alike. 
Farther north, near the head of Grass Canon, are more white rhyolitic 
breccias of scoriaceous habit, the interior of the cavities being colored red, 
the groundmass bearing sanidin and quartz. The pearlitic varieties dis- 
played along the head of Grass Cation merit so particular a description 
that the following paragraphs are quoted from Volume IL.: 

“Grass Canion, which is a long, narrow ravine running out at the north- 
ern end of the mountains, presents along its slopes the most interesting 
occurrences of volcanic rocks in these mountains. At its head, and along 
the upper walls, are gray pearlites of the crystalline type. A characteristic 
specimen is rich in black biotite, and contains macroscopical crystals of san- 
idin, plagioclase, and quartz. Under the microscope, the feldspar crystals 
are seen to contain great numbers of angular bubble-bearing glass-inclu- 
sions, sometimes so closely aggregated as to form entire portions of the 
interior of the crystals. Mica is most abundant in hexagonal lamine, 
0.008"™" in diameter, while in the colorless glass base are feldspar-microlites 
and pale-green needles, together with gas-cavities containing magnetite. 
This pearlite passes into one in which the crystalline ingredients are still 
present, but the groundmass is a colorless glass, in which are developed 
concentrically curved cracks, giving a spherolitic structure to the mass. 
Microlites are present as products of devitrification, and, as already stated, 
crystalline ingredients, feldspar and mica, which are difficult to detect with 
the unaided eye. Beyond the pearlites, on the west side of the canon, 
about opposite North or Basalt Peak (not named on the map), is a peculiar 
greenish rock, having in general a granular structure, and showing no crys- 
talline ingredients, through which run many bands, alternately quite porous 
and again compact and lithoidal. The latter pass into chalcedony, which 
covers the weathered surface, and sometimes forms the mass of the rock in 
bands a foot or more in thickness. 

“At the head of a side-ravine, where, in a low saddle, the underlying 
rocks have been denuded, is disclosed a most interesting series of rhyolitic 
pearlites, chalcedonies, and tuffs, which, from the occurrence of rounded 
obsidian balls within the pearlite layers, have been designated the Ball 


Rocks The upper layers on either side of this saddle are composed of 


2H YOLITES. 647 


the green rhyolite already mentioned, and layers of brown chalcedony, on 
whose weathered surfaces are curious rounded excrescences, of concentric 
structure, resembling the gnarled growths found on old tree-trunks. This 
similarity is heightened by the color and interior banded structure of the 
chalcedony, which resembles woody fibre. Within the chalcedony mass 
are frequent druses, lined with white banded opaline agate, and containing 
quartz crystals. Zirkel describes the microscopic structure of the chalced- 
ony as consisting of concentric globules and botryoidal concretions in a 
seemingly colorless substance, which by polarized light is seen to be an 
ageregation of siliceous spheerolites. A section is represented in Volume 
VL, Plate XIL, Figure 2. 

“On the saddle are exposed layers of pearlite, containing rounded ob- 
sidian balls, from half an inch to an inch in diameter, associated with a 
white pumiceous tuff, enclosing fragments, generally rounded, of the pearl- 
ite. The pearlite is blue-gray, devoid of crystalline ingredients, with a 
tendency to form layers from an inch upward in thickness. It has a 
wavy appearance, and is entirely made up of spherolitic concretions. The 
spherolites have a concentric structure, and are formed of thin layers. 
Under the microscope, these layers are seen not to be complete rings, but 
to be grouped round the centre like the leaves of an onion, and the micro- 
litic products of devitrification to be arranged in parallel wavy bands 
through the mass, quite independent of the concentric structure, from which 
Professor Zirkel concludes that this structure is merely a phenomenon of 
contraction. The pumiceous tuff, which is found abundantly along the 
slopes of the ridge, is a white porous mass, containing small fragmentary 
crystals of quartz and sanidin, and enclosing larger fragments of the gray 
pearlite, in contact with which the white frothy matrix is seen to be com- 
pressed and hardened, so that the surface of the cavities left by these frag- 
ments is smooth and hard like a plaster mould. 

“The obsidian balls, which have an almost perfectly spherical shape 
and occur imbedded in a layer of pearlite, near the summit of the saddle, 
are seen by microscopical examination to be remarkably pure, containing 
only a few trichites in a light-gray glass. 


“ About a mile from the mouth of Grass Canon occurs another white 


648 SYSTEMATIC GEOLOGY. 


rhyolitic tuff or breccia, of much more compact mass than the above, and 
enclosing fragments of dark porphyritic rhyolite with free quartz, which 
forms quite high cliffs on the west wall of the cation. 

‘Tn this vicinity, also, is a considerable development of basaltic rocks, 
which have apparently poured out on the east side of the cation, and have 
covered the upper part of the ridge on the west. These basalts develop a 
columnar structure, particularly on the slopes of the peak on the east side, 
which has been called Basalt Peak, where they are remarkably perfect and 
arranged horizontally. They belong to the same general type as those of 
Aloha Peak. The main mass is a compact, dark, rather vitreous-looking 
rock, with conchoidal fracture and somewhat coarse texture, in which only 
small plagioclase crystals can be detected macroscopically. The micro- 
scope detects also olivine and augite, and in the groundmass an amorphous 
globulitic base.” 

The Kamma Mountains, which are really a northern continuation of 
the Pah-tson, are divided into two distinct groups. The southern one is 
composed chiefly of andesites that have broken through Jurassic slates, 
while the northern body, made up of lofty, rugged hills, is almost entirely 
of rhyolite and rhyolitic breccias, and, around the lower portions, of a group 
of tuffs. The predominating breccias display in the angular fragments 
which they conain a very great variety of microstructure of groundmass. 
Earthy, rearranged, rhyolitic tuffs occupy the lower foot-hills. Northward 
from this group the desert slopes are dotted with little rhyolitic and ande- 
sitic hills, the former not greatly differing from the Kamma rhyolites. 
Farther north the western foot-hills of the group which forms the eastern 
boundary of Quinn’s Valley are of porous, earthy-white rhyolites, contain- 
ing only sanidin and quartz. These rhyolites are of interest, as they are 
seen to have disturbed and tilted the Miocene strata. 

West of the valley of Quinn’s River, in the very heart of Mud Lake 
Desert, is the group of Black Rock Mountains, rising at extreme points 
about 1,000 feet above the desert level. Within the area of our map it is 
built of rhyolitic and basaltic eruptions; and the minor ridges which 
make up the topography are usually capped with a sheet of basalt that 
inclines to the east, the rhyolites showing along the western base of the hills. 


RHYOLITES. 649 


This is repeated several times, giving the impression that the region has 
been disturbed since the eruption of the basalts. In one instance rhyolites 
appear to overlie the basalt directly ; and since this is the sole exception to 
the law of Richthofen within our limits, it was examined with some care. 
It was not clear whether the rhyolite had really come to the surface later 
than the basalt, or whether the basalt had broken through between beds of 
rhyolite, as it is often seen to have done between the strata of a sediment- 
ary series. The basalt is a true olivine dolerite, not at all to be mistaken 
for an augite-andesite. The problem, therefore, is purely one of structure, 
and requires further study to clear up all obscurities. Standing as a soli- 
tary exception in the face of such a multitude of concurrent examples to 
the contrary, this apparent succession of rhyolite after basalt must be 
attributed either to an obscurity of structure or to one of those curious 
alternating eruptions which are described by F. von Hochstetter.* 

A supposed exception was brought to light by the late Archibald R. 
Marvine at Truxton Springs, Arizona, where a light purple and gray rhyo- 
lite, rich in crystalline minerals, and having a rather coarsely crystalline 
groundmass, was observed to overlie a doleritoid rock. The writer ex- 
amined thin sections of the latter, and found it to contain minute grains of 
quartz, with specks which had the appearance of very minute fluid inclu- 
sions. The olivine had in large part passed over into a serpentinous con- 
dition, and the glass base was globulitically devitrified, as is so common in 
the middle-age diabases. The rock was therefore pronounced, without 
much hesitation, a diabase, and the law of Richthofen sustained. 

Westward from the Black Rock Hills, across an arm of Mud Lake 
Desert, rise the Forman Mountains, a group of irregular rhyolitic hills 
reaching about 1,200 feet above the level of the desert. Wherever 
examined, they prove to be altogether of rhyolite, for the most part a pure 
felsitic mass, of flinty, conchoidal fracture, containing as macroscopic secre- 
tions only a few half kaolinized feldspars. Farther up the range are some 
reddish, highly crystalline rhyolites, with rough, trachytic fracture, made 
up of sanidin and free quartz in a compact felsitic groundmass. With this 
is a breccia similar to the solid rock; and from a little north of our map 


* Reise der Oesterreichischen Fregatte Novara um die Erde, in den Jaren 1857, 1858, 1859. 


650 SYSTEMATIC GEOLOGY. 


was brought in a very wonderful example of minute rhyolitic columns 
closely welded together, each prism about one eighth of an inch in diame- 
ter. They are quite accurate hexagons, and are composed of a dark, steel- 
gray rhyolite, the fine, microcrystalline groundmass containing limpid 
quartz and small, slender crystals of sanidin. 

The rhyolites of Truckee Range are confined to the southern portion, 
directly abreast of the south end of Winnemucca Lake, and a single rhyo- 
litic summit which rises above the broad, basaltic masses directly north of 
Desert Station, in the most southern ridge. Here a single peak of gray 
and grayish-brown, half-glassy rhyolite is exposed, rising like an island 
above the basalts. It is very rich in brilliant biotite, and contains a little 
greenish-black hornblende, but no quartz; and the abundant glassy base 
shows the most interesting products of devitrification, as described by Pro- 
fessor Zirkel. Among the rhyolites east of the southern end of Winne- 
mucca Lake are none of special petrographical interest. They directly 
join the granites, diabases, and metamorphic Triassic strata, and are made 
up of rugged piles of brilliant pink, red, white, ashy, and lavender-colored 
rocks, which are quite conspicuous in their contrast with the darker masses 
of the metamorphic series. 

Since all of Virginia Range within the limits of our map is made up of 
eruptive rocks, and, with few exceptions, of Tertiary volcanic rocks, we 
have no clew to the relations of the rhyolites to the ancient series. They 
are quite subordinate, both in amount of exposure and in the position which 
they hold in the broad topographical features of the range. They are actu- 
ally confined to the skirts of the group and the low region of Mullen’s Gap. 
Between Black Mountain and the granite ridge which projects southward of 
State Line Peak, overlying the granites and in turn capped by more recent 
basalts at the extreme head of Louis’ Valley, is a small development of 
reddish-gray rhyolites with a finely felsitic groundmass and the most char- 
acteristic banded structure. Biotite, sanidin, and occasional quartz are the 
only visible secretions. 

At Mullen’s Gap, both north and south of the pass, are limited expo- 
sures of rhyolites which have broken through and overlaid the foot-hills of 


quartz-propylite, and northward they are themselves overlaid by broad 


RHYOLITES. 651 


basaltic sheets which come down from Black Mountain. How far the 
rhyolites may continue under the heavy, overlying masses of basalt is, of 
course, an open question. In these few foot-hills are to be seen a very 
great variety of rhyolitic types; some with felsitic groundmass crowded with 
secreted minerals—sanidins, plagioclases, quartzes, and biotites. With these 
are associated light, cream-colored tuffs, dark pearlites, and a wide range 
of glassy and half glassy varieties. The prevailing color of all the Mullen’s 
Gap rhyolite is a very brilliant Indian-red, not unlike those from Sou 
Springs. The most porous pearlites and the pumices, which here occur in 
great profusion, are of pearl-gray and lavender colors. Here, too, are 
found stratified pumiceous tuffs in which the material has been evidently 
rearranged in lacustrine waters. They are remarkably friable, crumbling 
at the touch like beds of volcanic ashes. An ash-gray breccia from the 
north side of the gap is made up of a loose, rather incoherent binding 
material and fragments of several varieties of more or less decomposed 
rhyolites. Sanidins are the only secreted crystals. That which lends the 
rock its interest is the occurrence of liquid inclusions in glass, and of an 
apatite included in glass, itself carrying a minute fluid inclusion. 

The most extensive rhyolite body in this part of Virginia Range occurs 
directly north of Truckee Canon, having its culminating-point at Spanish 
Peak. Here is a lofty, rugged hill, from which a rude bedding declines in 
every direction. These rocks have overflowed the sanidin-trachyte that 
forms the main summit of the range to the west, and in turn are nearly sur- 
rounded by basaltic outbursts, as seen upon the geological map. It is a 
pinkish-gray and lilae rock, of a fine-grained felsitic groundmass, contain- 
ing only a few macroscopic individuals of sanidin. Under the microscope 
it is seen to be very rich in tridymite and well rounded spheerolites. The 
most interesting petrographical feature is the extremely fine lamination 
visible at various points of its body. Hand specimens show laminations of 
not over a fortieth of an inch in thickness, and these are not merely parallel, 
straight lines, but are often contorted into regularly defined scollops, sharp 
points, and complicated, compressed waves. For the most part, these lami- 
nations are present in perfectly parallel, smooth planes, upon which the 


rock has a slight tendency to break. Approaching the river, the gray 


652 SYSTEMATIC GEOLOGY. 


and pink rhyolites overlie a dense white felsitic variety which is very rich 
in large, brilliant granules of quartz—a rock closely resembling the white 
felsite porphyries of middle age. Over this extremely white, pure variety 
of rhyolite, are the ends of a flow of excessively black, fine-grained basalt, 
affording the most extreme contrast in color and texture. 

In the region of Berkshire Cation, the eastern foot-hills of Virginia 
Range are composed of an important belt of rhyolites which have burst 
through and overflowed the trachytes and dacites. Seen from the valley 
of the Truckee, these rhyolitic foot-hills rise from 1,200 to 1,800 feet above 
the level of the Pliocene mesa, and in their rough exterior and suddenly 
variegated colors make a thoroughly characteristic rhyolite display. They 
are white, pale pea-green, salmon-colored, pale lilac, Indian-red, olive-brown, 
and deep purple. Directly north of Berkshire Canon they are broken through 
and overlaid by a small mass of basalt. Taken as a whole, this field of 
rhyolites, about twelve miles in length, shows almost no bedding whatever. 
It is a fine type of structureless, massive eruption. It embraces several 
petrographical varieties, shading through a dense white felsitic rock with- 
out a single macroscopic crystalline secretion, and through mica-bearing, 
quartz-bearing, and sanidin varieties, up to a highly crystalline rock with 
a scanty felsitic groundmass and a crowd of brilliant crystals of quartz, 
plagioclase, sanidin, and biotite. The quartz is invariably in rounded, 
cracked granules, the sanidins often dislocated and varying in dimensions 
from a fine point up to the size of a pea. One salmon-colored variety was 
characterized by an enormous amount of large, open cavities lined with a 
thick coating of siliceous sinter. The more solid parts of this rock were 
salmon-colored felsitic masses, so fine as to resemble the most close-grained 
jasper. Decomposed spheerolites are seen by the microscope to be very 
common. <A few of the more brilliant sanidins possess the labradorizing 
quality to a slight extent. 


Number of 
analysis 


LST) 


158 


LSS) 


160 


161 


162 


163 


166 


Wests 
Raj 
Huml 
Ray 


Pine } 


Tish ¢€ 


“ee 


TABLE OF CHEMICAL ANALYSES. XI—UNITED STATES GEOLOGI CAL EXPLORATION ¢ 


Rhyolites, 


Locality. Analyst. Si | At | te | Fe | Mn 


157 _Lassen’s Peak, California R. W. Woodward | 68.84] 15-73] - -| 3-11 


36.71 7-33 ae 0.69 


= Cialis x 68.98] 15-57] - -| 3:22 
36.78 7-25 are O.71 
13S Lassen’s Peak, Califomia - - - <e 69.66) 15-71] 1.02] 1-48 


37-15 7-32 0.30 0.33 
“ 


« 69.36} 16.23] 0.88) 1-55 
36.99 - F 


Kc 70.29| 14.85] 1-20] 1-20] 0.16 
37-48 6.81 0.36 0.26 0.03 


ey « « & 70.15] 14-51| 0-24] 1-20] o11 
37-40 6.76 0.37 0.26 0.02 

160 Westside McKinney’s Pass, Pah-Ute re 74.00] 11.93| 2.08] 0.67) . . 
Range. 39-46 5-56 0.62 0.13 ae 


161 Humboldt Sink Group, Montezuma cs 74-62| 11.96] 1-20} 0.10 
Range 39-79 | 5-57 | 0:36] 0.02 
“ « “ 


« 75-34) 11-68] 1-35] o.10] . .| O49] = - 


40.18 b 0.02 we: 0.14 


i162 Back of Montezuma Mines, Monte- 


c 74-95| 13:61] - -| 054] . -| 2.02] = = 
zuma Mountains. 3-97 . oa ae h Sea 


“ “ “ 


we y Ley fd (em oes leer acu fe 
39-93 ee aye . 8 


so 75:97 
49.04 


4 “ “ 75-1 5 
40.08 
164 Fish Creek Mountaims - - - - toad 
23 
“ ae - - - - 


75:55 | 
40-29 


165 Hot Spring Hills, Pah-Ute Range 15°65 


“ “ ¥ “ 715°7 
165 Mopung Hills, West Humboldt 
| Kange. 
“ “ “ 


SiC LONG eV: 
BASALTS. 


Like the rhyolites, the basalts show their most prominent development 
in middle and western Nevada. There are a few limited bodies around the 
northern edge of Salt Lake; and north of the limits of Map IIL, in the 
valley of Bear River, there are important but restricted basaltic areas. The 
great and repeated dislocations and orographical disturbances which have 
marked the region of the Wahsatch have been accompanied only in modern 
times by trachytic eruptions. No basalts are seen along the grander part 
of that range. North of the Fortieth Parallel limits, however, are basaltic 
areas which seem rather to be the outliers of the wide basalt country that 
borders the Snake Plains. 

On the eastern base of the Rocky Mountains, south of our work, are 
basaltic localities; but within the Fortieth Parallel limits the most easterly 
bodies are those exposed along the divide between North and Middle parks. 
As has been seen, the middle of that ridge is formed of a trachytic eruption, 
the eastern wall of North Park being lined with rhyolites. The basalts, 
which cover less area than either of these two, occur west of the trachytic 
masses along the eastern base of the Archzean slopes of Park Range. From 
a little north of the parallel of 40° 30’ they extend south beyond the limits 
of our map, a most important point being Rabbit Ears Peak. They extend 
eastward across the valley of the West Fork of the Platte, having an irregu- 
lar, rugged surface which rises here and there in rude domes. Near the 
Indian trail which crosses the divide from the head of West Fork, they dis- 
tinctly overlie the rhyolites, and west and south of Ada Springs appear as 
powerful dikes cutting through the Cretaceous sandstones which have been 
weathered away from their sides, leaving the basaltic walls projecting 
strongly above the surface. These dikes were observed to have a trend 
about northwest. Over the lower levels of the basaltic area, which is only 


about 15 miles from east to west, the horizontal strata of the North Park 
653 


654 SYSTEMATIC GEOLOGY. 


Pliocene have been deposited, abutting nonconformably against the basaltic 
slopes. ‘These lacustrine sandstones occupy a deep bay south of the Rab- 
bit Kars and west of the Ada Springs Cretaceous body, and cover all the 
basalts, with the exception of isolated points which rise abruptly above the 
Tertiary plain. The most important of these is Buffalo Peak, a point 
about 700 feet above the Park level, which measures only 300 or 400 feet 
across the flat summit. The specimens collected from all these basaltic 
exposures are rather uniform in petrographical habit. They are fine-grained, 
and, with the exception of macroscopical olivine and occasional augites, pos- 
sess no crystals recognizable by the naked eye. The microscope shows the 
usual combination of augite, plagioclase, and olivine, besides specular iron. 

Deep-seated fissures within the angle formed by the flexure of Park 
Range, a little south of the 41st parallel, have given vent, as before described, 
to an extensive outpouring of trachyte. Subsequently the same region was 
the theatre of volcanic activity in the period of the basalts. It has suffered 
severe erosion since the latest eruptions, and a great many of the attenuated 
ends and edges of the longer flows have been cut through, leaving only 
fragmentary outliers. The main basaltic mass is the high east-and-west 
ridge of the Elk Head Mountains, culminating in Anita Peak and Mount 
Weltha, and at the northern extremity in Navesink Peak. Outliers of the 
group stretch north of Little Snake River to Watch Hill and Bastion Moun- 
tain; and even south of the Yampa detached remnants of the southern flows 
have been observed. 

The most eastern exposure is a small outcrop directly in contact with 
the Archzean rocks north of Hantz Peak. The main body is about 20 miles 
from east to west and 24 miles along the longest axis through Navesink 
Peak and Mount Weltha. The basaltic country is for the most part very 
elevated, being from 8,000 to 10,000 feet above sea-level, and is well cov- 
ered with soil and dense woods, so that the exact age and character of the 
underlying sedimentary rocks cannot always be made out with certainty. 
Along the main exposure to the north and south it is clear that the basalts 
have broken through the sandstones of the Laramie or closing group of the 
Cretaceous. At the west end of the group, the long, interesting dike of 
the “Rampart” has broken through the Vermilion Creek Eocene; and from 


BASALTS. 655 


that region up to Navesink Peak the edges of the basaltic field are seen 
to rest on coarsely bedded, friable sandstones, which continue westward 
and define themselves as the Vermilion Creek group. At one or two 
places are obscure bodies of sandstones in the heart of the group, which 
may possibly be later members of the Eocene; but their nature and extent 
are too obscure to warrant any opinion. 

The basalts themselves have an exceedingly rugged surface, piling up 
in horizontal beds one above another, with plateau-like summits and broad, 
rugged spurs. They are interesting from a petrographical point of view, 
since two distinct types of the rock are here outpoured, namely, feldspar- 
basalt and nepheline-basalt. With the exception of the Elk Head region 
and the little group of the Kawsoh Mountains in western Nevada, all other 
Fortieth Parallel basalts belong to the feldspar group. Throughout the 
very great number of localities studied by us, not a trace of nepheline was 
found, except within the narrow areas of these two distant fields, and there 
the two types occur together, the nepheline group forming by far the 
larger flows at Elk Head. The ordinary feldspar-basalt, composed of 
plagioclase, augites, and olivine, occurs on the benches of Upper Little 
Snake River south of the valley, at Watch Hill on the north wall of the 
valley, also at Anita Peak, the elevated summit on the meridian of 107° 
15’, and again south of Yampa River near the forks. The rock on the 
benches of the Upper Snake is very peculiar, consisting of quartz, plagio- 
clase, augite, and magnetite, olivine being wanting. It has a dark, 
grayish-black groundmass of a rough habit, and bears a distinct likeness 
to the quartziferous trachytes of the neighborhood, which also have 
abundant augites. It rather expresses a transition between the augite- 
bearing, quartziferous trachytes and basalt, though from its habit and 
connection with the other basalts it has been here referred to the latter 
family. Considered as a basalt, it is interesting as an instance of the 
manner in which certain petrographical characteristics run through the 
different species of rocks of one locality. The trachytes of this region 
stand out with peculiar distinctness, on account of containing the large, 
cracked granules of quartz, while the groundmass is free from microscopical 
grains of that mineral, thus differing from the family of rhyolites. The 


656 SYSTEMATIC GEOLOGY. 


quartz grains of the basalt play a similar rdle. They are not constituent 
in the groundmass, but appear as distinct macroscopical secretions. Perhaps 
this occurrence throws light on the similar occurrence of quartz in the older 
diabases. Primary quartz, when present in our diabases, behaves as an 
irregular accessory mineral, bearing the same relations to the other con- 
stituents as in this quartziferous basalt. 

Across the valley of the Snake at Watch Hill is a coarse-grained 
dolerite, noticeable for the amount of dark globulitic base imbuing the 
groundmass. 

The plagioclase-basalt south of Yampa River, near the forks, belongs 
to the ordinary type of basalts, without distinguishing characteristics except 
the occurrence of haiiyne as an inclusion in the colorless plagioclases. 

The rock at Anita Peak consists of plagioclase, dark brown augite, 
olivine containing picotite, and an abundance of amorphous brown glass. 

The family of nepheline-basalts are broadly distributed over a large 
part of the Elk Mountain basaltic field, the following furnishing important 
examples: Fortification Peak, Navesink, Bastion Mountain, Mount Weltha, 
the ridge northeast of Hantz Peak, and the singular dike projecting westward 
from the main field, called the “Rampart.” Bastion Mountain, a detached 
outlier rising above the Laramie sandstones north of Little Snake River, is a 
flat-topped mass, about 1,200 feet of basalts being displayed upon its flanks. 
The rock is light-gray and very porous, the spherical cavities having a 
parallel arrangement which gives an almost schistose fracture. The inte- 
riors of the cavities are incrusted with yellowish calcite. In the rather fine 
groundmass, augite and olivine are distinctly seen with the unaided eye, 
and the microscope adds biotite, magnetite, nepheline, plagioclase, and a 
yellowish mineral referred by Zirkel to githite. Toward the western 
edge of the body are beds having very coarse pores underlaid by a greenish 
tuff somewhat resembling the palagonitie tuffs of western Nevada. The 
tuff encloses broken, angular fragments of scoriaceous basalt. 

Below the junction of Slater’s Fork with Little Snake River, upon the 
Cretaceous benches south of the stream, are two detached knobs of basalt 
which are doubtless outlying relics from the flows of Navesink Peak 
Navesink Peak itself has a distinctly conical shape. Its rock is a very dark, 


BASALTS. 657 


fine-grained body, of anamesitic texture. In this fine, uniform groundmass, 
dark, almost black augites and translucent olivines alone appear macro- 
scopically, the microscope detecting magnetite, biotite, nepheline, and a 
little plagioclase. 

Mount Weltha and the broad region around it, the highest elevation 
reached by the basalts in these mountains, yielded a rock extremely rich in 
olivine, associated with which the microscope shows magnetite, augite, 
nepheline, and sanidin in Carlsbad twins. 

One of the most interesting volcanic features in the neighborhood is 
the ‘‘Rampart,” a high, narrow wall of basalt extending four or five miles to 
the northwest from the western end of the basaltic flows of Mount Weltha. 
It is perfectly straight, and varies in height from thirty to sixty feet, having 
an average width of six feet. The sides are absolutely perpendicular and 
very smooth, and its summit is broken into crenelations, like the walls 
of a fortification. It is simply a dike which has resisted weathering, while 
the soft Eocene sandstones have been eroded away upon either side, and is 
altogether composed of basaltic columns arranged horizontally. In hand 
specimens the rock is light gray, entirely free from triclinic feldspars, rich in 
biotite, and shows fine augites, nepheline, and sanidins. 

Fortification Peak, which is a detached outlier, the relic of a former 
flow from Mount Weltha, is also of nepheline-basalt. It is rather coarse- 
grained, like some of the specimens from the slopes of Mount Weltha, and 
contains a little triclinic feldspar, augite, olivine, magnetite, and nepheline. 
A similar rock is observed on a ridge running northeast from Hantz Peak. 
It bears plagioclase individuals, nepheline, augite, olivine, and biotite. For 
a minute microscopical description of these rocks, the reader is especially 
referred to Volume VI., where Professor Zirkel has fully detailed their 
characteristics. 

As to the question which of the two types of basalt in the Elk Head 
Mountains is the older, we have not the data to determine; but the com- 
manding position and wide expanse of the nepheline-basalt make it prob- 
able that this was the later and more important eruption. 

Passing westward from the Elk Head Mountains, the broad area of the 
Green River Basin, the high Tertiary plateaus east of the Wahsatch, the 

42K 


658 SYSTEMATIC GEOLOGY. 


vreat range itself, and the eastern margin of the basin of Salt Lake are 
totally without basalts within the limits of our Exploration. Directly north 
of our map, on the prolongation of the trend of elevation of the Wahsatch, 
are basaltic bodies, which in passing northward increase in frequency 
until they connect with the great basaltic plains of the Snake. 

Here and there in Curlew Valley a few isolated knobs of basalt appear 
above the Quaternary, but the first basalt masses of any elevation are those 
in the region of Red Dome and Matlin. Red Dome itself is a noticeable 
mound of basalt, rising about 600 feet above the surrounding Quaternary 
slopes. The rock here has a dense, fine-grained groundmass of chocolate 
and reddish hues, usually quite compact, but at times highly porous. There 
are no macroscopical secretions other than plagioclase, augite, and occa- 
sional olivines. The extension of the rocks north of Red Dome shows 
sheeted tabular flows, with an inclination toward the south. 

West of this body the Quaternary of Duff Creek Valley covers the 
basalts; but on the western side of the valley they rise again, forming hills 
1,500 or 1,600 feet high north of Matlin Station. The distinct beds here 
incline 2° or 3° to the south and east, a bold ridge capped by domes and 
points defining the middle of the outflow. It is a black, brilliant, erypto- 
crystalline rock, without secretions visible to the unaided eye. 

The Ombe Mountains form one of those narrow, lofty ridges which 
rise out of the desert with no visible connection with any other range, con- 
tinue a few miles upon a defined trend, and suddenly sink again beneath 
the Quaternary plains. This peculiar orographical structure is due most 
unquestionably to great dislocations. Each one of these ranges may be 
considered as a block, more or less separated in altitude from its belongings. 
The sharp break at the northern end of the Ombe is accompanied by erup- 
tions of rhyolite and basalt, the basalt having broken out in immediate con- 
tact with the ends of the Palewozoie strata and flowed northward, over- 
whelming the greater part of the rhyolites. The inclination of the beds is 
to the north, and the general surface of the country rough and rugged, 
with a very slight accumulation of soil. The basalt has an extremely fresh 
look, the surface having not infrequently the ropy structure of lava-streams. 
The fracture of this rock under the hammer is characteristic of those basalts 


BASALTS., 659 


of very coarse groundmass and little or no glass base. It is a very dark 
gray, almost black, middle-grained rock, uncommonly rich in augite and 
unusually poor in olivine. The presence of a large amount of olivine or 
of glass base produces an easy fracture, with more or less vitreous lustre ; 
and the field habit of these rocks approximates to glassy andesites, Basalts 
poor in olivine and glass, on the contrary, present always very rough sur- 
faces and a dead, lustreless appearance. Indeed, an experienced eye detects 
the proportion of glass in a basalt almost as well by the fractures of the 
natural surfaces of the rock as by examining a thin section under the micro- 
scope. The more porous parts of the Ombe basalt show the ordinary 
scoriaceous, spongy condition, the pores being frequently filled with car- 
bonate of lime. An analysis of this occurrence is given in the table fol- 
lowing this section. While of exceedingly low specific gravity, it is 
correspondingly high in the equivalent of silica. In fact, it is the most 
acidic basalt of all the specimens analyzed by us, approaching some of the 
most basic of the augite-andesites. Aside from this locality, the eastern 
half of Map IV. has but two basaltic regions, both small and unimportant. 

One is the chain of basaltic outflows in the Ruby group, of which the 
most important exposure is upon the rhyolite field of the Beehives. Over- 
lying the rhyolitic tuff of the Beehives is a small field of fine-grained, dark- 
gray and black basalt which has flowed in a remarkable liquid condition, 
the entire formation being only 50 to 100 feet thick, and conserved on spurs, 
where its position has sheltered it from erosion. The beds are nearly hori- 
zontal, and along their eastern edge show some traces of underlying lime- 
stones, dipping slightly to the west. This basalt breaks with great freedom 
under the hammer, giving a curved, often conchoidal fracture, the surface 
having a peculiar greasy lustre. The fragments ring under the hammer 
like bits of bottle-glass. A few fragments of feldspars and grains of olivine 
are the only crystalline secretions visible, and these are but rare, the greater 
number of specimens showing no secretions at all. It is chiefly a dark- 
brown, acid glass, the true obsidian of basalt, and is the same noted by 
Zirkel as occurring at Ostheim, in the Wetterau, and at Sababurg, in the 
Reinhardswald. The most remarkable occurrences of this rock, however, 
are not the German but the great glass flows of the island of Hawaii. 


660 SYSTEMATIC GEOLOGY. 


South of Eagle Lake, from the detached outlying limestone west of 
Spruce Mountain, rises a basaltic dike forming a low connection between 
the limestone body and the Archean rocks of Humboldt Range. It is a 
fine black compact rock of andesitic habit. 

On the western side of the South Fork of Humboldt River two small 
basaltic knobs rise above the more recent Pliocene beds. This is an ordi- 
nary kind of porous basalt, rich in dark globulitic base, poor in olivine ; 
the augites almost wholly in the form of microlites, and plagioclases in 
slender pellucid tables. 

In the midst of the great trachyte mass on the eastern side of Pinon 
Range, east of Pinto Peak, one or two outflows of basalt through the 
trachytes have occurred. They are black, highly vesicular basalt, having a 
somewhat vitreous lustre, owing to the large amount of acidic glass which 
forms the abundant base of the rock. It is noticeable for the great size of 
the triclinic feldspars and its paucity in olivine. Farther south along the 
range, in the neighborhood of Fossil Pass, and south of Pinon Pass, are 
small outflows of basalt immediately contiguous to Devonian limestones. 

More important basaltic outbursts occur along the line of the eastern 
base of Pinon Range, in the field which has outflowed along the southern 
foot-hills of the rhyolite mass east of Pinon Pass, and, extending southward 
to Railroad Canon, has formed a broad volcanic connection between Pinon 
and Diamond ranges. Topographically, the form of this mass is that of a 
broad, low ridge having a few dominating dome-like summits. Lithologi- 
cally, the basalts of the group are very uniform, unusually rich in dark 
glass, poor in olivine, and rich in fine grains of augite. West of Pinon 
Range, lining the western foot-hills for twelve or fourteen miles, south of 
Cave Canon, is a series of tabular flows of basalt which slope toward Gar- 
den Valley. This table abuts directly against the Devonian quartzite of 
the Ogden group, presenting toward the range an escarped wall, while the 
main sheets dip toward the west at 3° or 4°. It is a hard, porous basalt, 
poor in glass and olivine. 

Pinon, Cortez, and Shoshone ranges and the Shoshone Mesa form a 
basaltic neighborhood which is of great importance. It will be seen that the 
outcrops, although locally determined by the strike of the ranges in which 


BASALTS. 661 


they occur, nevertheless extend themselves in a general line having a 
northwest trend. From Chimney Station, which may be taken as one 
point of the chain of outflows, the masses of Cortez Range, Whirlwind 
Valley, and the Shoshone Mesa form a suggestive chain of basaltic erup- 
tions parallel to the axial basalts of the Sierra Nevada. 

The body which margins the eastern side of Cortez Range from 
the neighborhood of Wagon Canon southward to the slopes of Mount 
Tenabo forms a continuous inclined plane of basaltic beds dipping from 
the range at gentle angles of 2° or 3° for about 30 miles. The line of 
fissure from which they outpoured cuts through the earlier volcanic rocks, 
and invades the Paleeozoic and granitic formations to the south. Flowing 
by gentle inclination down the eastern slope, it has been subsequently 
overlaid by the horizontal Pliocenes of Pine Valley and the later Quater- 
nary of Garden Gate and Garden Valley. One of the most interesting 
centres of this great outflow is where the rocks break through Carbon- 
iferous quartzites at Agate Pass. Here the lateral canons eroded in the 
basalts make excellent exposures of the surfaces and edges of the thin 
black sheets. Lithologically it is a fine-grained basalt, rich in brown 
glass base, poor in olivine, but with abundant colorless plagioclase, 
augite, and magnetite. Although the fine-grained varieties are most com- 
mon, there is a good deal of local change between the different layers 
as to the amount of crystals, the lower beds usually showing a greater 
abundance of microscopical secretions. Some of the very uppermost flows 
are as fine-grained as hornstone, breaking with a sharp, flinty, conchoidal 
fracture, and showing no macroscopical secretions. In occasional localities 
the reck is highly porous, the cavities being extended into long ellipsoidal 
pores. North and south of the summit of Agate Pass the size of these 
pores sometimes reaches a foot on the longer axis, and they are most fre- 
quently filled with masses of chalcedony or agate, from which the pass 
derives its name. These inclusions vary widely in character. Some of 
the large cavities are simply lined with a complete coating of flesh-colored 
and white chalcedony, presenting a smooth botryoidal surface to the hol- 
low interior, the entire lining being only about half an inch thick. Again, 


they are only partially filled with chalcedony or sharply terminated quartz 


662 SYSTEMATIC GEOLOGY. 


crystals. On the lower sides of the cavities and in the hollows of the chal- 
cedony there are frequently considerable deposits of delessite, which alsa 
plays an important part in the layers of agate inclusions. 

One of the most noticeable geological features of Shoshone Range is 
the reéntrant angle north of the Shoshone Peak mass. The high moun- 
tain body suddenly drops to a comparatively low level, and a deep bay of 
Quaternary enters the range, nearly cutting it into two separate parts. 
The northern part, which displays the characteristic Palaeozoic rocks 
around the western and northern margin of the body, is depressed far 
below the level of the Shoshone Peak mass. Basaltic rocks have broken 
out of a meridional fissure, flowing off eastward in gentle, inclined tables. 
An area of basalt is thus formed, measuring sixteeen to eighteen miles 
from north to south, and nearly as much from east to west. The lofty 
region is a plateau-ridge extending north and south, which from both 
extremities sends out to the northeast secondary ridges, that slope gradu- 
ally down to Humboldt Valley. Between these two ridges is the Quater- 
nary depression of Whirlwind Valley. The main and earlier flow is a 
fine-grained gray dolerite, with a moderate amount of grayish, globulitic 
base, and for crystalline secretions, plagioclase, augite, olivine, and mag- 
netite. Near the western escarpment of the main basaltic table a rude 
columnar tendency is noticeable in these gray dolerites, and in sections of 
the columns a tendency to develop globular forms by the flaking off of 
thin, concentric shales. Numbers of these doleritic balls roll down the 
slopes to the west, and might easily be mistaken for volcanic bombs, if not 
traced to their source. Through these crystalline dolerites break out sev- 
eral vertical dikes of a brilliant black basalt rich in acidie glass. These 
more recent basalts are very fine-grained, never showing any macroscopical 
crystalline secretions. The microscope discovers them to be made up of 
minute crystals of colorless plagioclase, fine globules of olivine, and yel- 
lowish-brown augite, the whole interspersed through a largely prevailing 
base of dark-brown acidic glass. Both the gray dolerite and the glassy 
basalt are more or less covered by a thin varnish of hyalite, which in some 
cases thickens, with a botryoidal surface, to a fourth of an inch. 


The broad field of basalt which covers the surface of Shoshone 


BASALTS. 663 


Mesa shows on the esearped edge of the table lands about 1,000 feet 
of basalts, in nearly horizontal layers of varying thickness. At Stony 
Point, the highest summit of the plateau, the basalts are rather light 
brown, with a mottling of green material. The rock is often vesicular, and 
is exceedingly fine-grained, no crystalline ingredients being visible to the 
unaided eye, with the exception of some sparingly distributed pale plagio- 
clases and grains of dark, pellucid quartz. The olivine is very dark, 
and approaches magnetic iron in appearance Even under the microscope 
augite is rare. The occurrence of quartz in a true dolerite entirely free 
from sanidin and possessing a normal percentage of silica, is certainly very 
remarkable; but the crystals must be considered as purely accidental acces- 
sory ingredients. The predominating rock of the whole Mesa is a normal 
dolerite, which is rather porous, the vesicles being filled with carbonate of 
lime. Coarse-grained varieties are most common, in which plagioclase, 
augite, and olivine appear as plainly visible macroscopical secretions, the 
microscope adding apatite and magnetite and an amorphous base. For the 
chemical analysis of this rock, see Table XII. 

At Jacob’s Promontory, associated with Carboniferous quartzites, 
augite-andesites, trachytes, and rhyolites, occurs a small field of basalt, 
forming the latest extrusion and the middle of the group of hiks. It is 
often quite vesicular, the cavities being more or less filled with carbonate 
of lime. The rock is made up of augite and plagioclase, with very little 
olivine. 

The few basaltic occurrences in the Augusta Mountains are of little 
importance. They are simply limited outflows of dikes that in each case have 
broken through rhyolite and are completely surrounded by thatrock. They 
belong without exception to the type with globulitie base, contain more or 
less olivine, and are of no geological interest except as emphasizing the 
earlier occurrences of augite-andesite in their neighborhood. 

In connection with the rhyolite which forms the great outburst of the 
Fish Creek Mountains, there is surprisingly little basalt. Only a few 
restricted outcrops occur along the northwestern foot-hills, where they have 
broken through the rhyolites and flowed toward the west in low, unim- 


portant tables. The chief geological interest of the basalts here, as already 


664 SYSTEMATIC GEOLOGY. 


alluded to under the head of rhyolites, centres in the flows of basalt which 
have come to the surface through true craters in the little rhyolite volcanic 
cones. Lithologically these rocks consist almost exclusively of feldspars. 
a fine, partially globulitic base, and large included crystals of sanidin. 
Neither in the hand specimens nor under the microscope is the base resolv- 
able into its constituent minerals. It is a fine, grayish-black, compact, 
uniform rock, in which only the large sanidins are visible. The occurrence 
of orthoclastic feldspars in the basalt, always rare, is of interest here since 
the basalts have come to the surface through highly acidic rocks, whose 
chief constituent is also sanidin. 

The small patches of basalt connected with the granite region between 
Ragan’s Creek and Rocky Creek, in the Havallah Mountains, have little 
petrological or geological significance. On the other hand, the body which 
lies along the eastern base of the range, in the region of Golconda Pass, is 
interesting as coming to the surface over rhyolites and as finding its exit 
near the abrupt termination of the great body of Triassic strata which 
make up the main mass of the range. 

A glance at the geology of Pah-Ute Range shows that its basalts are 
confined to the middle third, and consist of three independent masses: the 
Table Mountain body ; the thin, interesting outflows from dikes which have 
cut the various rhyolites of the Sou Springs group; and the large, little 
studied body which lies north of Granite Mountain, along the eastern base 
of the range. The Table Mountain and Sou Springs bodies are both easily 
related to the lines of weakness due to prior disturbance of the range. 
The former comes to the surface through rhyolites and in the immediate 
vicinity of the great diorite body of Chataya Peak, where a block of the 
Triassic strata has been ingulfed. The Table Mountain basalt body is 
one of the most interesting specimens of massive eruption in this whole 
region. It consists of nearly horizontal tabular sheets imposed one upon 
another, culminating in the long, level plateau ridge of Table Mountain, 
which has a height of fully 4,000 feet above the valley to the west. To the 
east it is escarped down for a thousand feet, where its lowest exposed beds 
are seen to rest upon rhyolite. Westward the declivity of the hills 
shows the edges of the heavy basaltic tables nearly down to the plain, 


BASALTS. 665 


where the bedding grows less distinct, and the body projecting northwest- 
wardly toward Buffalo Peak seems to be a relic of true flow. It is not 
unfrequently the case in the Great Basin that basaltic tables cap a high 
ridge, showing in their descent in every direction the escarped edges of hori- 
zontal beds. It is a little difficult in such cases to determine the loci of 
outflow. In the present instance it appears that the fissure which gave vent 
to the material was in the neighborhood of Table Mountain, that the viscous 
ejections flowed off in every direction, leaving nearly horizontal surfaces, 
and that subsequent erosion cut away the flanks of the body, exposing 
the edges of successive sheets. On examining the contact-planes of the 
different beds of basalt, they are sometimes seen to merge together with a 
continuity of material; and in others again there is a little voleanic dust or 
basaltic rapilli separating successive flows; and it is not uncommon where 
heavy beds are superposed one upon another for the vertical or highly in- 
clined jointings through a given sheet to cease at the plane ef contact with 
the next bed, which in turn may develop an entirely different set of joints. 
At the hills north of Sou Springs, basalts appear only as the limited 
outflow from a system of dikes. It is as interesting an instance as may be 
seen anywhere within our field of the direct superposition of basalt over 
rhyolite. While the underlying acidic rocks are notable for their glassy 
and porcelaneous groundmass and the almost total absence of crystallized 
material, these basalts represent the other petrographical extreme and are 
unusually free from the glass base so common in Nevada basalts, and in- 
versely rich in crystallized materials, of which well preserved augites, 
brilliantly striated plagioclases, and a little olivine form the bulk. The 
rock is sometimes slightly porous, but often very compact, with a bright, 
steel-eray color. In its geological habit there is a noticeable absence of 
the well defined horizontal bedding shown at Table Mountain, although 
the petrological characteristics of the two rocks are essentially identical. 
A large basaltic field which oceupies the eastern flank of the range north 
of Granite Mountain, like the Table Mountain group, is made up of distinct 
beds, which likewise dip toward the valley, having an easterly inclination 
of from 3° to 8°, with an average of 5°; a position which may not im- 


probably be referred to the original inclination of the outflow. The basalt 


666 SYSTEMATIC GEOLOGY. 


here reaches 3,600 feet above the plain, and is deeply scored by canons 
which show a great thickness of material. It bears very close resemblance 
to the other basalts of the range, and, like them, is characterized by a large 
amount of crystalline minerals and little glassy material. The northern 
half of West Humboldt Range may be considered as an isolated block 
displaced upwardly from its direct geological connections. Its margin is 
more or less marked by narrow exposures of basalt, which are always at 
the junction of the foot-hills with the neighboring desert valleys. They 
are comparatively unimportant, and are only noticeable for the fact that 
as a group they repeat the characteristics of the Pah-Ute basalts as to 
the absence of glassy or globulitic material and the prevalence of defined 
crystals. Asa rule, the West Humboldt basalts are of an exceedingly fine 
grain, olivine alone being visible to the naked eye. The basalt of Eldorado 
Canon is noted by Zirkel as a rather rare rock, being entirely crystalline, 
with olivine as the sole macroscopic constituent. The microscope reveals 
plagioclases and augites, the latter remarkably well crystallized and show- 
ing a zonal structure; the olivines contain picotite. 

Of the basalts of the southern half of the range, those which lie 
southeast of Oreana are the outflowing of northwest-southeast dikes, 
which are seen in the form of bedded masses inclining to the east. They 
are chiefly a very vesicular rock, whose pores are for the most part filled 
with a soft, crumbling calcite not improbably derived from the adjacent 
limestones, the basaltic material being quite undecomposed. 

Directly east of Lovelock Station, the foot-hills of Humboldt Range 
are again overflowed by basalts which here have broken through about on 
the line of junction of the steeply inclined Triassic series and the gently 
disturbed Miocene beds. The basalts, which are dark, vesicular rocks, 
rather finely crystalline, have steel-gray and reddish-gray colors, and show 
to the unaided eye only olivines. They are specially interesting geologi- 
cally, since they oceupy a shallow, saucer-like depression eroded on the 
edges of the Miocene beds. It is noteworthy that these Miocene beds were 
upheaved prior to the rhyolite eruptions, that the stratified series them- 
selves are largely composed of trachytie material rearranged in a fresh- 


water lake, and that between their uptilting in connection with the rhyolitic 


BASALTS. 667 


disturbances and the appearance of the basalts, there has been a very con- 
siderable erosion. This would indicate for this region quite an interval 
between the rhyolitic and basaltic periods. Sucha period of volcanic quiet 
is further indicated by the fact of the basalts frequently occupying valleys 
and depressions in the rhyolite, which were evidently not accidents of 
original structure, but decidedly the effects of erosion. No special study 
has been given to the scattered masses of basalt which have come to the 
surface through the Triassic beds to the south, and these minor basaltic 
masses are of no special interest, unlike the one at the western end of the 
Mopung Hills, which is an excellent sample of the superposition of basalts 
over rhyolites. 

Montezuma Range, one of the most heterogeneous pieces of geology 
in the whole region, has three prominent basaltic areas. The ancient 
Archean mass which culminates in Trinity Peak is cut off northward and 
southward by sharp depressions. That at the north is occupied by low, 
gently rolling hills of soft Miocene beds, through which a heavy dike of 
basalt has burst up, forming a well defined ridge having a northwest-and- 
southeast direction and rising above the level of the desert and of the 
Miocene formations from 1,000 to 1,200 feet. At the southern end of the 
Archean body is another topographical depression in which is an enormous 
flood of heavy bedded black basalt cutting diagonally across the range, 
having a northwest trend parallel with the Indian Pass body. 

The minor occurrences of basalt margin the ends of the granite spurs 
which border on Humboldt Valley in the region of Antelope Peak. The 
southern termination of the range shows a large number of small basaltic 
eruptions. Coming to the surface through the rhyolites, and where the two 
rocks are exposed by modern degradation, there is ample evidence of con- 
siderable erosion of the rhyolites prior to the outpouring of basalts. Phys- 
ically, the two northwest-southeast basaltic bodies bordering upon the older 
rocks in the middle portion of the range are essentially a bedded series. 
They are exposed in deep canons and show not less than 1,200 or 1,500 
feet of superposed beds. On the contrary, the basalts of the southern end 
of the range are irregular masses, covering ridges or extended as in lava 
streams. When closely examined, these latter deposits, especially those in 


668 SYSTEMATIC GEOLOGY. 


the mouth of Bayless’ Cafion, are indeed bedded, but on a smaller scale and 
with less conspicuous planes of division than the broad masses to the north. 

The Montezuma basalts show a very considerable variety of texture 
and color, passing from dark chocolate-brown into steel-gray and certain 
greenish shades, due to the prevalence of olivine. As a whole, they have a 
common likeness, due to the abundant presence of glassy and globulitic 
base, giving them in general a strongly vitreous lustre upon the newly broken 
surfaces, and producing in extremely glassy varieties an almost flinty frac- 
ture. In this respect they offer a complete contrast to the neighboring 
basalts of Humboldt and Pah-Ute ranges. The microscope shows this 
family of basalts to be extremely poor in large, well defined augite crystals, 
that mineral almost always occurring as minute microlites or as small shat- 
tered prisms, always inferior in size to olivine and in crystalline finish to 
plagioclase. The olivines in the basalts near White Plains are charac- 
terized by an abundance of picotite. In the same rock are associated 
remarkable structures of magnetite crystals. 

The northwesterly trend of the two large basaltic bodies of Montezuma 
Range is noteworthy as belonging to a series of northwest fissures, which 
become evident in approaching the Sierra Nevada. 

The granites of Granite Point are largely overflowed by powerful 
outbursts of gray and black, more or less vesicular basalt, which is seen 
to overlie the rhyolites and to slope toward the desert to the east, with a 
defined bedding. At Lovelock’s Knob, also, the granite and overlying rhyo- 
lite are broken through on the north base of the hills by a small overflow 
of basalt, which is a close-grained, half glassy rock, containing no macro- 
scopical individuals except olivine, breaking with a distinctly conchoidal 
fracture and displaying upon fresh surfaces the characteristic vitreous lustre 
of a basalt rich in glass base. Similar but somewhat less glassy basalts are 
found in small, detached outcrops north of Brown Station. This little 
group partly breaks through and overlies the rhyolites of the main range 
and partly rises as low, detached outliers, lifted above the Quaternary of 
the desert. These latter are extensively incrusted by thinolite, the remark- 
able pseudomorphic tufa of Lake Lahontan. 


The little group of Kamma Mountains geologically repeats many of 


BASALTS. 669 


the leading conditions of Montezuma Range. The basalts, however, of 
which there are two separate groups, come to the surface at the highest 
parts of the range and are in contact with the older Archzean formations, 
and at the same time break through and overlie the rhyolites. The group 
in the region of Aloha Peak is surrounded on all sides by rhyolites, except 
to the west, where the Archzean mass forming the east wall of Crusoe Cation 
rises into contact with the capping basalt. Generally the rocks here are 
dark and vesicular, their only crystalline secretions being white specks, 
which the microscope shows to be plagioclases that have suffered more or 
less decomposition. The groundmass is finely crystalline, and there is a 
high proportion of amorphous, glassy base. They are also deficient in 
augites. At the northern point of the range, in Grass Canon, the high sum- 
mits are again of basalt, and have come to the surface and piled themselves 
up upon lofty, rugged masses of rhyolite. Not far from the mouth of Grass 
Canon the basalts are of well defined columnar structure, the prisms lying 
horizontally. The material is vitreous, with sharp, conchoidal fracture, the 
eye discerning abundant plagioclases and the microscope adding augite and 
olivine in an amorphous, globulitic base. The rocks to the south of Basalt 
Peak, near the head of Grass Canon, are heavy bedded, dark, richly 
augitic types, underlaid by basaltic tuff, which is of a dark-olive color and 
an earthy, crumbling texture, composed of dark-brown augite and shat- 
tered crystals of plagioclase, associated with abundant, very acidic brown 
glass. The latter fails to gelatinize when treated with acids, and has 
received the designation from Professor Zirkel of hyalomelane tuff. There 
is a much higher proportion of acidic glass than in any of the solid basalts 
of the region. It was doubtless an accumulation of volcanic sands blown 
from some neighboring orifice; the angular character of the minute glassy 
fragments closely resembling that of the glassy basaltic sands observed by 
the writer upon the Hawaiian Islands. 

The remarkable level plains of Mud Lake Desert, in the northern 
portion of Map V., are surrounded on every side by more or less abrupt 
mountain masses rising like islands above the Quaternary sea. One of the 
most interesting of these is a low, rugged group of hills known as the Black 
Rock Mountains, which invades the desert from the north and lies directly 


670 SYSTEMATIC GEOLOGY. 


west of the sink of Quinn River. Here is a mass of hills made up within 
the limits of our map entirely of rhyolites and basalts, the latter occurring in 
a series of ridges, presenting rather sharp, abrupt escarpments to the west and 
a gentle declivity to the east. It is not certain whether this position is due 
to flow or to tilting. The anomalous position of the rhyolites overlapping 
the base of the basaltic slopes gives rise to the idea that the whole region has 
suffered sharp dislocation since the basaltic period. At the extreme southern 
point of the range is a conspicuous basalt mountain rising 500 or 600 feet 
above the white desert. Examining the hand specimen, the rock is seen 
to have a very fine-grained, greenish-gray groundmass, in which plagio- 
‘lase and amber-brown augites are conspicuous. Just north of this rock 
was collected a coarse dolerite in which the plagioclase crystals are an inch 
long. The augites also are a quarter of an inch in diameter, and stand out 
very roundly above the slightly vitreous groundmass. The true dolerites, 
always rare in the Fortieth Parallel area, occur here in considerable variety. 
The feldspars are always better crystallized than the augites, the hand 
specimen indicating little or no glass base, and the microscope revealing 
only a small proportion of globulitic material. The prevailing colors of the 
dolerite are dark, greenish-gray, weathering to dark-brown and black. 
Near Hardin City, overlying the white rhyolitic breccias, is a series 
of basalts, the uppermost beds on the top of the cliffs being fresh, black, 
and lustrous, having an exceedingly resinous surface. The augites are 
shown by the microscope to be pale colored and few, often occurring only 
as microlites. Unlike the neighboring dolerites, they are entirely wanting 
in olivine, and the magnetite is highly altered, resulting in yellowish-brown, 
hydrated matter. Beneath these less altered basalts is a series of highly 
porous and very decomposed beds; the extreme results of decomposition 
being an earthy, green, spongy seladonite, and a waxy material consisting 
of alumina and silica, with a small percentage of alkalies and iron. Besides 
these earthy, green inclusions, many of the cavities are lined with botry- 
oidal chalcedony, and others again have a botryoidal surface within their 
cavities, which is varnished over with a brilliant glaze of iron oxyd. 
The neighboring hills abound in geodes and ellipsoidal pebbles of chal- 


cedony, which are the sole relic of decomposition, all the basaltic mass 


BASALTS. 671 


having passed through the seladonite phase, ending in disintegration and 
erosion. 

This little group of hills is still further noticeable for the occurrence 
of two forms of basaltic tuff—one an earthy-looking mass which under the 
microscope is seen to consist altogether of partially decomposed augites and 
plagioclases associated with an enormous amount of acidic glass, which 
remains almost totally undecomposed, in sharp angular, wedge-like chips. 
There is little or no cement to hold these together, and like the similar tuffs 
of Pah-tson Range they are doubtless a simple accumulation of rather 
acidic basaltic sand. The other is a true palagonite-tuff, which receives 
special mention from Professor Zirkel in Volume VL, page 275. Unlike the 
palagonite of other Nevada localities, it is directly connected with basaltic 
eruptions, never having been rearranged and enclosed in the Tertiary 
strata; all the rest being distinctly stratified members of a conformable 
Miocene series. As has been seen, when treating of the Truckee Miocene, 
the other palagonitic beds altogether antedate the period of basaltic eruptions, 
and we have been led by their higher acidity to refer them to the augite- 
andesites with whose date of eruption the stratified palagonites sufficiently 
well agree. 

Both the Black Rock palagonites, which are so intimately associated 
with the main basaltic eruptions as to be considered their dependent, and 
the Miocene stratified palagonites, must have undergone their characteristic 
metamorphism entirely without the presence of marine waters. If we are 
right in dating the Black Rock palagonites with the basaltic eruptions, there 
have been clearly two palagonite-making periods in Nevada. 

West of the great Mud Lake Desert, and occupying the northwestern 
corner of our map, is the escarped edge and the broad, undulating surface 
of a great basaltic plateau The desert lowlands are walled in in that 
direction by a rampart of basalt from 1,200 to 1,500 feet in height, 
which either rises in steep slopes, as along its southern portion, or recedes 
in broad plateau steps, as at the north. Reaching the summit of this as- 
cent, the country stretches west and north for a great distance in a gently 
undulating plateau, altogether of basalt, known as the Madelin Mesa. It 
is the beginning of that great series of basaltic fields which covers so large 


672 SYSTEMATIC GEOLOGY. 


a portion of northern California, eastern Oregon, and Idaho. South of the 
Fortieth Parallel, basaltic areas are never very wide. No great province of 
the Cordillera is wholly free from occasional exposures of basalt, but there 
are elsewhere none of those enormous sheets which characterize the region 
to the north. In riding over hundreds of miles of this northern country, 
whose surface is made up of apparently continuous sheets of basalt, one 
has constantly forced on him the question, whether these broad fields are 
sheets which have come to the surface and flowed out, covering wide areas, 
or whether the whole country beneath them is riven with basaltic dikes, 
whose overflows have mingled or piled one upon another, forming a gen- 
eral plain. An examination of a considerable part of Shoshone or Snake 
River, which flows for over a hundred miles through a sheet of basalt, has 
inclined me to the belief that, in some cases at least, the basalts have 
flowed for a very long distance. 

For many miles the great section of the volcanic Snake plain, as 
shown by the cafion, consists of a trachytic underlying body, whose sur- 
face indicates hills of several hundred feet in height, capped by a series of 
thin, superposed sheets of basalt, which for very many miles received no ad- 
dition by new eruptions; long distances of the trachytic wall showing no 
volcanic dike whatever. So, too, in Cascade Range, the long basaltic 
streams which flow down the western slope have frequently received no 
reinforcement by new dikes throughout the whole length of their flow, 
which often exceeds fifty miles. The power of basic lavas to retain their 
heat, and consequent fluidity, making exceedingly long flows, is well 
known, and there seems to be no strong reason to doubt that these great 
mesas, like that of the Madelin and of the Snake plain, may be simple 
sheets spread out over a country which itself contains few or no basaltic 
dikes. 

A considerable stretch of granite ranges, noticeable for their Tertiary 
eruptive rocks, separates the northern and southern basaltic regions of 
Truckee Range. Along the western foot-hills of the northern terminus of the 
range, the elevated granite mass is edged by low hills of basalt, which are 
of no considerable orographical importance, but the southern region and the 
angle between the railroad and Truckee River from Natche’s Pass to Desert 


BASALTS. 673 


Station, offer a most interesting exhibition of basaltic rocks. The moun- 
tain ridge, at an elevation of 4,500 feet above the adjacent valleys, is for 
the most part covered with heavy accumulations of basalt. That the 
entire body of this elevation is not made up of basalts, is clearly seen by 
the points of diabase and rhyolite which rise above its surface, and the 
broad mass of metamorphic Triassic strata and diabases which interrupt 
the basalts in the region of Miner’s Canon. Along the southern margin of 
the basaltic foot-hills are innumerable highly scoriaceous, rudely globular 
fragments of basalt, which lie disposed about on the desert far from any 
line of drainage, suggesting by their appearance and isolation the idea that 
they are volcanic bombs. The extremely diversified voleanic topography 
is chiefly made up of irregular ridges and spurs, which when studied in 
detail are found to be composed of rather thinly bedded, dark basalts, each 
ridge having its bed inclined down both flanks, after the manner of an 
anticlinal. In fact, a section of each separate ridge or prominent spur 
would show a clear arched structure of voleanic flows. Between succes- 
sive beds there is a little débris or dividing matter. Occasionally large 
steam-cavities, evidently made by molten basalt rapidly overflowing a 
pool of water, are seen. Some of these steam-cavities are eight or ten feet 
in diameter, and the interior walls are remarkably even and smooth. It is 
interesting to observe the basalts in immediate contact with the earlier 
diabases, the two augitic rocks are so entirely different in geological habi- 
tus. The older rocks uniformly occur as a structureless, massive body 
showing none of the bedding or evidences of flow which the basalt every- 
where indicates. The arched structure of all these basaltic ridges is un- 
questionably to be accounted for as the direct overflow of dikes. The 
continued eruption through long, vertical dikes has effected the piling up 
of the centres of the ridges, while the sheets of molten material poured 
down either side. As the operation continued, the centre grew faster than 
the flanks; and for the uppermost beds the result was quite a steep arch. 
In the immediate neighborhood of the diabase hills, the lower basalts, 
representing the earliest flows which are exposed, are of a highly erystal- 
line type. They are rich in olivine and poor in augite. The olivines 
change into a reddish-brown material, not unlike the brown serpentine of 
43 K 


674 SYSTEMATIC GEOLOGY. 


the diabase olivine. This type of rock is extremely rare here, and no- 
where appears among the more important and later eruptions. The char- 
acter of these is somewhat peculiar. Crystalline minerals are reduced to a 
minimum, the microscope showing a considerable number of twin plagio- 
clases and a small amount of sanidin, which, however, is large for basalts. 
The augite is rather pale and never over-plentiful, and the olivine shows at 
times a slight alteration into serpentinous material. Picotite is not infre- 
quent in the larger olivines. But the most remarkable characteristic of the 
basalt is the very large amount of acid glass which fails to gelatinize under 
long digestions in acids. Nearly all the basalts of this neighborhood, cer- 
tainly all the later eruptions, have a peculiar flinty fracture, and although 
the steel-gray or brown surface may in extreme sunlight show a brilliant 
steely lustre, due to minute crystalline ingredients, yet the resinous lustre 
of the highly glassy rocks predominates. It is interesting to note that in 
the presence of this highly acidic glass the more acidic feldspars also occur. 
The average proportion of silica, fully 55 per cent., as determined by tests, 
would indicate a relation with the augite-andesites were it not for the 
normal proportion of olivine, which at once removes the rock from the 
andesite family. The basalts of this particular region haye been fully treated 
in Volume VL, page 233 et seq. 

The importance of the basalts of the Kawsoh Mountains is due rather 
to their geological connections than to any special petrographical interest. 
They have come to the surface through cracks and fissures in upturned 
Miocene beds, and have poured over a surface which was much modified 
by erosion after the uplift of the beds and before the outpouring of the 
basalts. 

In the Miocene section of Chapter V. of this volume is discussed the 
evidence as to the age of these lacustrine Tertiary beds, evidence which has 
led quite conclusively to their Miocene date. Across the little valley which 
separates the Kawsoh from Montezuma Range, at the foot of the latter hills, 
near White Plains, these Tertiary beds are seen to be invaded and disturbed 
by rhyolitie eruptions. The beds themselves are largely made up of ande- 
sitic and trachytic tufts, yet the trachytie rocks which occupy the northeast 


corner of Kawsoh Range would seem, from their relative position to 


BASALTS. 675 


the Tertiaries, to be more recent. It is probable, therefore, that the 
upheaval took place near the close of the age of trachytic outflows, an 
enormous amount of ejecta being represented in the rearranged Tertiary 
beds. 

In the superposition of basalts at White Plains above the rhyolites, 
and in the Kawsoh Mountains above the well defined Miocene series, 
we have a very direct piece of evidence as to the real geological 
age of the basalts. The basalts of the Kawsoh group have a rugged 
surface rising to 1,200 feet on the southwestern elevations. The ridges and 
hills show a very great variety of rough, lava-like surfaces, and at the 
northeastern limit of the hills, near Mirage Station, are seen some evidences 
of considerable dislocation since the basaltic flow. There are masses of 
Tertiary with a tilted cap of basaltic beds at an angle evidently higher 
than that of natural flow in position, which cannot readily be accounted for 
otherwise than by their direct uplift. Near the northwest base of the hills 
are hot springs, interesting from their proximity to the basalts and from their 
considerable tenure in boracic acid. Petrographically, these basalts belong 
to the family just described in Truckee Range. They have always a low 
proportion of defined augite crystals, whose colors are usually delicate and 
pale, with considerable olivine. But rather the most characteristic feature 
is the abundance of globulitic, half glassy, or purely glassy base, which 
occurs either as inter-wedged, cuneiform inclusions, or as a true ground- 
paste. Scoriaceous and finely porous rocks are not uncommon. Among 
the voleanic bombs found on the desert along the western margin of the range 
are many dark, almost brick-ved globes of basaltic scoria, the innumerable 
pores lined either with a pale-lilac or a brick-red varnish-like coating. Some 
of these large blocks, one or two feet in diameter, are found almost as light 
as a sponge. 

Near the south point of the group a rather compact, fine-grained basalt 
was found, in whose pores Professor Zirkel discovered microscopical tridy- 
mite in hexagonal lamine precisely as they occur in rhyolites and trachytes. 
The occurrence of infusorial silica in such enormous masses in the very 
beds through which these basalts have come would seem to furnish a near 


source for foreign silica, and to indicate that the basalt during its passage 


676 SYSTEMATIC GEOLOGY. 


up a fissure through the soft, infusorial silica might easily have taken up 
portions of the earthy material, and by the influence of heat and pressure, 
together with some moisture, have produced the hexagonal tridymite. 

The limited triangular group of hills south of Deep Wells repeats the 
geological conditions of the Kawsoh. It is a body of basalt superposed 
upon the upturned edges and inclined backs of dislocated Miocene strata. 
The basalts themselves are almost uniformly of the variety which is poor 
in developed crystals of augite and rich in amorphous globulitic glass. 

From far to the south of the limit of Map V., Virginia Range, up to 
its northern extremity, is at various points covered by local sheets of basalt 
which, as usual, constituted the latest of the great series of Tertiary erup- 
tions. In their physical mode of occurrence the basalts of Truckee Canon 
are of interest, since their relation to the underlying trachytes and 
rhyolites shows that the line of depression where the river traverses the 
Virginia mountain-range was a pre-basaltic gorge. In the river bottom 
near Clark’s Station the basalts overlying rhyolite and trachyte descend 
to the water-level. The high hills which rise to the south of the cation are 
entirely covered with great sheets of heavy bedded basalts inclined toward 
the river, showing that the flow of the repeated eruptions was down the 
slopes of preéxisting trachyte mountains toward the bottom of the canon. 
Post-basaltic erosion has certainly cut away the base of the basalt slopes 
which no doubt formerly filled the entire canon bottom. The vents from 
which these basaltic flows must have come are far up on the southern hills. 
South of Clark’s Station an important canon opens into the range, display- 
ing basaltic beds for a thickness of perhaps 2,000 or 3,000 feet. 

North of the river the west portion of the range is made of rhyolites 
and trachytes, with a long meridional basaltic flow which covers all but the 
higher portion of the range. The petrological characteristics of these 
basalts are considerably varied. The rocks upon the south base of the 
upper portion of the canon are composed of a rather coarse-grained ana- 
mesite rendered peculiar by the absence of olivine and the presence of a 
brownish-gray globulitic amorphous mass. The flows which reach nearest 
to Truckee River a few miles above Clark’s Station are extremely fine-grained 


passages of the same anamesitic type. North of the canon all the basalts 


‘sisXquuv 
jo toquinyy 


~ 
Ke) 


I 


168 


169 


170 


171 


TABLE OF CHEMICAL ANALYSES. XII—UNITED STATES GEOLOGICA y 


Basalts, 
25 Locality. Analyst. Si AY | Fe | Fe | Mn | Ga | Mg | Na we || tye 
5 i 
= } 
167 | Summit of Elkhead, Geodetic Point | R. W. Woodward | 48.60] 15.78] 3-22) 7.21 
25.92 7:35 0.96 1.60 
cc Ws Ww re 48.46] 15.61] 3-44] 7-21 PO® 0.11 | 1.30 
25.84 7:27 1.03 1.60 ie) he a |e 
; 
168 | Edge of cliff, Stony Point Range - iB Baits) "7-95 Bet 5.88 tr. Toes 6.99 ae 1.03 
25.81 +3! o. 1. so. 2.87 2-79 0-74 0.17 
t 
rs ae ss ce 48.38] 18.45] 2.12] 8.90] tr. | 10.32) 7.02 2.73 1.03 
25.80 8.59 0.64 1.97 Oa 2.94 2.81 0.70 0.17 
169 | Buffalo Peak, North Park - - - # 49:04 Hast ai 770) athe 7-11 aa oy? 2.11 
26.15 44 0.81 1.71 tae 2.03 1. . 0.35 
J 
SJ ‘ = fe 49.01 | 18.32] 2.63 2.18 
26.14 8.53 9.79 0.37 
170 | Three miles Northeast of Wads- oe 94.) 17-0 2: 261 
worth, Nevada. 5335 es ae a 
a i ey es 53:98] 17:05] 3:00 2.23 
28.78 7-94 0.99 0.38 
171 | Ombe Range, Nevada - - - - Ws 54-80] 17.58| 0.97 1.16 
29.22 8.19 0.29 | 0.19 
¢ é De ed | a 54-79| 17-59] 0-94 1.16 


2.19 


TA] 


*sis{peue | 
Jo xoquny | 


us) 


TABLE OF CHEMICAL ANALYSES. XIIL—UNITED STATES GEOLOGICAL EXPLORATION OF THE 


DIABASES AND DIORIPES. 
Diabases. 


= a 
2 Locality. Analyst. Si At te | Fe | Mn! Ca 2 
E Ey 
Zz | |. | a 
172 | Diabase Hills, Northeast from Wads- | R. W. Woodward | 54.52] 19-10] 2.83] 5.89) tr. | 7-25 |i Ti On trace] | 
worth, Nevada. 29°07 0 a9 coin anaes Regt) it~, Gia y 
| i 
| 
« « « 54:80] 19.10} 2.67) 5-90] tr. | 7.26 Aor three) 
29.22 9.00 0.80 1.38 - 2.07 
Diorites. 
173 | Eldorado Outcrop, Mount David- | RW. Woodward| 56.71] 18.36] . .| 6.45 | 6.11 
| son. go.zq | 8.55 | «|| sxeagi| - cellmaxeral 
“ « «“ “ 56.58 18.20 5:99 
go.17 8.48 1-70 
174 | Agate Pass, Shoshone Range - - 5 58.14} 16.68 oe 5-62] tr. 6.00 
3i.co 777 < 1.25 eare 1.71 
Ks Be - = ie 58.24] 16. BS sion: 5:59) tr 
31.05 7-85 aa 1.24 od 
175 | Three Peak Mountain, Shoshone i 60.20] 18.55] . .| 4.37) tr 
Range. 32-10 8.64 io 0.97 tp ts] 


——— 
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ANALYTICAL GEOLOGICAL MAP OF Siem 


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KPILORATION OF EVES POUR IIENIMED TAURVACISIEVE Li ceee Vill 


ROCKS 


CANIC 


mate Miles w one Inch. 


DACITY [ ANDESITE Esa QUARTZ PROPYLITE | PROPYLITE (esl 


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BASALTS. 677 


are of the ordinary feldspar variety, and poor in the globulitie or glassy 
base. The triclinio feldspars are correspondingly large, and the olivines 
small. 

At the entrance of the canon, opposite the andesite flows which form the 
southern hills, is a body of sanidin-trachyte overflowed by black vesicu- 
lar basalt which is for the most part a compact, fine-grained rock with few 
macroscopic crystals and little globulitic base. The microscope shows it to 
be made up of abundant triclinic feldspars, extremely minute olivines, a 
high percentage of magnetic iron, and occasional apatites. 


SECTION Vi: 
CORRELATION AND SUCCESSION OF TERTIARY VOLCANIC ROCKS. 


QuanTITATIVE CHEMICAL Retations.—Regarded from a chemical point 
of view, the Tertiary volcanic rocks of the Fortieth Parallel conform in 
general to the law of Bunsen. <A reference to the tables of chemical 
analyses given with the section devoted to each rock will disclose the fact 
that there are no wide deviations from the numerical relations of constit- 
uents as laid down in that law. Further, a comparison with the published 
analyses of Roth shows a close parallelism with the type-rocks of the Old 
World. 

Classing the various species by their silica equivalents, we have: 1. A 
series of acidic products—quartz-propylite, dacite, quartziferous trachyte, 
and rhyolite. 2. A group of chemically mean products—hornblende-propy- 
lite, hornblende-andesite, and the peculiar group of hornblende-plagioclase- 
trachyte. 3. A basic family composed of augite-propylite, augite-andesite, 
augite-trachyte, and basalt. 

When we come to examine into the quantitative relations of these three 
chemical groups, it will be seen from the foregoing description of localities 
or from analytical Map VII. accompanying this chapter, that the acidic 
products as a whole are enormously in excess of the basic products, and 
that they are almost equally in excess of the rocks of mean constitution. 
Certainly eight tenths of the basic ejections are of basalts, the latest of the 
whole series. Recalling that the basalts have in a great majority of cases 
outpoured from the vents of former acidic eruptions, and generally partially, 
sometimes wholly, covered the early siliceous rocks, and that, in spite of this 
considerable burial, the actually exposed area of the highly silicated rocks 
is still far in excess of the basic ejecta, we see at once that the rocks of 


Bunsen’s normal trachytic magma are quantitatively very far in excess of 
78 


CORRELATION OF VOLCANIC ROCKS. 679 


the normal pyroxenic magma Furthermore, they far exceed the sum of 
the basic and mean rocks. 

Having seen a very considerable portion of the voleanic field of the 
West from the Mexican line to Washington Territory, I am convinced 
that this quantitative law holds good for the whole Cordilleras of the United 
States. A geological map alone, without a correct knowledge of the under- 
lying rocks, conveys but a crude idea of the actual and relative amounts of 
extravasation of the various species. Tor instance, the great basaltic plain 
of the upper Shoshone Valley on a map of ordinary geographical scale 
could only be laid down as a continuous field of basalt, but an examination 
of the canon walls of Snake River, and the mountain flanks bordering the 
basin, shows even there a probable quantitative predominance of acidic 
trachy tes. 

So, too, all we know of the great chain of massive eruptions and vol- 
canic cones which have built up their prodigious floods of ejecta along 
the axial region of the Sierra Nevada and Cascade ranges, in like manner 
shows that the acid rocks enormously predominate. An erroneous impres- 
sion may also be derived from geological maps, from the well known prop- 
erty of pyroxenic species to retain their fluidity far longer than the trachytic 
type, and in consequence to flow out in thin sheets, covering more area 
than an equivalent amount of acidic rock. This property of retaining 
fluidity is obviously in direct accord with the actual temperature of fusi- 
bility of the pyroxenic magma, which can retain fluidity at a considerably 
lower temperature than the acidic magma. Yet it is doubtful whether this 
property alone is enough to account for the great difference of habit of flow 
between the two opposing types, and it will be argued in the sequel that 
the pyroxenic rocks in general have reached the surface in an actually 
hotter state than the acidic ones. 

In spite of the enormous basaltic fields of Oregon and Washington 
Territory, all the great cones thus far examined are trachytic, with the 
exception of two which are of andesite. Anda very great number of 
exposures in the region of the broad basaltic areas show heavy underlying 
acidic bodies like that of Shoshone Plain. To all these must be added the 
vast series of acidic tuffs bedded in the Miocene and Pliocene lakes of 


680 SYSTEMATIC GEOLOGY. 


Nevada, Utah, Idaho, Oregon, and Washington, besides the Miocene vol- 
canic acid mud-beds exposed in the coast series of rocks through Oregon, 
California, and Mexico. Taken as a whole, there is without doubt a very 
great predominance of acidic rocks. 

In the Fortieth Parallel area the various species, beginning with the 
most abundant, stand in the following quantitative order: 


. RHYOLITE. 
. BASALT, 
TRACHYTE. 
. ANDESITE. 
. PROPYLITE. 


Po he 


or 


A comparison of the quantitative relations of the augitic, quartzose, 
and mean products of the last three groups shows in general terms a similar 
result. 

Quartz-propylite exceeds normal hornblende-propylite, and that has a 
far greater volume than augitic propylite. 

Dacite and normal hornblende-andesite far outweigh augite-andesite. 

So, too, true augite-trachyte is much rarer than sanidin-trachyte and 
comparatively of unimportant mass. 

Whether, therefore, we view the whole series of volcanic products 
together, or whether we study only separate groups, the pyroxenic magma 
is quantitatively inferior. 

A detailed quantitative scale would therefore be: 


1. RHYOLITE. 

2. BASALT. 

3. TRACHYTIH.—a. Sanidinic and Quartziferous. 
b. Hornblendic with much Plagioclase. 
c. Augitic. 

4. ANDESITE.—a. Dacite. 
b. Hornblendic. 
ce. Augitic. 

5. PROPYLITE.—a. Quartziferous. 
b. Hornblendie. 
c. Augitic. 


CORRELATION OF VOLCANIC ROCKS. 681 


In this expression the augite member always fails to equal the mean or 
highly acidic type member of the group, with the single exception of basalt, 
which has no heretofore recognized acidic correlative. In the succeed- 
ing section I shall attempt a somewhat new feature of classification, in 
which basalt and rhyolite will be thrown into a generic relation, and it 
will be argued that rhyolite is the acidic member to be coupled with 
basalt. 


Tue Law or RicutHoren.—While Bunsen’s remarkable law offered a 
thoroughly satisfactory chemical scheme, a sort of projection on which the 
chemical latitude and longitude of volcanic products might be laid down, 
as in any way affording a key to the natural succession of volcanic 
rock it was soon seen to be totally valueless. The frequent sequence of 
certain pyroxenic species after trachytic seemed at first to warrant the 
prevalent belief that the liquid interior, as deep as it was the source of 
ejected rocks, was arranged by its relative acidity in two zones of the nor- 
mal magmas of Bunsen, and that the lighter acidic magma, since from its 
lower specific gravity it must lie nearest the surface and hence be erupted 
first, would of necessity be followed by the deeper, heavier, pyroxenic 
material. But when the minute results of petrographers came to be carried 
into the field, it was found that the actual succession of volcanic products 
was excessively complicated, and that the simple and beautiful law of 
Bunsen gave no clew whatever to the causes or relations of the observed 
natural sequence. 

Petrographers most often contented themselves with a laboratory study 
of the mineral constitution of species, and while the science gained in com- 
plexity under their hands, it likewise equally fell into confusion from the 
geognostical point of view. 

In 1860 Richthofen* first announced his law of the Natural Succession 
of Volcanic Rocks, a statement more fully expressed and illustrated in his 
classic memoir on the “Principles of the Natural System of Volcanic 
Rocks.”’+ 

Richthofen’s scheme of ‘the succession of massive eruptions during 


* Jahrbuch der K. K. geologischen Reichsanstalt in Wien, Vol. XI. 
t Memoirs of the California Academy of Sciences. Vol. I. 1867. 


682 SYSTEMATIC GEOLOGY. 


the Tertiary and Post-Tertiary ages” is as follows, beginning with the most 
ancient group : 

. PROPYLITE 

. ANDESITE. 

TRACHYTE. 

. RHYOULITE. 

. BASALT. 


oe WW tk oe 


As already announced in the opening of this chapter, the great number 
of widely spread volcanic occurrences discovered and studied by this Ex- 
ploration offers but one obscure, questionable exception to this chemically 
singular sequence. I have also taken into this comparison the results of 
many thousands of miles of geological travel in other parts of the Cordil- 
leras, and in no case have I to report a valid exception to the law. 

Certainly it may be said with all safety that our ten years’ labor has 
resulted in the complete establishment of what can only be called the Law 
of Richthofen. 

This author, in his Classification of Voleanic Rocks, in the remarkable 
memoir already cited, divides the order andesite into, 1, hornblende- 
andesite, and 2, augite-andesite—separating the order propylite into, 1, 
quartziferous propylite or dacite; 2, hornblende-propylite; 8, augitic 
propylite. 

Since the date of his production it has been found that quartziferous 
eruptions were common to both the orders propylite and andesite, and that 
the two products, besides their time-separation, were microscopically dis- 
tinguishable by a variety of permanent characteristics, being the same 
points which clearly separated propylite from andesite, with the added 
difference that the quartzes of quartz-propylite carry fluid, while those of 
dacite or quartziferous andesite bear only glass inclusions; the main essen- 
tial difference being that the irregularly cleavable green hornblende made 
of staff-like microlites is common in and confined to the hornblendic and 
quartzose propylites, while the brown-black bordered hornblende is simi- 
larly confined to the andesites and dacites. For the other concurrent diag- 
nostic points of difference, the reader is referred to Zirkel’s memoir.* 

This separation has had the result of fixing dacite as the quartzifer 


* Geological Exploration of the Fortieth Parallel, Vol. VI., pages 133 and 141. 


CORRELATION OF VOLCANIC ROCKS. 683 


ous member of andesite, with which its time-relation also concurs, and places 
the proper quartziferous propylite as an acid member of the propylitic order. 

The list of voleanic rocks has been further amplified through the labors 
of our corps by the addition to the order of trachytes of a characteristic 
augite member. This rock, composed of sanidin and augite with inferior 
amounts of plagioclase and brown hornblende, is one of the family of Ter- 
tiary eruptions, and succeeds the main if not all sanidin-trachyte ejections. 

The law of Richthofen, as set forth by him, goes no farther than to 
assert the succession of the five orders as integers, not attempting to estab- 
lish within the limits of single orders what the sequence of their subdi- 
visions may be. 

Since no one could claim that rocks so different as sanidin-trachyte 
and augite-trachyte, or dacite and augite-andesite, could be the superficial 
and post-eruptive differentiation by crystallization from the same magma, in 
order to complete the detailed law of natural succession it is necessary not 
only to prove the place in the series of each of Richthofen’s orders as a 
whole, but to discover within each order the time-place of all the sub- 
divisions. 

Some progress toward this essential rounding out of the law has been 
made by this Exploration. 

As regards the rhyolites and basalts, they are at present considered by 
petrographers as separate and independent rocks, the former having no au- 
gitic representation, and the latter no acidic variety, the few quartziferous 
basalts containing the mineral as an accessory ingredient which never 
enters into the composition of the groundmass. 

The other three orders, however—propylite, andesite, and trachyte— 
all embrace quartziferous and augitiferous members besides the mean mem- 
ber, in which hornblende or biotite is rather abundantly present. 

In the case of the propylite order we have but one obscure, much 
decomposed occurrence of the augitic member, that of the Lower Truckee 
Canon, in which its relations to diorite, trachyte, rhyolite, and basalt are 
seen, but not to other propylitic forms. At Washoe quartzose and horn- 
blendic propylite are seen in conjunction, and there quartz-propylite was 
considered to be later, but as since the period of these observations quartz- 


684 SYSTEMATIC GEOLOGY. 


propylite and dacite have been separated, a doubt is thrown over the 
reading of that locality. . 

Otherwise the only contact between the two types was seen in Cortez 
Range, near Wagon Canon, where the relations again are obscure, but 
where the quartz-propylite seems to have been the later eruption. 

Within the order propylite, therefore, there is nothing fixed by our 
observations. 

Among the andesites our results are both positive and are multiplied 
by numerous contacts. 

First, as between andesites and propylites. At Washoe propylite is 
invaded and overlaid by both hornblende-andesite and dacite. ‘The Wagon 
Canon quartz-propylites are followed by both dacites and andesites. Berk- 
shire Canon propylites are earlier than andesites and dacites. There is no 
semblance of an exception to the law as between these two orders. 

Secondly, within the andesite order we have at Wagon Canon dacite 
cutting hornblende-andesite, and the same is true at Berkshire Canon. 

Wherever augite-andesite and hornblende-andesite are in contact, as at 
Jacob’s Promontory, Augusta Range, and Wagon Canon, the augitic rock 
is manifestly the later, and hence the latest of the three rocks. The 
sequence for the andesite order is therefore — 


1. Hornblende-andesite. 
2. Dacite. 
3. Augite-andesite. 


The general relations of priority established by Richthofen between 
trachytes and andesites hold uniformly good for the Fortieth Parallel 
area. 

At Washoe both types of trachyte are later than hornblende-andesite. 
On the Traverse Mountains, near the west base of the Wahsatch, are little 
outcrops of andesite overspread by sanidin-trachyte. So in Palisade Canon, 
at Crescent Peak in the Augusta Mountains, and in Virginia Range north 
of Truckee Canon, trachytes are seen distinctly overlying andesite, both 
hornblendic and augitie. The dacites of Mullen’s Gap and Berkshire are 
also capped by the heavy flow of sanidin-trachyte. 


CORRELATION OF VOLCANIC ROCKS. 685 


Within the trachyte order we have seen that there are three distinct 
types: 

1. A hornblende-plagioclase-trachyte, in which triclinic feldspar nearly 
and sometimes quite equals sanidin, and in which the union of plagioclase 
and hornblende produces a habitus approaching andesite. From that rock, 
however, the plagioclastic trachyte may be readily distinguished by the 
character of the groundmass, which is unmistakable. 

2. The regular sanidin-trachyte. 

3. Augite-trachyte. 

At Washoe and in Pinon Range, where the first two varieties are 
observed in contact, they are in the order mentioned, the plagioclase rock 
having a bedded and columnar structure. In volume it is evidently the 
least. 

A fourth variety of trachyte, characterized by the abundant presence 
of granules of free quartz, constitutes a member parallel to the dacites and 
quartz-propylites, with the exception that the quartz of the trachytes in no 
case enters the constitution of the groundmass, but is present in purely 
segregated granules, rarely or never dihexahedral, and never appearing of 
microscopic size. 

Besides the true augite-trachyte, very many exposures of the sanidin 
species contain accessory augite, either in the presence of biotite or asso- 
ciated with hornblende. This occurrence resembles the case of accessory 
augite in the true hornblende-andesites. There is never enough augite to 
produce the true pyroxenic habit. 

The quartziferous trachytes only occur in presence of the other varie- 
ties in Wah-Weah Range, where their relations of succession were not 
made out. 

The andesitoid-trachytes, characterized by the presence of plagioclase 
in proportion nearly equalling the orthoclase and sanidin, are invariably 
earlier than the true sanidin types. All the trachytic outbursts of the two 
eastern districts in the region of the Wahsatch and the Rocky Mountains 
are varieties with more or less free quartz and a large amount of accessory 
augite. They are comparatively uniform, and all the rocks of both of 
these large exposures represent the same general type. 


686 SYSTEMATIC GEOLOGY. 


True augite-trachytes occur only within Virginia Range, and there 
they are unmistakably later than the great outflows of sanidin-trachyte 
which crown the range north of Truckee Canon. Here, as in the case of 
the andesite order, the augite member is the latest. 

Between the trachyte and rhyolite orders the relations of succession 
are more difficult to make out. As a general rule, trachytic bodies are 
not seen in direct contact with the rhyolites. On the divide between 
North and Middle parks, in the Rocky Mountains, from the situation of the 
two outbursts it is evident that they do come in contact, but the region is 
obscured by an enormous amount of glacial débris and covered by a dense 
forest. In the region of Pinon and Cortez ranges, however, the two rocks 
are seen directly in contact, and in these cases the rhyolite is clearly 
superposed on the trachyte, having surrounded and nearly overflowed it 
The trachytic body at the northern end of Montezuma Range, near the 
northern margin of Map V., is another locality of contact in which the 
unmistakable signs are of the rhyolite having broken out later than the 
trachytes ; but the most characteristic locality of all is that of Virginia 
Range, directly north of Truckee Canon. There the broad field of sanidin- 
trachyte, which forms the mass of the range for fifteen or sixteen miles, is 
broken through by a powerful outburst of rhyolite, which has built a lofty 
series of conical and domed hills, culminating in Spanish Peak. 

Outside of the Fortieth Parallel area, on the great chain of axial vol- 
canos which rise at intervals along the crest of the Sierra Nevada and 
Cascade ranges, there are cases of the direct superposition of rhyolites over 
trachytes. An interesting instance is the most recent cone of Lassen’s 
Peak, which, as described in the Geological Survey of California, is built of 
late rhyolitic flows which have broken through a foundation-region of gray 
trachytes, they having come to the surface within the ancient crater-line 
of a former and far grander andesite volcano. In the interesting volcanic 
region of Mono Lake, where there is a superb display of volcanic glasses, 
pearlites, and acidic pumices, the entire rhyolite field has sueceeded normal 
sanidin-trachyte. Considering, however, the frequency of trachytes and 
rhyolites, it is not a little noticeable that they usually occupy quite inde- 


pendent regions, and the instances of contact or superposition are more 


CORRELATION OF VOLCANIC ROCKS. 687 


rare than between any two of the other volcano orders. We have seen that 
through the three earlier orders each one was characterized by an augite 
member. ‘The present definition of rhyolite admits no pyroxenic form; 
but, for reasons to be adduced in the succeeding section, I have come to 
consider basalt as the augite-correlative of rhyolite; and in the multitude 
of instances where these two rocks are found in contact, basalt is invariably 
the more recent, with the single exception, already noted, at Black Rock, 
where there are structural difficulties, and where there appears to be one 
of those interpolations of successive flows of basalt and rhyolite such as 
are described by Hochstetter in the voleanic field of New Zealand. Richt- 
hofen, in his memoir on the Natural System of Volcanic Rocks, calls at- 
tention to the infrequency of contact-relations between rhyolite and basalt. 
This rule, which he has drawn from his wide personal examination of vol- 
canic fields, does not hold good in the Fortieth Parallel area. As will be 
seen by a glance at the Map accompanying this chapter, the contact of the 
two is not uncommon, and there can be no mistaking the fact that their 
relations are as stated. In the Rocky Mountain field, basalts directly 
overlie the trachytes, but the single rhyolitic region lying along the west 
base of Medicine Pole Range has within our field no basaltic connec- 
tions. The prominent rhyolitic region of the Fortieth Parallel is west 
of Salt Lake Desert. From the 114th meridian to the 120th no single 
range is free from rhyolitic outflows, and in a majority of cases more or 
less basalt is found in contact with it. The northern end of Ombe Range 
is an interesting example of the overlie of basalts. Here, as already 
described, a thick sheet-flow of black basalt directly caps the round rhyo- 
litic hills. The curious group of white rhyolitic breccias of the Beehives 
in the Ruby group furnishes an interesting example of the relation of these 
two rocks. There the thin black basalts are seen in irregular masses, the 
relics of erosion, lying upon the summit of the white breccias. Pinon 
Range furnishes two examples of the overlie of basalt, one on the east 
base of the range near the gateway of Pinon Pass, and the other in the 
angle of junction between Palisade Canon and the Eureka Railroad. In 
Cortez Range the lofty mass of rhyolite which overflows the quartz- 
propylites between Cortez and Papoose peaks is overlaid on the eastern 


688 SYSTEMATIC GEOLOGY. 


foothills by a general sheet of basalt which overwhelms and margins 
all the earlier voleanic species. One of the most extensive and inter- 
esting cases of overflow by basalt is that of the Shoshone Mesa 
This singular plateau rises from the level Quaternary plains of Hum- 
boldt Valley and Rye Meadows, showing an abrupt escarpment of about 
2,000 feet. The lower half of this great, sharp wall of voleanic rock is 
composed of rhyolite, and the upper half of remarkably bedded black 
basalts. The Augusta Mountains—the greatest single body of rhyo- 
lites in the whole Fortieth Parallel area—are broken through at various 
points south of Shoshone Cafon, and near the northern extremity of the 
group, by dikes of basalt which have piled up their limited outflows on the 
tops of the great rhyolitic mountains. White rhyolitic cones near the 
northern end of the range—the only true volcanos within our field of 
exploration—not only are succeeded by black basalts, but the latter rocks 
have distinctly come to the surface through the old rhyolitic craters, and 
overpouring the rim, or breaking through breaches in the crater walls, have 
flowed out in distinct lava streams down the exterior slopes of the rhyo- 
litic cones. No more evident and unmistakable exhibitions of basaltic 
sequence may be seen than in the Sou Spring Hills, where a rugged group 
of rhyolitic mountains has been broken through by a series of black basaltic 
dikes, whose overflow spread out in thin sheets over the more level por- 
tions of the rhyolitic summits. Table Mountain, in Pah-Ute Range, is a 
similar case where a thickness of two or three thousand feet of basalt 
has been superposed on an already extensive accumulation of rhyolites. 
‘qually unmistakable is the relation in Montezuma Range, the south- 
ern half of that complicated structure being for the most part formed of 
four or five successive outflows of rhyolites. Through these extensive 
rhyolitic bodies have broken a great number of basaltic dikes, which have 
poured out in important fields covering fully a quarter of the underlying 
rhyolite. Spanish Peak, north of Truckee Canon, is three quarters sur- 
rounded by more recent flows of basalt, which have piled themselves up 
unconformably against the rhyolitic slopes, leaving only the central mass 
lifted above the basalt. Near the mouth of Antone’s Canon the pure white 


felsitic rhyolite—a depeudent flow of the Spanish Peak mass—is capped 


CORRELATION OF VOLCANIC ROCKS. 689 


by an extremely fine-grained, jet-black, lustrous basalt, whose liquid flow 
occupied all the hollows and ravines of the rhyolitic topography. 

Professor Whitney has shown, in the Geology of California, the sequence 
of basalts after rhyolites at Lassen’s Peak; and in studying the structure of 
the great cone of Shasta, it was there seen that north of the mountain is a 
series of true rhyolitic cones subsequent to the great trachytic peak itself. 
Iu the surrounding foot-hills of Mount Shasta is a series of interesting 
basaltic eruptions, which have come to the surface through the lower por- 
tions of the trachyte slopes. These fissures have given vent to important 
streams of basalt, which have flowed down prior valleys of erosion, and in 
their northward extension have surrounded and overwhelmed the base of 
the rhyolitic cones. 

In western Arizona, and in the Great Colorado Desert of southern 
California, I have observed at several localities the same superposition of 
basalt over rhyolite. There can be no manner of doubt that both the 
enormous numbers of massive eruptions of these rocks and the actual 
voleanic cones of the Sierra Nevada and Cascade ranges fall distinctly 
and uniformly within the law of Richthofen. 

On grounds which will be explained in the following section, I have 
concluded to consider basalt as the augite-correlative of rhyolite, and, 
since the combination of those two orders of Richthofen into one new 
order is upon my own responsibility, I have concluded to bestow upon 
the united order a name, and in view of the relative newness of its 
ejecta propose for it ‘“Neolite,” in which rhyolite and basalt represent 
the acidic and basic members, exactly as within the orders trachy tes, 
andesites, and propylites Richthofen has assembled the different chemical 
expressions in one natural group. While, therefore, considering the 
volcanic products simply in the light of natural groups, or, as Richthofen 
has called them, orders, his law of succession has seemed to hold uniformly 
good, it is the attempt of the present section to carry that law of succession 
into greater detail and to make out a full scheme for the periodic succession 
not only of the orders but of the subdivisions within the orders. It has 
already been said that the succession of three subdivisions of propylite is not 
clearly made out by us, but within the orders andesite, trachyte, and neo- 

44 Kk 


690 SYSTEMATIC GEOLOGY. 


lite it has been clearly seen that the acidic members are in each order 
invariably followed by the pyroxenic members. The quartziferous mem- 
bers are also, for andesite and trachyte, held to be intermediate in time 
between the hornblende-mica member and the augite member. Since this 
holds good in the groups where we have been able to establish the relation, 
the probability is, that propylites also fall into the same sequence, and that 
augite-propylite closes the eruptions of that natural group. Provided 
they do—which yet remains to be proved—there will be the following 
sequence : 


NATURAL SUCCESSION OF VOLCANIC ROCKS. 


ORDER, SUBDIVISION. 


1, PROPYLITE....a. Hornblende-propylite. 
b. Quartz-propylite. 
c. Augite-propylite. 
TAN DESIDEE--.4- a. Hornblende-andesite. 
b. Quartz-andesite (Dacite). 
ce, Augite-andesite. 
TRACHYTE ....a. Hornblende-plagioclase-trachyte. 
. Sanidin-trachyte (quartziferous). 
. Augite-trachyte. 
. Rhyolite. 
. Basalt. 


bo 


oo 


4, NEOLITE....- 


ca oe 


If Iam able later to show good reason for uniting such chemically op- 
posing types as rhyolite and basalt under one natural order, I trust that the 
eminent founder of the law of natural periodic succession of volcanic rocks 
will accept neolite and the slight modification of his statement, and still per- 
mit his name to be connected with the law which I have done nothing to 
invalidate, having sought only to amplify it and apply it to the minuter 
subdivisions. 

Comparing the law of sequence with the quantitative products of 
eruption, it will be seen that, when compared as orders, the quantities are 
inversely as the antiquity, the earliest orders having produced the smallest 
amount of ejecta. Within each separate order the quantitative relations re- 
verse this law, and the acidic member of each order has produced far greater 
outflow than the latest augite member. I do not attempt to carry this com- 


CORRELATION OF VOLCANIC ROCKS. 691 


parison between age and volume beyond the limits of the western United 
States, where, in spite of the enormous superficial development of basalt, 
I believe that the relation will hold firm. 

It is unnecessary to repeat here the diagnostic points upon which either 
the orders or the submembers of the orders are to be distinguished from 
one another. I only wish to emphasize the fact, first, that each order, being 
& time group, has impressed upon it certain petrographical features which 
are uniform through all the subdivisions; secondly, that within any single 
order the subdivisions bear to each other a relation harmonious with the law 
of Bunsen, each order containing an expression of a mean chemical product 
and of the normal trachytic and pyroxenic magmas; although in the case of 
the earlier orders the extreme members of the pyroxenic type are less basic 
than those of the neolite order, and consequently do not reach the last and 
most basic term of Bunsen’s series. 

In the more general relations of the volcanic group, decidedly the most 
interesting question concerns the relations of its members to the continuous 
geological history of the period in which they have made their appearance. 
Unfortunately, as in the purely petrographical domain, the paucity of ex- 
posures of the propylite group defeats an exact fixing of their geological 
date. The internal evidence of supposed Tertiary leaves, which are found 
in abundance in the propylitic tuffs, weighs but little. The sole indication 
of their time-relations is to be found in the obscure mass lying between 
Montezuma and Truckee ranges, and where the stratified Miocene deposits 
surround an early propylite eruption, with every appearance of being later 
and unconformable. _Propylites are, therefore, probably pre-Miocene, and 
are likely eventually to be dated somewhere within the lapse of Eocene 
time. The latest stratified rocks anterior to them in age in the country of 
their exposure are the upper Jurassic slates, and the total area in which they 
have been erupted did not again become a region of sedimentation until the 
dawn of the Miocene. There are, therefore, no data for conclusively fixing 
the exact age of propylites. 

Of the hornblende-andesites little more may be said. They, too, are 
distinctively earlier than the Miocene strata, as may be seen in the low lands 


between the Kamma, Pah-tson, and Montezuma mountains, where the in- 


G92 SYSTEMATIC GEOLOGY. 


clined Miocenes abut directly against eroded slopes of andesitic mountains. 
But it should be repeated here that these andesites are of the hornblendic 
variety, and that in the lowest of the Miocene series are found palagonitic 
tuffs whose chemical nature has led me to correlate them with the andesites 
and to consider them as simply the sedimented tuffs of the augite-andesite 
period. If this correlation is correct—and it coincides with all the facts 
we now have—the beginning of Miocene time would have come between 
the main period of hornblende-andesites and that of augite-andesites, which 
would have the effect of placing dacites, hornblende-andesites, and all the 
propylites in Eocene time. In the case of the trachytes the evidence is far 
clearer. A very large portion of the enormous bulk of fresh-water beds 
of the Pah-Ute Miocene lake are really trachytic tuffs, which in Oregon 
show a thickness of 4,000 feet, and in Nevada certainly 2,500 feet. 

In the former locality these trachytic tuffs are literally crowded with a 
typical Miocene fauna already catalogued in the Cenozoic chapter. No 
characteristic fossils have been found in the lowest beds of the tuff series in 
the horizon of the palagonite tuffs, and it is not impossible that when found 
they may carry back even the augite-andesite period within the Eocene; but 
the whole thickness of trachytic tuffs from bottom to top is unmistakably of 
Miocene age. This great series of volcanic lake deposits subsequent to the 
Kocene has its beginning at the close of a period of enormous erosion. 

The Eocene, as a whole, was remarkable over the Fortieth Parallel area 
for the intensity, rapidity, and grandeur of its processes of disintegration and 
removal. Like the deposits of the Alps and the enormous Locene fields of 
Asia, it stands out in-the Tertiary as a great interval of degradation and 
sedimentation. The four periods of orographical activity already demon- 
strated by the change of boundary and sediments of the four Eocene lakes, 
would afford ample disturbance-for the ejection of the various members of 
propylite and andesite families which came to the surface before the Mio- 
cene trachytic age. 

The more important Fortieth Parallel trachytic eruptions are those 
which lie at the east and west boundaries of the basin of the Colorado upon 
lines of weakness which were developed at the close of the Cretaceous, and 
which were again regions of disturbance during and at the close of the 


CORRELATION OF VOLCANIC ROCKS. 693 


Eocene period. The next most important trachytic outflows are those 
within the limits and along the borders of the old Pah-Ute Miocene lake. 
During the Eocene we have no evidence that the latter area was occupied 
by water; on the contrary, all the known facts tend to the belief that it 
was a land region, and that at the dawn of the Miocene or in the latest 
of the Eocene time it was suddenly depressed to form a great lacustrine 
basin. It was the fissures incident to this great subsidence that gave vent 
to the trachytes whose eruptions along the lake-borders built them- 
selves up as mountain masses and cones, while the enormous subaqueous 
ejections were rearranged as the Miocene tufts. 

The close of the Miocene and the close of the trachyte period coincided, 
and at this epoch a very severe dynamic disturbance took place; all the 
beds of the Miocene lake were thrown into folds, and erosion at once began 
upon the highest exposures of the Miocene folds. 

The lines of trachytic eruption as developed on the Fortieth Parallel 
are in general northwest-southeast lines. The northern part of Virginia 
Range shows an extension of trachytes parallel to the trend of the Sierra 
Nevada. The Wahsatch group has its chief line in the northwest-south- 
east strike, with a subordinate series of contemporaneous eruptions 
trained at right angles to this line. The Rocky Mountain group consists 
of two masses, of which one is northwest of the other. The Wahsatch 
and Rocky Mountain trachytes have broken out along the flanks of the 
previous lofty ranges, not in either case invading the summit region. 
In the case of Virginia Range the trachytes are north of the high ancient 
group of mountains which had its culmination in the region of Washoe. 
The trachytes here were high mountain eruptions, and piled up their ejecta 
over the depressed summit of the range. 

The great and elevated region of the Sierra Nevada from the latitude 
of the 40th parallel south is comparatively free from trachytes. They 
make their great development in the northern or depressed part of the 
range and the low ridge of the Cascade, upon which they have built lofty 
isolated cones. 

Either accompanying the folding of the Miocene beds or not long 
subsequent, through a new series of fissures, the rhyolites broke out. 


694 SYSTEMATIC GEOLOGY. 


The greatest rhyolitic line is that of the broad group of ranges in middle 
Nevada, which is a northeast-southwest line, or approximately at right 
angles to the Sierra. . 

The region over which the great rhyolitic eruptions have taken place 
within the I*ortieth Parallel area was a country of great mountain folds 
that had existed since the close of Jurassic time. In the series of disturb- 
ances which closed the Miocene and compressed the trachytie  tuffs 
and their accompanying sediments into waves, the folds of the Jurassic 
ranges were dislocated by a series of approximately vertical faults, accom: 
panied by a remarkably varied displacement. Single ranges were divided 
into three or four blocks, of which some sank thousands of feet below the 
level of others. The greatest rhyolitic eruptions accompanied these loci 
of subsidence. Where a great mountain block has been detached from 
its direct connections and dropped below the surrounding levels, there 
the rhyolites have overflowed it and built up great accumulations of ejecta. 
Wherever the rhyolites, on the other hand, accompany the relatively 
elevated mountain blocks, they are present merely as bordering bands 
skirting the foot-hills of the mountain mass. There are a few instances 
in which hill masses were riven by dikes from which there was a 
limited outflow over the high summits; but the general law was, that 
the great ejections took place in subsided regions. Quantitatively, these 
rhyolitic ejections were of enormous volume, building up mountain 
groups 38,000 to 6,000 feet in thickness, in blocks seventy or eighty 
miles in length. Where seen in contact with the Miocene it has broken 
through the disturbed and faulted strata and overflowed a topography 
which was the result of erosion of the Miocene beds. In eastern Nevada, 
in the plateau region between the basin of Utah and that of Nevada, a 
considerable development of rhyolitie tuffs is found in an approximately 
undisturbed position. Eight hundred or a thousand feet of these are seen, 
consisting of fine glassy rapilli and sands, in which is entombed the char- 
acteristic fauna of the Niobrara Pliocene. It is interesting to observe that 
in the abundant rhyolite field of western Nevada the rhyolitic tufts are 
rare, never appearing in distinct lacustrine strata; on the contrary, all 


the rhyolitic eruptions which are seen in contact with the disturbed Mio- 


CORRELATION OF VOLCANIC ROCKS. 695 


cene beds are subaerial ejections of stony and glassy rocks, which is 
evidence that the first Pliocene lake in which the rhyolitic tuffs were 
deposited was an eastern Nevada lake, and that in early Pliocene times 
the area of the Miocene lake was dry land. The main great rhyolitic 
eruptions were all subaerial and to the west of the earliest Pliocene lake. 
In the section devoted to Tertiary lakes, I have shown that after the final 
deposition of the rhyolitic tuffs came an orographical disturbance, the 
nature and extent of which are unknown, which gave vent to basaltic 
eruptions. In the basin of Idaho sheets of the basaltic flows overlie 
horizontal undisturbed Pliocene beds of purely detrital origin. The sub- 
basaltic beds, from their fossils and their position, are held to be the equiv- 
alents in age of the undisturbed rhyolitic Pliocene tuffs, and to be the 
representative of the Niobrara portion of the whole Pliocene age. Subse- 
quent to the first basaltic appearance there were no rhyolites; they were, 
therefore, wholly post-Miocene, and confined to the lower division of the 
Pliocene, equivalent to the Niobrara beds of the Great Plains. The geo- 
logical relations of the basaltic outflows are highly varied. They appear 
as the trivial outpourings of dikes in the hearts of many of the mountain 
ranges, but their great réle throughout the West is that of broad sheets 
occupying comparatively level areas, having overflowed the surfaces of 
plateaus or spread themselves in repeated conformable sheets over wide 
valleys. In the Fortieth Parallel region, subsequent to the last basaltic 
activity, a second series of Pliocene deposits has been laid down, covering 
a large amount of the basaltic field Fossils in this post-basaltie Miocene 
are extremely rare, and their facies very recent. It is highly probable that 
since the entire cessation of the great basaltic eruptions a lingering activity 
has been maintained at a few widely separated localities, particularly in the 
Sierra Nevada. 


NEC LTON Vil: 


FUSION, GENESIS, AND CLASSIFICATION OF VOLCANIC ROCKS. 


Fusion.—Starting from the one central fact of the enormous extravasa- 
tion of molten rock material which has been recognized by geologists both 
in the act of ejection and as the superficial product of eruptions in past 
time, all questions concerning the general subject of vulcanicity resolve 
themselves into the one preceding problem of the origin of fusion. Three 
distinct theories have been thus far advanced to account for hypogeal heat: 

First, the chemical doctrine of Davy, that deep within the material of 
the globe there exist chemically active elements which are and have been 
in the act of energetic combination, disengaging heat. This idea, finally 
abandoned by Davy himself, was so totally opposed to all known facts 
relating to the materials of the earth as to have completely failed to gain 
any respectable following. 

Secondly, the old Plutonic idea, of a molten globe enveloped by a thin 
congealed crust, since its early advocacy, has always found an abundant 
company of geological believers. Even to-day, in spite of physical and 
astronomical arguments to the contrary, a respectable body of geologists 
finds no solution of the facts of voleanic geology save in the assumption of 
a general liquid interior, owing its mobility to igneous fusion. According 
to their belief, the earth is still in its early stages of cooling, and the great 
globe of molten matter is but little advanced from its first concentration 
into a revolving sphere under the conditions of the nebular hypothesis. 
Insuperable objections have been advanced against this doctrine by Wil- 
liam Hopkins, in his ‘Researches in Physical Geography,” 1839.* The 
conclusion of Hopkins that the earth has the rigidity of a solid globe, 
and therefore cannot be in the main liquid, was later substantiated by the 
researches of Sir William Thomson on the Rigidity of the Earth,t in 


696 *Philosophical Transactions for 1842. Part II. 
t Philosophical Transactions for May, 1862. 


VOLCANIC FUSION. 697 


which he concludes that the earth must have the rigidity of steel or glass. 
A reéxamination of these views, in which he abandons the Hopkins argu- 
ment from precession, but holds to the argument from the tides, and rests 
in the conclusion of the great rigidity of the earth, is to be found in his 
address, as president of the Section of Mathematics and Physics, before 
the British Association for the Advancement of Science, at Glasgow, in the 
Report for 1876. Admitting, as we cannot fail to do, the validity of the 
physical arguments against a fluid interior, geologists are driven from that 
long cherished source, not only for the molten material of volcanic erup- 
tions, but for a general theatre of the ‘reactions of the interior against 
the exterior” crust upon which have been based all the theories of up- 
heayval and subsidence that have gained even temporary credence. 
Hopkins, in his considerations of the mode of cooling of the once 
molten globe, gives his belief to a theory of refrigeration, of which the 
following are the leading outlines: Owing to the enormous pressure at 
the centre and throughout the deeper portions of the molten globe, solidi- 
fication took place, first, by the raising of the temperature of fusion 
above the temperature of the mass; secondly, the formation, by congeal- 
ment, of a superficial cold crust, leaving between this rigid envelope and 
the solid middle a shell of unknown thickness of residual molten matter, 
which, in the accident of cooling, separated itself into detached lakes. It 
has been admitted that these residual lakes, if small enough, would not 
affect the physical conclusion of the general rigidity of the earth; but 
among geologists the phenomena of the igneous rocks, their chemical 
and mineralogical differences, and the secular petrological change which 
has been noted between the earliest and latest products of eruption have 
been held to render entirely improbable the existence of such permanent 
residual lakes. Hopkins’s argument in favor of these lakes rests, first, 
on his ideas of the sequence of events in cooling, and their continuous 
existence in a state of fluidity is only explained by him under the notion 
that they are composed of matter more fusible than the surrounding and 
bounding regions of the solid earth. Robert Mallett, in his paper on 
“Volcanic Energy,”* very justly remarks, as an objection to this notion, 


*Philosophical Transactions. Volume 163. Part I. 1873. 


698 SYSTEMATIC GEOLOGY. 


that there is absolutely nothing in our knowledge of the earth’s crust to 
warrant a supposition of isolated masses of greater relative fusibility. The 
most important geological objection to permanent residual lakes is the vary- 
ing character of volcanic products erupted in the same region. Another 
geological objection to supposing the residual lakes to be connected in a 
continuous shell of molten matter, is the total want of sympathy in vol- 
canic action between closely contiguous vents, and the well known fact 
that adjacent volcanos simultaneously pour out materials of widely differ- 
ent chemical and mineralogical character. Similar objections might be 
made from the geological point of view to a generally fused interior. 

The third conception by which to account for fusion is Mallett’s 
own. His theory is the production by mechanical means of local lakes 
of fusion within the solid matter of the globe by the crushing of the earth’s 
solid crust from the terrestrial contraction due to secular refrigeration. 
Assuming the earth to be still a very hot body, from the observed increment 
of temperature in depth, and that the materials of the earth are such as 
contract by the loss of heat, he reasons that the exterior remains at a 
temperature rendered stable by radiation into space, while the nucleus, con- 
stantly losing volume by the outward conduction of its heat, tends to 
shrink away from the crust, leaving the latter partially unsupported; that 
by the continual shrinking away of the contracting nucleus a shell of weak 
support is formed, and the unsupported crust eventually falls by its own 
gravity; that the work expended in the process of crushing the rock at the 
surfaces of impact is transformed into heat; that this heat raises the crushed 
material to the point of fusion. Physical objections have been raised to 
this by the Rev. O. Fisher, by C. E. Dutton,* and by Pfaff-+ 

The conception of Mallett seems to be based upon an assumption of 
sufficient rigidity of crust to sustain itself on the principle of the arch while 
the contracting nucleus shrinks away, leaving either vacuity or a shell of 
relatively slight density. This idea, which might easily be true of a very 
small sphere either of homogeneous material or of matter arranged in 


shells which increase in density toward the centre, seems totally inappli- 


* Penn Monthly, May, 1876. 
t Allgemeine Geologie als exacte Wissenschaft. 


VOLCANIC FUSION. 699 


cable when applied to a globe of the size of the earth. One of the most 
noticeable features in the rocky material of the crust, as observed by 
geologists, is the extraordinary plasticity of the most apparently rigid 
materials. The flexing and crowding together of rigid quartzitic strata, the 
remarkable plasticity of granite rocks as shown in the torsion of mountain 
ranges, the plasticity of a rock so highly crystalline as marble, tend together 
to show that the earth’s materials, as we know them, must in a large way be 
considered as distinctly plastic. If the materials of the superficial crust are 
so plastic as to be folded, flexed, and deformed by tangential pressure, it is 
impossible to suppose them sufficiently rigid to sustain themselves on a 
large scale on the principle of an arch, while actual vacuity was developed 
beneath them by the shrinking of the nucleus. It is vital to Mallett’s 
theory that this vacuity should be formed, and its formation is entirely at 
variance with the observed plasticity of the rocky material. If granite and 
marble are able to yield without fracture to a shearing stress, it is incon- 
ceivable that materials at all resembling them should sustain themselves in 
a thin spherical shell. 

That the operation, according to Mallett’s theory, must be extremely 
superficial, is evident from the character of the products of fusion, since all 
the extravasated rock falls within a range between a specific gravity of 2.5 
and 3.1. It obviously could not have been formed where the average 
density of the crust was greater than the higher figure. The very nature 
of voleanic rocks necessitates their having been formed within superficial 
shells of low specific gravities. Mallett’s self-sustaining shell must, there- 
fore, be so thin as to lie wholly above a depth represented by a shell of 
the maximum specific gravity of ejected material. When we realize that 
the mean density of the earth is attained at less than 1,000 miles in depth, 
and that the heaviest known lavas do not exceed 38.1, it is clear that the 
self-sustaining shell of Mallett must be excessively thin. A further evi- 
dence of this necessity is in the probable shallowness of the theatre of 
voleanic activity as demonstrated by the focal point of earthquake waves 
accompanying eruption. To suppose a self-sustainingly rigid shell of only 
fifty or sixty miles in depth, made of the yielding materials of the known 


crust, is to suppose a physical impossibility. Everything we know of the 


700 SYSTEMATIC GEOLOGY. 


physical properties of the superficial rocks leads us to believe that the 
formation of vacuity by the settling away of the nucleus would be utterly 
impossible; every property of rocks indicates that the crust would follow 
down the shrinking nucleus, change its molecular arrangement, and yield 
to the necessary tangential strain by the readjustment of its chemical com- 
binations. 

The series of experiments upon which Mallett bases his results was 
the crushing of cubes of rocky material under conditions in which the 
amount of work expended could be accurately estimated. His cubes were 
placed upon a bed and crushed by a descending plunger, but they were 
totally unsupported upon the four sides. The first effect of the increased 
pressure was an appreciable diminution of the height of the cube, the 
second effect a series of vertical cracks, which may be otherwise expressed 
as a lateral increase of dimensions of the cube. Now, unless the supposed 
vacuity is really formed within the solid shells of the crust, the crushing 
conditions do not fairly represent the operations of nature. If there is 
absolute continuity of material without vacuity throughout the whole 
radius of the earth, then the effect of downward pressure involves not the 
simple behavior of the cube of rock able to spread in all directions later- 
ally, but the relations of a particle under far more complicated dynam- 
ical conditions. It is obviously incorrect to compare the evidences of the 
superficial applications of geological pressure with those at the depths of 
the loci of volcanic fusion, but all we know of the crushing effect of tan- 
gential strain or vertical pressure developed or shown on the surface of the 
globe is not at all in the direction of crushing. When thousands of feet 
of the rocky superficial matter of the globe are thrown into waves and 
folds and enormously compressed, the effect is to obliterate the form of the 
original particles out of which the rock was built up, and to produce new 
molecular combinations. When from the depth of 50,000 or 60,000 feet 
a break in the crust brings to the surface underlying sedimentary beds, 
as in the case of the Cambrian or Archeean strata, the effect upon the orig- 
inal sedimentary particles has not been to crush them, but rather to weld 
them. Between the deep and the shallow strata there is a constant percepti- 
ble change in the direction of consolidation, not of crushing. It is true that 


VOLCANIC FUSION. 701 


the tangential work which has been employed on the surface of the globe 
in the formation of mountain ranges may be quantitatively far less than the 
work used up in rock-crushing in depth under the supposition of Mallett; 
but without vacuity it is difficult to conceive of any separation of particles, 
which is the essential feature of crushing. In general, Mallett’s theory may 
be said to rest upon the formation of vacuity, which could only be formed 
under a superficial shell of far greater rigidity than that of the earth, and 
hence to be inadequate to explain those fused regions whose existence is 
definitely proven by the phenomena of molten lava. 

The greatest single difficulty which the whole theory of fusion has to 
contend with, is the extremely localized character of its phenomena, the 
fact of the non-sympathy of adjacent volcanic regions, and the chemical 
diversities of successive and contemporaneous products. 

If the generally molten interior is banished from consideration by the 
unanswerable objections of physical astronomers, and if the secular phe- 
nomena of volcanic geology seem to disprove the theory of the numerous 
residual lakes of Hopkins, and if the non-rigidity of the crust and its prob- 
able inability to sustain itself upon the principle of the arch are, as I 
believe, fatal to the theory of Mallett, what possible cause can there be to 
account for those extremely localized and only temporarily existing pools 
of fusion within the earth’s superficial shell which the facts of volcanic 
geology demand? The considerations which are about to be put forth 
here are little more than an hypothesis, which, at the present stage of his 
studies, is all the writer has to offer. 

It is first assumed that the earth is still, as Sir William Thomson 
holds, a very hot body in a comparatively early stage of refrigeration. 
Whether we arrive at the heat gradient of the earth’s interior by the pro- 
cess of reasoning employed by Thomson, in his paper on the secular 
refrigeration of the earth, or from an empirical formula derived from an 
accommodation of the conflicting observations of the actual augmentation 
of temperature in depth, the nature of that gradient in the superficial part 
of the globe is due in the main obviously to the law that conductivity is in 
the inverse ratio of temperature; and whether the interior is solid or liquid, 
from the nature of the rapid conduction through the congealed exterior shell 


702 SYSTEMATIC GEOLOGY. 


of the earth, the gradient must show a rapid increase of ordinates from 
the surface downward for a certain distance, and then a very slight increase 
of ordinates to the centre. In other words, the curve showing the rate of 
augmentation of the temperature downward will after a comparatively 
short distance show but slight change in its ordinates. A rapid change of 
temperature between different contiguous shells is confined to the superficial 
part of the globe. 

On the other hand, the pressure gradient, owing to the curve of density, 
will show its least rate of augmentation near the surface, where the densities 
are the least, and its greatest rate of augmentation in depth. From the 
relation of these gradients of heat and pressure it is evident that after the 
maximum curvature of the heat-gradient is passed, as it inevitably must be 
in the upper regions of the crust, since the pressure-gradient continues to 
show a constant increment of ordinates, the effect of pressure in raising the 
fusing-point must constantly increase below the maximum point of curva- 
ture of the heat-gradient; and from the slight increment of heat from that 
point down to the centre there will be a constantly greater effect of press- 
ure in raising the fusing-point. Whence it follows that the region where 
pressure has the Jeast effect in raising the temperature of fusion will be at 
or above the region of sharp curvature of the heat-gradient. In other 
words, in passing down from the surface of the earth, the temperature 
rapidly increasing, a point will be reached in the superficial crust of the 
earth where the effect of pressure in preventing fusion will be at its mini- 
mum; and below that point the increasing rate of augmentation of press- 
ure will render fusion more and more impossible down to the centre of 
the earth. 

Provided, as there seems no valid reason to doubt, the mean augmenta- 
tion of temperature were to continue approximately according to the rate 
shown by the empirical formula derived from observation, a shell would be 
reached at a depth of not over fifty miles in which the temperature of 
fusion would exist, but where fusion might be restrained by the downward 
pressure cf superincumbent material. If by any means a portion of the 
superincumbent weight should be suddenly removed, it is clear that a cer- 
tain liquid shell would form. Hopkins in his investigations actually sup- 


VOLCANIC FUSION. 703 


poses the existence of regions retained in fusion by the removal of superin- 
cumbent pressure by the formation of rigid arches. Another method of 
the reduction of pressure has occurred to the writer. 

Babbage and Herschel sought to account for several of the more diffi- 
cult problems of dynamic geology by the transportation of material on the 
surface of the earth by erosion and sedimentation, but their application 
was totally different from that which I am about to suggest. 

Starting with the well known fact that in general the isothermal couches 
must, from the law of conductivity, follow the superficial contours of the 
globe, and that the isobaric couches must also follow this configuration, it is 
evident that not far beneath the surface—probably within forty miles—there 
is a couche above the temperature of fusion, but restrained from fusion by 
pressure. Under continents that couche must rise, and under the deep basins 
of the ocean it must be depressed nearer the centre, following the superficial 
contours. According to that view, under each continent, and especially 
under each lofty mountain region, this shell of the temperature of fusion must 
rise to its maximum radial distance from the centre of the earth. This thermal 
topography will, therefore, have its peaks under the centres of high moun- 
tain systems. As is obvious from all geological study, high mountain 
ranges are the centres of the most active and intense erosion. Maximum 
removal, therefore, will actually take place over the immediate top of the 
peaks of the thermal topography, and there the column of superincumbent 
matter, or, as otherwise expressible, the actual superincumbent pressure, will 
be most suddenly and most remarkably varied during the history of erosion. 

Starting with a high mountain range, with its corresponding peak of 
thermal topography beneath it, and a surface-depression upon either side into 
the basins of the oceans, with a corresponding depression of the couche of 
fusion-temperature, what would be the effect when erosion begins? Suppose 
the material to be rapidly removed from the high mountain peak and trans- 
ported to and laid down in the ocean valleys. The effect is to remove the 
pressure from the mountain peak and add to it in the ocean bed. It is demon- 
strable, according to the views of Herschel and Babbage, that in the region 
from which material is taken, and whose downward pressure is thus lightened, 


the couches of temperature will sink correspondingly, and that over the 


704 SYSTEMATIC GEOLOGY. 


ocean region where the radii are loaded with more material the couches of 
temperature will rise. The immediate effect upon the couche of fusion- 
temperature will therefore depend on a question of rate. Let us examine 
the case of the mountain peak. Suppose above the temperature of fusion 
is a column of thirty miles of rock, and suppose three miles are rapidly 
removed by erosion. The position of the couche of the temperature of 
fusion will constantly tend to retire toward the centre of the earth. If it 
retires at the same rate as erosion, the effect of pressure on the couche of the 
temperature of fusion will remain the same; but if the rate of erosion and 
consequent removal of pressure is greater than that of the recession of the 
couche of temperature, plus that of general secular recession, the effect, it 
would seem, must be to create a local fusion. Professor James Thomson’s 
formula for determining the amount to which the freezing-point of water is 
lowered by known pressure might be quantitatively applicable to determin- 
ing the effect that the diminution of pressure by erosion would have in 
lowering the fusion-point of rock, if we knew the latent heat of fusion of 
the volcanic rocks, which, so far as I know, has not been determined, and 
the difference of specific gravity between the liquid and the solid state, 
of which existing data are quantitatively conflicting. Of course, obvi- 
ously, for the production of fusion by erosion it is essential that the rate 
of removal shall be greater than the recession of isothermal couches due to 
removal. a 

From the point of view of the Uniformitarian school, erosion sufli- 
ciently rapid to produce such results is inconceivable; but when we come 
to compare in western America the periodic eruptions of volcanic matters 
through the Tertiary age, it is seen that each new order of eruptions suc- 
ceeds a period of rapid erosion. It is clear, both physically and geologically, 
that the peaks in the couches of temperature will underlie the erosion centres 
of the globe, and it seems not improbable that the rate of removal exceeds 
the immensely slow rate of real thermal conductivity, and that the isolated 
lakes of fused matter which seem to be necessary to fulfil the known 
geological conditions may be the direct result of erosion. 

In this view, all continents which are the areas of erosion would, when- 
ever the removal of material exceeds the rate of recession of temperature, be 


GENESIS OF VOLCANIO SPECIES. 705 


underlaid by a bed of molten material, which would in general follow the 
contour of the surface, but which would be thickest under places of most 
rapid and excessive erosion. 

The anomalies of the earth’s gravity, as shown by pendulum experi- 
ments, has led to a general law that the gravity upon continents is less 
than that upon islands, or, as expressible geologically, that the regions 
from which material is being removed have less gravity than the regions 
over which material is now being loaded. Airy, in discussing the anoma- 
lies of the pendulum results, has suggested that the inferior gravity of con- 
tinental areas might be accounted for by the solid crust floating on a liquid 
lake. Stokes, however, as quoted in Pratt’s “‘ Figure of the Earth,” accounts 
for the anomalies in another way, viz., that the mass of continents above 
sea-level attracts the water upward along the shores of continents, and that 
the insular stations in which greater gravity is observed are really nearer 
the centre; in other words, that the sea-line is higher on continent shores 
than on island shores. Airy’s idea is quite in harmony with the subterra- 
neous conditions which I have been supposing. 

The conception of what may be called the topographical form of the 
thermal couches has certainly not received the weight it deserves in geologi- 
cal considerations. It is not at all impossible that the observed non-sym- 
pathy of contiguous voleanos might be because their vents communicate 
with the tops of domes or peaks of fusion, and that the activity might be 
of such a nature as not to communicate an impulse sufficient for ejection 
from one dome of fusion to another. 

In the above remarks, by fusion I have meant true igneous fusion, not 
the igne-aqueous liquidity held by Scrope—a theory interestingly stated 
by Stoppani.* It is my belief that the réle of water in determining the 
volcanic eruptions, and in the fluidity of lavas, has been greatly overestimated. 

Genesis OF VoLcantc Specres.—Whaiever may be the prevalence of 
opinion as to the genesis of volcanic rocks, modern microscopical research 
ought to have made it forever clear that a sharp line is to be drawn between 
the so-called Plutonic rocks and the true igneous ones. The inclusions of 
glass within the secreted minerals of volcanic species, the frequent presence 


* Bulletin de la Société Géologique de France. 186970, page 13/7. 
45 Kk 


706 SYSTEMATIC GEOLOGY. 


of isotropic substance wedged between the crystalline ingredients in 
greater or less amount in every one of the volcanic species, the frequent 
eruptions of molten glass, the relative ages of the glass magma and secreted 
minerals of innumerable volcanic masses, ought to have rendered it entirely 
clear that the original condition of each volcanic species prior to the forma- 
tion of the ingredient minerals and to ejection was that of a melted sub- 
stance in the nature of a glass. Arguments by Scrope, Lyell, and Stoppani,* 
in support of the theory that most, if not all, the secreted minerals of vol- 
canic rocks are formed subterraneously, lend a high degree of probability 
to the statement that few or none of the constituent minerals receive their 
crystalline form in the process of cooling after eruption. The microscopic 
demonstration of the inclusion by various minerals in volcanic rocks of 
portions of the glass magma, both before and after it has suffered the process 
of devitrification, confirms the view of subterraneous crystallization. Most 
ideas of the genesis of eruptive species start either with a melted magma or 
the igne-aqueous development of crystals. The adherents of hydrothermal 
fusion form a class of theorists who, in my belief, fail to appreciate sufli- 
ciently the gulf of difference which separates the true igneous rocks from the 
group embracing granite, syenite, and diorite. Led away by brilliant mod- 
ern synthetic results, they have come to believe that the subterraneous genesis 
of all crystalline rocks is paralleled by the artificial processes of Delesse, 
Deville, and others. They ought, at this stage of microscopic research, to 
be fully aware that all the volcanic rocks show abundant evidence of fusion 
in the presence of glass base and glass inclusions, while the group which is 
typified by granite never shows the slightest trace of the effects of fusion; 
that several of its constituent minerals are in a molecular condition, which 
they are known never to retain after an exposure to high heat; and, lastly, 
that every microscopical and macroscopical detail of these rocks allies them in 
their mode of origin to the crystalline schists which are, beyond all shadow of 
doubt, the results of low-temperature metamorphism of bedded sediments. 

The sole link which unites the granitoid family and that of the vol- 
canic rocks, young and old, is, that chemically they both lie within the 
rather elastic limits of the law of Bunsen. Richthofen’s argument, that the 


* Loc. cit. 


GENESIS OF VOLCANIC SPECIES. 707 


obedience of granite to this law at once relegates the birth-place of that rock 
to a couche below the sedimentary crust of the earth, is the only relation 
founded in fact which links the two crystalline series; but when we consider 
that the enormous body of Archean schists, including the gneisses, quartz- 
ites, dioritic schists, and limestones, are but the disintegrated products of 
older rocks, and that their special chemical differences represent mechanical 
and organic separations during the process of sedimentation, it is clear, first, 
that all the sediments are the result of disintegration and wearing down of 
the original crust of congealment formed of the molten surface of the earth ; 
secondly, that, therefore, as a whole, they represent precisely the chemistry 
of that crust, and if anywhere in the stratified crust a wide considerable 
body of these differentiated sediments were to be re-fused or commingled, 
especially if that solution or mechanical mixture took place in the early 
Archean horizons below the first appearance of limestone, the product, 
unless of most restricted dimensions, must necessarily represent something 
like the average chemistry of the primitive crust, and we need not, there- 
fore, be surprised to find the law of Bunsen asserting its sway over all 
remelted or extensively commingled rocks. 

If the theory to account for the origin of granite advanced in the second 
chapter of this volume is correct, that rock is simply commingled and meta- 
morphosed sediments, and would represent an approximation to an average 
of the sedimentary crust, and there seems to be no reason why the comming- 
ling of a considerable portion of the lower sedimentary crust might not repro- 
duce the chemical conditions of the average of the early crust of congeal- 
ment. It is no argument against this possibility to say that single beds of 
quartzite, of limestone, or gneiss do vary from the Bunsen law. Either 
in the case of granite or of any extensively developed lake of fused 
material the confinement of either fusion or metamorphism to a single 
one of the differentiated detrital beds of the crust is in the highest degree 
improbable. 

Waltershausen and Richthofen have given with greater definiteness 
than other writers the details of their conceptions of the interior conditions 
of the earth and the development of volcanic rocks. Waltershausen, in 


his ‘Volcanic Rocks of Sicily and Iceland,” from the specific gravity of 


708 SYSTEMATIC GEOLOGY. 


orthoclase, albite, quartz, crystalline limestone, and mica, derives a mean 
specific gravity for the exterior surface of the earth of 2.66. He assumes 
the mean density of the whole earth given by Reich as 5.45, a figure which 
the modern investigations of Airy and others have somewhat increased. 
He computes the central density of the earth at 9.585, or nearly equal to 
that of bismuth. He then estimates the actual pressure at different depths 
and at the centre of the earth, in these estimates assuming the earth to be 
in a fluid condition. For the geocentric pressure he computes 2,492,600 
atmospheres, from which he concludes that if the metals of which he con- 
ceives the greater part of the earth to be composed have their melting-point 
raised by pressure, as he thinks probable, the centre of the earth could 
hardly be fluid. 

If the temperature-gradient deduced by Thomson, or that which 
would naturally result from the empirical formula derived from observa- 
tion, may be relied on, as has already been shown when treating of fusion, 
the fusing-point must be enormously raised at the centre, and a very large 
part of the globe would probably be thus solidified. At the same time, in 
using the terms “solid” and “liquid,” it should be clearly understood that 
their significance, when applied to enormous temperatures and enormous 
pressures which appear in conjunction in the deeper parts of the earth, should 
necessarily be very seriously modified. It is in every way probable that 
the deeper regions of the earth are neither solid nor liquid in the sense in 
which we use those terms on the surface. The experiments of Dr. Andrews, 
on the passage of water from the fluid to the gaseous state under high 
pressures, offer instructive suggestions as to the possible mode of hypogeal 
transition between the fluid and the solid state. If we might confine our use 
of terms to “rigid” and ‘mobile,” our conceptions of the interior conditions 
might be rendered less indefinite. Waltershausen (translated) says: 

““We may conceive of the Earth either as a metal ball, fluid to the 
surface, or as having already entered the oxydized state. * * * It is 
then clear that in the outer crust the lightest bodies are particularly 
strongly represented, while the others need not be absolutely wanting. In 
the deeper layers, on the other hand, the heavier bodies will predominate 
and will seek to displace the lighter ones. Nearest the surface, silica, 


GENESIS OF VOLCANIC SPECIES. TO9 


potassa, and soda assert themselves, while lime, magnesia, alumina, and 
iron oxyd are present in comparatively small quantities. The gradual 
increase of the latter is accompanied without doubt by a decrease of 
the former to the extent of their complete disappearance. At still 
greater depths, besides the alkaline earths, alumina, iron oxyd, or mag- 
netic iron, new metallic oxyds will tend to increase the specific gravity 
of certain layers, until finally the pure metals—iron, nickel, cobalt, 
&c.—which remain in the depths unaffected by oxygen, have replaced the 
last oxyds. 

‘Now, as these different layers cool from the surface downward, there 
will gradually appear in them, without doubt, a different mineralogical 
character. Inasmuch as the silica as an acid combines with the mentioned 
oxyds to form the single or double salts, it is self-evident, without going 
further into the details, that in the upper layers acids or neutral salts with 
the separation of the acid (free silica) will be found, while in the deeper 
layers basic salts will gradually appear. While we look upon the earth as 
developed from a fluid mass, and can at least in general expect a continuous 
increase in the density from the surface toward the centre, it is unneces- 
sary that in the silicates of the different layers a continuous change should 
also be perceptible, or that all possible transitions from the acid through 
the neutral to the basic silicates should be found. Taking a certain group 
of more acid silicates as the superior, and a certain group of more basic 
silicates as the lower limit, all those silicates lying between can be consid- 
ered as transitions of the former into the latter, or as mixtures of the two. 
Taking into consideration the very slight differences in specific gravity 
which come in play here, and the density with which the silicates flow, 
especially at somewhat low temperatures, together with the size of the 
earth, a wholly homogeneous distribution of the separated elements and 
a perfectly regular increase of density towards the centre are not to be 
expected.” 

Basing his calculation on this increase of density, he derives the lavas 
of Aitna and Iceland from a depth of about seventeen geographical miles, 
from which level he estimates a required pressure of thirty thousand atmos- 


pheres as necessary to raise them. In his application of this increase of 


710 SYSTEMATIC GEOLOGY. 


density to the various volcanic species, and as a result of the preceding 
theory, he says: 

‘‘ Below the designated depth at which the formation of feldspar has 
reached its limit, augite will begin to predominate, attain its maximum, 
then gradually decrease, being replaced by magnetite; finally the magne- 
tite will predominate, and then, without doubt, be gradually replaced by 
the pure metals, especially by iron, nickel, and cobalt.” 

To sum up the theory of Waltershausen, the earth is a hot globe, of 
which a considerable portion is fluid, an unknown fraction of the centre 
having been rendered solid by the raising of its fusion-temperature by 
pressure. The downward increment of density is expressed by the chemi- 
cal increment of the heavy bases, and the fluid region directly under the 
crust consists, first, of a feldspathic and acidic magma which passes down- 
ward by successive replacements of bases into an augitic, and finally into a 
magnetitic magma. 

As far as Waltershausen’s idea of the sequence of volcanic species 
had progressed, this great shell of fused material answered the conditions 
of the natural succession upon the surface. The trachytic rocks were in 
general known to be ejected first, and the assumed superior position of 
the siliceous melted shell naturally accounted for their priority of eruption. 
The intermediate chemical grades of rock between the acidic trachytes 
and the basic basalts naturally were held to be products from interme- 
diate depths in intermediate time, and the general question of the genesis 
of species solved itself on the most simple laws. 

Richthofen, following Waltershausen in his assumption of a still liquid 
interior and of the great fluid shell of acidic and basic magmas, found 
himself confronted by a difficulty of his own making. Having established 
the remarkable natural periodic succession of his five orders of volcanic 
rocks, it was no longer possible for him to follow the simple law of time 
and depth on which Waltershausen rested. Richthofen, from his wide 
knowledge of natural succession, realized that if the melted shell of material 
was arranged according to its density, with the acidic magma overlying 
the pyroxenic,—since after the comparative basic extrusions of propylite and 
andesite the highly acidic trachytes and rhyolites had followed, and there- 


GENESIS OF VOLCANIC SPECIES. 711 


after the basic basalts,—the loci of eruption must have appeared earliest in 
the basic magma, then risen into the acidic, and lastly been depressed again 
into lower levels of the basie region. I have shown that the law of 
Richthofen was even more complicated than his own statement, and that 
there have been for each of the four orders an acidic, a neutral, and a basic 
period; in other words, if the interior is arranged in the two concentric 
(acid and basic) shells, with a neutral intermediate region, the theatre of 
eruption has been four times oscillated through the chemical cycle, since 
the acid and basic products alternate through the whole series of four 
orders. The difficulties which Richthofen encountered are thus increased 
fourfold. 

Whether we assume for the source of volcanic supply the general 
melted interior with its graded chemistry, as held by Waltershausen and 
Richthofen, or whether we admit the residual lakes of Hopkins, the diffi- 
culties presented by the remarkable alternation of acid and basic rocks in 
the full series of successive eruptions become absolutely insuperable on 
any physical laws which we can now apply. 

Richthofen* says in regard to the products of the volcanic era: 

“The conditions of the globe must have been very different in the 
Tertiary from what they had been in the Paleozoic period. A longer time 
of comparative repose had in most parts of the globe preceded the inaugu- 
ration of the violent manifestations of vulcanism in the Tertiary period than 
had ever before elapsed between any two eras of eruptive activity. The 
globe had cooled down. Volumes of sedimentary matter had accumulated, 
and added externally to the thickness of its crust, while it had increased in 
a vastly greater measure by the crystallization of liquid matter below. 
Those siliceous compounds, especially of low specific gravity, which had 
formerly yielded the material of the vast accumulations of quartziferous 
eruptive rocks, would have been consolidated, and the limit, as it were, be- 
tween the solid and the viscous state of aggregation receded into regions 
where the matter would be of a less siliceous composition and of greater 
specific gravity. The similarity in distant countries of the rocks first 
ejected (propylite and andesite) goes to show that the recession of that 


* Loe. cit. 


Wele2 SYSTEMATIC GEOLOGY. 


limit into greater depth must have proceeded in a nearly equal ratio in all 
those regions where volcanic rocks are distributed. When the tension 
below had increased sufficiently to overcome the resistance, it would now 
no longer manifest itself in the formation of small and differentiated systems 
of ruptures. In the direct ratio of the increase of the resistance, the frac- 
tures would have to be of greater extent, and those elongated belts of them 
would be formed which even now are partially distinguished as the belts of 
volcanic activity. The first rocks ejected necessarily would be of a more 
basic composition than the predominant rocks of the granitic era, while the 
repetition, at a later epoch, of the process of fracturing would give rise to 
the ejection of rocks in which silica would be contained in a still lower 
proportion. The greater portion, indeed, of the ejected rocks consisted of 
propylite and andesite in the first and of basalt in the second half of the 
voleanic era. A notable but only apparent anomaly in the regular order 
of succession has been the emission of trachyte and rhyolite between the 
andesitic and basaltic epochs. But if it is considered that these rocks were 
ejected partly from the same fractures through which andesite had ascended, 
and partly from others in their immediate vicinity, while the distribution of 
basalt has been independent, to a certain extent, of all foregoing eruptions, 
it is evidence that the occurrence of trachyte and rhyolite is closely depend- 
ent on that of andesite, and bears only a very remote relation to basalt. 
It appears that after the ejection of the chief bulk of andesite, when other 
processes ending in the opening of fractures into the basaltic region were 
being slowly prepared in depth, the seat of eruptive activity ascended 
gradually to regions at less distance from the surface. There is, within 
the limits of conjecture based on physical laws, no lack of processes which 
could codperate to that effect. The consolidation of the ejected masses 
within the fissures would probably proceed simultaneously, by loss of heat, 
from the surface downward, and, by pressure, from below upward. The 
opening of new branches from the main fractures, the remelting (by the 
aid of the heat of the molten mass within the latter, and of water finding 
access to it) of solidified matter adjoining the fracture, the emission of that 
remelted matter through those branches—all these are secondary processes, 


depending on the first almost necessarily. The supposition that to these is 


GENESIS OF VOLCANIC SPECIES. file 


due the order of time in which trachyte and rhyolite have been ejected to 
the surface, is corroborated by the fact that these rocks oceupy generally a 
subordinate position in regard to quantity, and have had, to a great extent, 
their origin in volcanic action.” 

In this are two assumptions which the extensive field of the western 
Cordilleras does not bear out: First, that the distribution of basalts has 
been independent of the other prior eruptions; secondly, that trachytes 
and rhyolites are subordinate in their quantitative relations to either the 
andesites or the basalts. As I have already shown, the reverse of both 
propositions is the rule over the western United States. 

According to Richthofen’s views of the succession in the case of tra- 
chyte and rhyolite, “the seat of eruptive activity gradually ascended to 
regions at less distance from the surface”; but with the fuller expression 
of the law of succession the theatre of eruption must have oscillated four 
times toward the surface and down again. 

Upon the theory of a general molten interior with graded chemical 
shells, the actual vertical distance of this oscillation of the seat of eruptive 
activity would have to be very great, owing to the extremely slow downward 
change of density. For the locus of eruption to pass from the level, for 
instance, of the mean density of augite-andesite up to that of the most 
acidié trachytes, would be to traverse a wide range of the molten shell, 
and this distance would necessarily have been traversed eight times in the 
volcanic age. 

Another strong argument weighs against the conception of a general 
liquid shell. When we come to compare the nature of the true igneous 
rocks of pre-Silurian time, like those which are exposed on so grand a scale 
in the region of Lake Superior, we find eruptive quartz porphyries and 
eruptive diabases and melaphyres whose average chemical constitution and 
specific gravity differ very slightly from that of the quartz-porphyries and 
diabases of Jurassic age, as shown in the eruptions of the Cordillera sys- 
tem, and they also betray but very slight chemical and specific-gravity 
differences from the rhyolites and basalts of the Pliocene and post-Pliocene 
eruptions. Upon the theory of a generally melted interior, all the rocks 


of a given specific gravity and average chemical composition must have 


714 SYSTEMATIC GEOLOGY. 


come from about the same couche. The basalts, augite-trachytes, augite- 
andesites, augite-propylites, middle-age diabases and pre-Silurian diabases, 
and melaphyres, representing comparatively similar expressions of the 
pyroxenic magma, must all necessarily come from a single subterraneous 
shell. 

Considering, then, the acidic rocks, we have the rhyolites, quartzifer- 
ous trachytes, dacites, quartziferous propylites, middle-age quartz-porphy- 
ries, and Archzean quartziferous erupted species, representing a second set 
of products having a close chemical equivalency and almost uniform specific 
gravity. On the theory of Waltershausen, they, too, must have come from 
one and the same acidic couche. ; 

Carrying back these two types into the very earliest (Azoic) division of 
geological time, it will be evident that the theatre of eruptive activity must 
have been throughout this whole enormous interval oscillating back and 
forth between two permanent trachytic and pyroxenie shells. 

If the earth is a hot body undergoing secular refrigeration, and if 
these rocks, separated by such enormously wide intervals of time, have 
come from two permanent shells, as they necessarily must have come, on the 
theory of Waltershausen, then not only has secular refrigeration failed to 
congeal the uppermost shell, but it must have remained permanently melted 
over the pyroxenic shell, and all pyroxenic eruptions must have been forced 
to the surface through the superincumbent melted acidic shell. Either this 
long-continued oscillation from shell to shell, or, in view of the secular re- 
frigeration, the permanence of these shells, or the eruption of pyroxenic 
material upward through the siliceous shell, involves physical difficulties 
which appear to be altogether insuperable. Furthermore, the arguments 
of physical astronomers against any general interior fluidity remain abso- 
lutely unassailed, and those who have derived the eruptive rocks from such 
a general fluid interior, or from any deep intermediate fluid shell between 
the rigid interior and a congealed crust, have, besides their other difficulties, 
to answer the arguments for the earth’s rigidity, which they have never 
even attempted to do. 

If, however, either on the theory of Mallett, which I totally reject, or on 
the hypothesis of the origin of fusion which I have introduced in the pre- 


GENESIS OF VOLCANIC SPECIES. 715 


ceding pages, or by any other means, temporary local lakes were formed 
resulting from the fusion of a thin shell of the crust, it would seem that the 
arrangement into two zones—a lighter overlying a heavier one—would from 
the nature of things gradually assert itself within the limits of the enclosed 
fused region. 

In the law of succession, as I have stated it in the previous section, in 
eacn order the augite eruptions are the later. The same is true as between 
the middle-age porphyries and diabases of Europe, and the law holds 
equally good as between pre-Silurian quartz-porphyries, diabases, and mela- 
phyres of the Lake Superior region. If, therefore, according to my suppo- 
sition, fusion is a function of erosion, and each order is the result of a definite 
period of erosion, and becomes thus an expression of a recurrent phase of 
geological history, each fused lake may have its double period of eruptive 
activity, the acidic magma coming to the surface first, followed by the 
pyroxenie. 

The meaning of this succession seems to be, that wherever fusion is 
developed on a considerable scale, by whatever mode, the fused material 
divides itself into two parts, the acidic or lighter coming to the surface be- 
fore the basic and heavier. There are two methods by which this separation 
within the limits of a fused lake might be made: first, while in a state of 
fusion, on well understood principles, the heavier liquid might concentrate 
at the bottom of the lake, leaving a supernatant couche of lighter matter ; or, 
secondly, in the act of crystallization, which all present facts tend to prove 
is a subterraneous process, the actually formed crystals might separate them- 
selves according to their differences of specific gravity. It is true that, as 
between minerals composing the acidic species and those entering promi- 
nently into the constitution of the basic species, there are no great differ- 
ences of specific gravity; but they are amply sufficient to permit the free 
movement of the crystals through the containing magma. 

Darwin, in his “Volcanic Islands,” gives an interesting account of a 
certain basaltic flow in the Galapagos Islands, in which he observed that 
the developed crystals had sunk to the bottom of the lava, leaving the 
upper portions comparatively free from visible minerals. In my own studies 


of the lava streams of Hawaii, I have frequently repeated the same obser- 


716 SYSTEMATIC GEOLOGY. 


vation. During eruption in the crater of Kilauea, at the time of my 
visit, a fluid stream of basalt overflowed from the molten lake at the west 
end of the crater and poured eastward along the level basaltic floor of 
the pit. Numerous little branchlets spurted out from the sides of the flow 
and ran along the depressions of the basaltic floor for a few feet and then 
congealed. I repeatedly broke these small branch streams and examined 
their section. In every case the bottom of the flow was thickly crowded 
with triclinic feldspars and augites, while the whole upper part of the stream 
was of nearly pure isotropic and acid glass. 

Scrope it was who originally suggested that within the limits of fused 
lakes a specific-gravity separation might take place by the sinking of all erys- 
tals heavier than the magma, and the rising of all lighter. Lyell and Darwin 
have approved of this theory, and Darwin, in his ‘“‘ Volcanic Islands,” gives an 
extremely clear statement of the modus operandi of such separation. Richt- 
hofen, in a note in his ‘‘Memoir,” page 34, rejects this idea of the genesis 
of voleanic species, deriving his objection from the curious periodic suc- 
cession of voleanic species. In his conception, however, all of the Ter- 
tiary volcanic rocks came from one melted interior, and under that belief 
it is natural that he should have seen the impossibility of a specific-gravity 
arrangement which could account for the interpolation of trachytes and 
rhyolites between andesites and basalts. 

Under my hypothesis, by which fusion is the temporary result of ero- 
sion, each one of Richthofen’s orders, with its acidic and pyroxenic mem- 
bers, would be considered as the product of a single ephemeral lake. A 
period of erosion, under this conception, would result in the formation of 
a lake. The cessation of erosion, either from climatic causes or from the 
degradation of centres of erosion, would place a limit to the expansion in 
depth of fusion; in other words, would define the time-limits and the ver- 
tical expansion of the lake. Refrigeration, continuing from that time, would 
result in the crystallization of the various mineral species. As between 
the minerals entering the composition of the acid rocks and those of basic 
rocks, there is, according to my belief, a sufficient difference of specific 
gravity to account for the separation. The magma through which they 


moved in the process of separation, and which lingers in the intercrystalline 


GENESIS OF VOLCANIC SPECIBS. Fly 


spaces, is partly the isotropic glass which imbues the groundmass and consti- 
tutes the base of the various species, partly the groundmass itself. Since 
this separation would be an affair of some time, and the causes which de- 
termined eruption might supervene when crystallization had begun and 
before specific-gravity separation had completed its work, it would be 
natural to expect that eruption would frequently occur before the complete 
genesis of species. In my view, the latest lake of fusion after gravity-sep- 
aration would result in a layer of rhyolite floating upon a layer of basalt; 
and if before this separation into rhyolite and basalt an eruption took place, 
its products should contain the combined minerals of rhyolite and basalt. 
Accordingly we do find, as in the great field of so-called trachytes in the 
region of the Elkhead Mountains, an enormous outflow, composed of free 
quartz, sanidin, and biotite, (the materials of rhyolite), commingled with tri- 
clinie feldspar, augite, and magnetite-iron, (the materials of basalt). Sup- 
posing a separation to have occurred between these two sets of minerals, 
from the chemistry of this rock, which places it as to its acidity near the 
lowest limits of the trachytic magma, a large proportion of rhyolite and 
a small proportion of basalt would have been formed. Wherever a molten 
lake should be formed within the acidic shells of the earth, after separation 
by specific gravity the relative proportions would show a great preponder- 
ance of the acidic member. 

In the remarks, in the previous section, on the quantitative proportions 
of all the eruptions of the volcanic rocks of the Fortieth Parallel area, it 
was shown that the acidic members do greatly outweigh the augite mem- 
bers; but, on the other hand, there are numerous localities where there is 
either none at all or very little of the acidic members, and a large amount 
of an augite rock. In explanation of this frequently observed condition, it 
should be said that the position of the acidic layer within the lake on the 
top of the augitic shell exposes it first to the effects of refrigeration. Pro- 
vided there is no eruption, the history of a fused lake will be this: First, its 
secreted minerals will separate themselves by specific gravity ; secondly, as 
a result of secular refrigeration the upper surface of the lake will congeal, 
and this solidification will proceed downward. It might easily proceed 
throughout the entire depth of the acidic zone before an eruption took 


718 SYSTEMATIC GEOLOGY. 


place, in which case the first appearance at the surface would be from the 
augite magma, or in extreme cases it might wholly congeal in situ. 

The rocks of mean composition might be formed in two ways: if at 
any time before the specific-gravity separation, eruption should occur, a 
chemical mean product would be obtained, containing the minerals of both 
the acidic and the basic magmas; on the other hand, after separation had 
occurred, and when the entire lake was arranged in zones according to the 
specific gravity of the ingredients, between the masses of highly acidic 
rocks and the most basic would be an intermediate layer, which in case of 
eruption would produce one of the transition-types provided for by the 
law of Bunsen. 

In the secular refrigeration of the globe these temporary lakes of fusion 
would necessarily occur at greater and greater successive depths. The 
deepest of all would be the latest (neolite) lake, and the secular changes 
that recorded themselves in the subtle petrographical distinctions by which 
the various acidic and basic members can be distinguished inter se, are in 
each case the expression of depth. 

Hopkins’s method of accounting for the maintenance of his residual 
fused lakes by their superior fusibility to the surrounding crust, might 
possibly account for liquid augitic lakes surrounded by siliceous boundaries; 
it could not account for the presence of siliceous lakes; whereas I submit 
that the formation of lakes underneath the points of maximum erosion, the 
subterraneous crystallization of minerals within the melted magma, and 
their final separation by specific gravity, account for all the complicated 
phenomena of periodic succession of volcanic rocks, with their astonishing 
time-oscillations between the acidic and the basic magmas. 

Besides the theory of Waltershausen, and that here advanced, there is 
the often discussed possibility of a separation by liquation. That process 
might be supposed either to act upon regions of relatively low fusibility, or 
in composite rocks of the granitic type by the melting of the more basic 
and fusible minerals, leaving the others, which are lighter and less fusible, 
to float upon the surface of the fused basic material; but upon any such 
hypothesis the formation of mixed rocks like the Elkhead trachytes, which 
contain the minerals of rhyolite and basalt, would be unaccounted for. 


GENESIS OF VOLCANIC SPECIES. 719 


Doubtless in the actual process of fusion there is sometimes a quasi action 
of the law of liquation, by which certain peculiarly infusible minerals might 
altogether escape solution in the fluid magma. It has seemed to me that 
in the case of the quartz-propylites such an accident might account for the 
presence of granules of quartz containing fluid inclusions, sometimes double 
inclusions of water and liquid carbonic acid, in the strictly voleanic ground- 
mass, by supposing the quartz granules to be fusional survivals. The same 
supposition would account for the presence of apatite with fluid inclusions 
in rhyolite. 

A further feature of the minerals of the various volcanic species might 
be held to be accounted for by the specific-gravity theory. Zirkel has 
shown, in his study of basalts, that numerous augite crystals are made up 
of a dense crowd of magnetic iron grains held together by augitic magma, 
the whole group lying within the figure of an augite crystal. In the more 
basic basalts many of the augites are thus three quarters made up of mag- 
netic iron; when, however, in acidic trachytes or dacites or quartz-propy- 
lites, augites are observed, they are always of a pale green or pale yellow- 
green section, and generally are totally devoid of the included accumula- 
tions of magnetite grains. The wide differences of specific gravity and 
iron tenure within the species augite in volcanic rocks is largely to be 
accounted for by the presence of these foreign grains, and it is not unin- 
teresting that the highly magnetiferous augites are confined to the most 
basic rocks, while all the accessory augites of the acidic rocks are of pale 
color and slight specific gravity, and are free from included iron grains. 

In accounting for the assemblages of minerals which go to make up 
the various species on the ground of specific gravity, the greatest difficulty 
is found in the case of mica, which varies from 2.7 to 3.1. Here again the 
heaviest micas are found in basalts, the lightest in rhyolites; but to 
account for either mica or hornblende in the presence of the light minerals 
of rhyolite it is necessary to suppose that they failed to sink and work their 
way down through the crowd of other crystals to the level to which their 
specific gravity would naturally take them. Now, in the water-separation 
of minerals of granite, as constantly observed in areas of granite decom- 
position, feldspar and quartz, from the forms of their particles, settle most 


720 SYSTEMATIC GEOLOGY. 


rapidly, while the mica flakes, although of a higher specific gravity, from 
the shape of the particles, continue to float; so that rivers like those which 
descend the west slope of the granitic Sierra Nevada carry an abundance 
of sparkling mica flakes long after they have dropped their load of quartz 
and feldspar sands. It is doubtless the flat forms of mica and of the broad 
earthy hornblendes which account for their presence in eruptions from 
the lighter magmas. 

One of the most common features of a wide family of basalts is the 
presence in the interstices between the crystals of plagioclase and augite 
of a highly acidic glass. We have seen that in the lava streams of Ha- 
waii the few included crystals of plagioclase and augite sank to the bot- 
tom of the stream, and that the principal part was glass. One of the 
most remarkable features of that classic locality is the rivers of nearly 
crystalless glass-lava which have flowed from an upper crater, distances of 
thirty and forty miles, to the sea. The occurrence of such volumes of vol- 
canic glass can be accounted for by the supposition of a lake in which the 
specific-gravity separation has taken place, and the acidic supernatant 
stratum been drawn off by early eruption or congealed, the residual portion 
consisting of acidic glass, whose specific gravity is less than that of the 
plagioclase or augite. In that case those minerals might sink, leaving an 
upper stratum of erystalless volcanic glass, which, when erupted, in the 
process of cooling after eruption might develop only those minute crystal- 
litic forms which the microscope discloses in all the glassy lavas. The 
supposition of Stoppani that all volcanic glasses are the result of a mole- 
cular change posterior to eruption has absolutely nothing to warrant it. 

As bearing upon the character of subterraneous lava lakes, the 
breccias should be mentioned. Among the early eruptions of all the 
volcanic series breccias are given. They usually consist of sharp angular 
fragments, between which is a magma of the same material. Sometimes 
the fragments are confined to the size of a marble, and again they 
reach large masses weighing several tons, but with the exception of ob- 
viously foreign inclusions the fragments and magma are the same. There 
is nothing in the appearance of these breccias which warrants the idea that 
the fracture took place after the eruption Frequently, as between the con- 


CLASSIFICATION OF VOLCANIC ROCKS. 721 


taining matrix and the fragments, there are characteristic differences in mode 
and scale of crystallization. It is in every way probable that the breccias 
were subterraneous products, that they were crushed in depth, and never 
remelted, but were given their fluidity by a still liquid magma which flowed 
in and occupied all the interstices between the broken fragments. I have 
before maintained that in the process of secular refrigeration and in the 
absence of the active causes of eruption the uppermost layers of the molten 
lake would gradually undergo congealment. The upper strata of the acidic 
lavas, having become solid, would easily crush under any of the unusual 
tangential strains to which the crust is from time to time exposed, and with 
the supervention of the causes of eruption the crushed fragments would be 
swept out with more or less matrix as a subterraneously formed breccia. 
It is also to be noted that while breccias are very common among the acidic 
members of the various orders, they are less common among the augitic 
representatives of each order. 


CuassiricaTion oF Vouicanic Rocxs.—The reader will now perceive 
the grounds on which I have coupled two such diverse products as rhyo- 
lite and basalt in one order. Regarded chemically, their divergence is no 
more noticeable than that of the early diabases and quartziferous porphyries 
of pre-Silurian time; and the petrographical characteristics of the two rocks 
are not more widely different than are black augite-andesites from dacites 
or black augite-trachytes from the quartziferous member. In this view, 
the remarkable and hitherto inexplicable natural sequence of volcanic 
species becomes comprehensible, and basalt and rhyolite, grouped together 
as the order neolite, become the last couple or latest formed lake. 

It is unnecessary here to repeat the admirable expressions of diagnos- 
tic points by which the various orders and their subdivisions may be sepa- 
rated. Richthofen, in his classie memoir, and Zirkel, in his various contri- 
butions, including Volume VI. of this series, besides many other German 
petrographers, have clearly shown upon what permanent and essential differ- 
ences rhyolite, quartziferous trachytes, dacite, and quartz-propylite may be 
separated, and the petrographical points by which basalt, augitic trachytes, 
augitiec andesites, and augitic propylites may be distinguished. If the 

16 K 


722 SYSTEMATIC GEOLOGY. 


hypothesis of the formation of independent lakes of fusion as a function of 
erosion and of the subterraneous specific-gravity separation into two groups 
shall finally be accepted, I submit that the natural succession of volcanic 
rocks forms, as Richthofen has already indicated, the true basis of a final 
classification. The characteristic differences between what Richthofen has 
called orders, become then expressions of time, of depth, and of pres- 
sure, since with the secular recession of temperature the critical shell 
in which fusion would be induced by erosion must constantly retire from 
the surface downward, and the latest order, neolite, would hence repre- 
sent the deepest development of a lake. An entire lake, under this view, 
would bear a relation to its differentiated products not very dissimilar to 
that which the biological term “genus” bears to its subordinate “species.” 
I propose, therefore, that to each lake or order of Richthofen the term 
“‘oenus” should be applied, and to the differentiated products, “ species.” 
Genera thus become expressions of time and depth, and species the chem- 
ically differentiated products due to specific gravity. Within the range of 
each species there is, as every petrographer well knows, the widest range 
in texture and physical properties. Consider, for instance, the species rhy- 
olite, which may appear as a nevadite entirely made up of crystalline 
minerals, with only the slightest traces of vitreous binding-material, or at 
the other end of the scale of texture may appear as a uniform isotropic 
obsidian with only the minutest crystallitic inclusions. These variations, 
altogether within one normal chemical constitution, become the varieties 
of the species, and it is submitted that any one species may, under favoring 
physical circumstances, appear through the whole range of varieties from 
entire crystallization to pure glass. It is true that thus far glassy propylites 
have not been described, but there is probably nothing in the nature either 
of the depth in which they were formed or of their chemical constitution to 
prevent the formation of the glassy types. Of the genus andesite, all three 
of the species—dacite, hornblendic, augitic—have been described as contain- 
ing more or less glass. In the genus trachyte, both the extreme varieties 
show in their microscopic features the presence of glass. In the ordinary 


sanidin-trachyte, that glass has generally undergone the process of devitrifi- 
cation or is full of ferrite and opacite, yet, both in the black augite-trachytes 


CLASSIFICATION OF VOLCANIC ROCKS. 723 
and in the sanidin varieties, there are occasional large developments of pure 
glass. Within the genus neolite, in both species, basalt and rhyolite, is the 
greatest development of glass, and the entire chemical range of the species 
basalt is also represented by glasses varying from the basic tachylite to the 


relatively acidic hyalomelane. 


In conformity with the views thus expressed, 


I propose the following classification of volcanic rocks : 


CLASSIFICATION OF VOLCANIC ROCKS. 


TERTIARY FAMILY. 


GENERA. 


Expressions of time according to 
Richthofen’s Law of Succession, 
and of dopth owing to secular 
refrigeration. 


SPECIES. 


Expressions of chemical differentiation by specific | 


gravity of mineral ingredients, grouping under 
the Law of Bunsen. 


VARIETIES. 


Expressions of range of texture 
according to predominance of se- 
erected crystals, groundmass, or 
base. 


PROPYLITE. 


Quartz-Propylite. 
Hornblende-Propylite (rarely 
micaceous). 


Augite-Propylite. 


ANDESITE. 


Varieties wholly dependent on 
quantitative relations of secreted 
crystals and groundmass (no bass 
yet observed). 


Dacite. 

Hornblende-Andesite 
micaceous). 

Augite-Andesite. 


(rarely 


TRACHYTE. 


NEOLITE. 


Quartz-Trachyte. 

Mica-Trachyte (rarely horn- 
blendic). 

Augite-Trachyte. 


Varieties dependent on quantita- 
tive relations of secreted crys- 
tals, groundmass, and base. 


Varicties dependent on quantita- 
tive relations of secreted crys- 
tals, groundmass, and base. 


Quartz-Rhyolite (nevadite). 

Mica-Rhyolite (very rarely 
hornblendic). 

Basalt. 


Varieties dependent on quantita- 
tive relations of secreted crys- 
tals, groundmass, and base. Iso- 
tropic base far exceeds that of 
any other genus. 


724 SYSTEMATIC GEOLOGY. 


This will be seen to deviate but slightly from the scheme of Richt- 
hofen, substituting the word “genus” for his term “ order,” and following 
exactly his time-scale of periodic succession, but throwing together into 
the genus ‘‘neolite” the hitherto separated rhyolite and basalt. The part 
in this classification played by the law of Bunsen is, that that principle 
governs the range of chemical constitution of species within the limits of 
each genus. The part played by the remarkable law of Richthofen is, that 
it places the various genera of volcanic products in their natural time- 
order. 

The oldest genus, propylite, differs from the next succeeding genus, 
andesite, and indeed from the three other genera of the family, by two im- 
portant mineralogical characteristics: first, as Richthofen early pointed out, 
the character of the propylitic hornblendes, which are green like those of the 
earlier diorite, and are made up of microlitic staffs, and hence not cleav- 
able on crystalline planes—a feature which extends through the whole 
genus, and seems to be a survival of the earlier types of hornblende; 
secondly, the abundant quartz of the quartziferous member carries fluid 
inclusions and no glass, thus further linking the genus with the long ante- 
rior diorites. 

With the genus andesite first appears a cleavable brown hornblende 
surrounded by a characteristic black border, and the quartz of the dacites 
caries glass inclusions but no fluid. 

Mica, rarely replacing hornblende in propylite, appears among the 
andesites in rather more noticeable proportions; and with the andesites also 
comes in abundant glass, both as inclusions within the bodies of erystals 
and as a base imbuing the groundmass. 

With the trachytes mica far exceeds hornblende. Quartziferous mem- 
bers are rare, and the quartz is always present as macroscopic secreted 
granules, but never enters the constitution of the groundmass. <A notice- 
able feature of ejections which have been classed as trachytes is the occur- 
rence of what appears to be the non-separated neolite magma, representing 
a period after the secretion of crystals, but before their separation by 
specific gravity. This is perhaps to be accounted for by the supposition 
of extreme viscosity near the temperature of congealment or of a rather 


CLASSIFICATION OF VOLCANIC ROCKS. T25 


heavy magma, wherein the crystals of mica, augite, hornblende, and sani- 
din would have less tendency to move than in a melted magma of lower 
specific gravity. It might also be explained by active convection within 
the lake, which prevented separation of minerals. 

The augitic species of each of the first three genera are rare, and their 
volume inferior to their companion species. Within the genus neolite the 
most perfect separation seems to have taken place, only the very rarest 
augite appearing in rhyolite. In the genera propylite and andesite, 
throughout the whole range of species, triclinic feldspars exceed the sani- 
din, and hornblende exceeds mica. In the two later genera, with the single 
exception of the earliest trachytes, mica exceeds hornblende, and in the 
quartzitic members sanidin exceeds triclinic feldspar. While the quartz- 
iferous members of each group approach the same tenure of silica, the augite 
members grow steadily more basic up to the point of the heaviest basalts. 


‘ 


CHAPTER AV LiL: 
OF O GAAP HY, 


ARUHZAN — POST-CARBONIFEROUS — PostT-JURASSIC — Post-CRETACEOUS — TER: 
TIARY — CONCLUSION. 


For a comprehensive discussion of the general orographical problems 
presented by the Fortieth Parallel Exploration, nothing less than the full 
dimensions of a volume like this would suffice. In this brief final chapter 
I purpose to do no more than chronicle the succession of the grander dy- 
namic events, and give such current notes of their date, area of operation, 
and general characteristics as shall enable the reader to correlate the me- 
chanical history of our section of the Cordilleras with the great strata-sec- 
tion outlined in previous chapters. 

On the one hand, it is to be regretted that such condensation is required 
by the construction of this volume; on the other, I am compensated by 
the consideration of our provokingly defective knowledge of the very rudi- 
ments of terrestrial thermodynamics, from which alone we might hope to 
bridge the chasm still separating our phenomenal knowledge from the 
vague land of causes. 

Already in the previous chapter, while advancing and discussing a 
hypothesis to explain hypogeal fusion and the genesis of volcanic species, 
I have trodden far enough, perhaps too far, on the thin crust of physical 
conjecture. 

It is my general belief that the suggestions of Herschel and Babbage 


as to the reactions upon the hot interior from superficial transportation will 
727 


728 SYSTEMATIC GEOLOGY. 


yet prove to be a key for unlocking some of the closed doors of geological 
dynamics, but it is useless to pursue this line of investigation as mere 
speculation. 

In spite of the discrepancy between different determinations of the co- 
efficients of contraction, it is apparently quite within the range of probable 
physical experiment to determine the true differences of specific gravity 
between volcanic products in their fused and in their congealed state, and to 
obtain the latent heat of fusion of the same materials. Their specific heat 
has in many instances been already satisfactorily obtained, and we are in 
possession of a formula by which to ascertain the pressure at any subterra- 
nean point. With these constants and an approximation to the temperature 
of fusion, we shall be able to reach, by a formula akin to that of Prof. James 
Thomson on the quantitative lowering by pressure of the freezing-point of 
water, a determination of some value on the nature of that critical shell of 
fusion which I have advocated as a possibility, and the quantitative amount 
of deepening and shallowing which that liquid shell would suffer by known 
loading or unloading of the surface. 

In addition to a knowledge of the laws of contraction of the globe, it 
is required to ascertain not only the conductivity of rocks but the different 
rates of conductivity of given materials in the solid and in the liquid state 
at the same temperature. 

Firmly convinced that the phenomena of the geological section are 
expressive of two laws—the statics of the revolving sphere, and the dissipa- 
tion of energy from its original and existing inner temperatures, and grant- 
ing the rigidity required by the tidal argument, I find, until the hypothesis 
of a critical shell within an immediately superficial region of the globe and 
the effect upon that shell by the processes of degradation and transporta- 
tion are disposed of, no physical suggestions whose probable, not to say pos- 
sible, application could account for the known operations of the crust. 
Mere deformation of a solid globe under tangential strain is totally inade- 
quate to account for a vertical fault of 40,000 feet, nor does it explain 
the remarkable historic sequence by which loaded regions gradually sub- 
side foot for foot, while regions lately unloaded subside paroxysmally. No 
theory of the expansive force of imprisoned elastic gases can account for 


OROGRAPHY. 729 


the variability of upheaval and subsidence. And, lastly, no strictly chemi- 
cal theory yet advanced, when brought into contact with stubborn facts, 
has the slightest shadow of applicability. I can plainly see that, were the 
critical shell established, its reactions might thread the tangled maze of 
phenomena successfully, but I prefer to build no farther till the under- 
lying physics are worked out. I therefore refrain from a discussion of the 
causes of crust-motion, but in the interest of the completeness of this vol- 
ume as a piece of history give a short and rather cursory examination of 
the mechanical phenomena, leaving their minute discussion to a day in the 
near future when it can be done on a firmer physical foundation 


ArcH&AN Orocrapuy.—The extended section embraced within the 
Fortieth Parallel area offers abundant evidence of repeated periods of oro- 
graphical disturbance separated by intervals of comparative calm. 

It has been already shown in Chapter IJ. that beneath the post- 
Archean covering of rocks lies a tremendous mountain system built up of 
folded and faulted ranges of Archean rocks If the whole series of unal- 
tered sediments from the bottom of the Cambrian were to be removed, we 
should come upon the most remarkable mountain system which has been 
thus far developed in the world. 

The Archean sediments, of which perhaps 60,000 feet have been rec- 
ognized in two great groups separated from each other by a period of dis- 
turbance, represent stratified rocks in a most extreme state of compression. 
In comparing the changes of thickness and accompanying physical condi- 
tion of various of the later strata, it has been seen that between the loosely 
ageregated state of a newly made sedimentary bed, and the more compact but 
still uncrystallized condition of the same bed, there may bea diminution of 
half the original thickness. In passing from the compact condition to the 
highly erystalline state of the Archzean schists, there would doubtless be a 
still further very great loss of thickness of beds. It is safe to say that 
the 60,000 feet of Archean sediments represent an original thickness of 
120,000 feet of uncompacted sediment. Indeed, they probably represent 
nearer 150,000. 

It is evident that all these rocks were altered into their present erystal- 


730 SYSTEMATIC GEOLOGY. 


line condition prior to their being folded up into mountain ranges. This is 
proven from the fragments of the bedded schists that are enveloped in 
plastic granite, which appears as distinct intrusions in rifts and fractures of 
the crystalline beds, caused at the time of their folding and upheaval. The 
included fragments of stratified schists, lying like islands within the gran- 
ite, often have a length of 1,000 to 2,000 feet, and their physical 
condition, their state of crystallization, and even the minutest micro- 
scopical characteristics of their component minerals, are precisely the same 
as the solid masses of schist into which the granite intruded. They were, 
therefore, crystalline rocks prior to their upheaval. In view of the neces- 
sary compression required to convert a bed of arkose sediments into a 
crystalline schist, it is evident that when crystallized these Archean beds 
must have been overlaid by a very great thickness of rocks, which in gen- 
eral remained unaltered and have been entirely swept away, leaving no 
traces except evidence of their former downward pressure. 

The actual orographical features of the Archeean ranges correspond 
very closely with those of modern manifestations of the same forces. 
Colorado Range, for instance, is a broad, single anticlinal thrown into a 
low, flat arch. Medicine Bow and Park ranges were also anticlinals. The 
three together form a folded group of ranges which prior to Cambrian time 
were deeply dislocated. The anticlinal of Park Range was cleft down 
the axis, and the eastern half depressed at least 10,000 feet. Colorado 
Range was severed by an enormous southeast-northwest fault, which 
dropped the region of the Laramie Hills 6,000 or 7,000 feet lower than 
the southern continuation of the same ridge. 

At the little Archzean body on Red Creek, in the northern foot-hills of 
the Uinta, was a precipice, the result of a fault of which we now recognize 
10,000 feet, the bottom and top having never been reached. 

The inclined easterly dipping Paleeozoic and Mesozoic rocks of the 
Wahsatch, in the region of the Cottonwood, rested against the abrupt pre- 
cipitous face of a granite cliff, of which 30,000 feet are now exposed. 

West of the meridian of the Wahsatch there has been so much crump- 
ling and vertical faulting since Archeean time that it is very difficult to sep- 
arate the earlier effects from subsequent ones. It is only possible to recon- 


OROGRAPHY. 731 


struct the Archzean topography and orography from the limited exposures 
of the early rocks which occur in the various ranges. They were evidently 
folds of crystalline schists which here and there had suffered abrupt fault- 
ing, and which toward the west were more and more invaded by successive 
intrusions of the four granite periods. 

Tangential strains resulting in folds, and radial strains resulting in ver- 
tical faults, are the general characteristics of the orography of the Archean 
age. In observing the contact of the Paleozoic strata where they abut 
against the old Archzean slopes, it is seen that the ancient surface in the 
region of contact of crystalline schists and granite had been planed down 
by a very general erosion. 


Post-CarBONIFEROUS OrocrapHy.—The entire Paleozoic time over 
the Fortieth Parallel field was an age of subsidence, of sedimentation, 
and of rest from orographical disturbance. I have before shown that 
the main source of detrital material for the thickest development of Palzeo- 
zoic rocks was an elevated and extended land-mass which rose in western 
Nevada about the meridian of Havallah Range. Directly east of that 
land-mass the thickest body of Paleozoic sediment, of 40,000 feet, was 
formed. Between the different beds of the Paleozoic are none of those non- 
conformities which in the Appalachian field denote orographical movements. 
After the folding of the Archean ridges there was no mechanical violence 
until the close of the Carboniferous age. The movement which then took 
place has been already briefly described as a necessary step to the compre- 
hension of the general grouping of sediments; but the exact physical 
character of that disturbance is one of the most puzzling and most interest- 
ing features of the orographical history of the whole region. 

The Paleozoic sediments having accumulated against that western 
shore 40,000 feet thick, a fault occurred reversing the arrangement of land 
and water. The ocean bed became the land, and the former land sank to 
avery great depth, becoming the bottom of an ocean, in which 25,000 feet 
of Mesozoic rocks accumulated. The marked and peculiar feature in this 
occurrence is the fact that the region which went down was the region which 
had been unloading during the entire Palaeozoic. Throughout the Paleozoic 


(py SYSTEMATIC GEOLOGY. 


series are evidences of repeated subsidence in the occurrence of sheets of 
conglomerate which could only have been transported in comparatively 
shallow water. We have here, therefore, two types of subsidence: 

First, the long recognized type of a loaded area displacing subjacent 
crust and sinking into the solid earth, a process which suggests the mere 
restoration of statical equilibrium. It is evidently gradual, and comparing 
depth of subsidence with thickness of deposit, it is seen that sinking is in 
the direct proportion of volume. ‘This type of subsidence, so justly insisted 
on by James Hall in the case of the Appalachian Mountains, is here paral- 
leled on a wider scale, the area of great subsidence being much broader 
than that of the Appalachian system, embracing a width of not less than 
500 miles. 

Secondly, when, at the close of the Palzeozoic, the land-mass began to 
subside, its area, lightened of the whole of the Palzeozoic sediment, went 
rapidly down by a distinctly catastrophic process analogous to that of the 
modern faults which are seen to form in earthquake regions. The sudden 
sinking of an area which has been relieved of a considerable portion of its 
load bears, of course, no relation to the equilibrium of the figure of the 
earth, but its origin must be sought in the obscurity of geological ther- 
modynamics. With the subsidence and accompanying oceanic submerg- 
ence of what had been the Paleozoic land, came the emergence of the 
thickest portion of the Palzeozoic ocean beds, which was rapidly lifted 
above the water and became the first considerable land area of a new 
western continent. 

Northward and southward we know little of the extent of this young 
continent. In the Fortieth Parallel area it stretched from the meridian of 
Battle Mountain eastward to the neighborhood of Wahsatch Range ; its west- 
ern border lifted in a general elevated region, while toward the east it grad- 
ually declined to the ocean level. Over the sea-bottom directly east of the 
eastern shore there was no disturbance whatever, as is shown by the abso- 
lutely conformable superposition of the Permian and Triassic beds on the un- 
disturbed Carboniferous floor. That it was higher along the west, is demon- 
strated by the enormous amount of Mesozoic sediment which was derived 
from its degradation. It was a land-mass with its extreme elevation and 


OROGRAPHY. 733 


extreme disturbance at the west, inclining gently to the east, and passing 
under the level of the sea, where its beds had never been disturbed. 

The Mesozoic oceans washed the shores of this continent, whose out- 
lines are as yet only partially traced. Southward from the region of Salt 
Lake City the distribution of Triassic rocks gives a clew to its shape, and 
shows that the eastern coast of the continent trended southwest. North- 
ward from Salt Lake the outline trended northward into Montana. From 
its western shore in the region of Battle Mountain the continental coast 
trended nearly due north and south. A very few years will suffice to 
indicate its full outline. From the passage westward of the Mesozoic rocks 
through Arizona and northern Mexico it is clear that this post-Carboniferous 
continent did not continue south and east of the system of the Colorado. 
It was the first nucleus of land in the West, newer than the then sunken 
Archzean Nevada land and the Archean island peaks of the Rocky Moun- 
tain region. 

On the five Analytical Geological Maps, Nos. VIII, IX., X., XL, and 
XII, accompanying this chapter, it will be seen that the ranges west of 
Salt Lake are given but three colors—post-Archzean, post-Jurassic, and 
Tertiary. The post-Carboniferous disturbances are not colored on the 
maps, for the reason that at present it is impossible to separate their actual 
orographical effects from the enormous system of folds which took place at 
the close of the Jurassic age. 


Post-Jurassic Orocrapuy.—Immediately upon the close of the Jura 
the sediments, which since the end of the Carboniferous had accumulated 
at the west of the new continent, were folded with an enormous develop- 
ment of horizontal compression, creating a belt of land lifted above the 
level of the sea for 200 miles out from the shore-line of the post-Carbon- 
iferous continent. The most elevated and most western of these post- 
Jurassic folds is the Sierra Nevada. East of that range the new addition 
to the continent, and the body of the post-Carboniferous continent as well, 
are now seen to be composed of a series of corrugated ridges, having north- 
east and northwest strikes. 

The folds of the post-Jurassic extension of the continent do not differ 


734 SYSTEMATIC GEOLOGY. 


in their mode of compression, in the character and magnitude of their anti- 
clinals, from those which succeed them to the east, and which are entirely 
composed of Palseozoic beds. It is impossible to decide on the present evi- 
dence whether the post-Carboniferous disturbance produced folded ridges, 
and the post-Jurassic added more to the west, or whether the post-Car- 
boniferous elevation was simply a plateau-like uplift, and all the foldings 
between the Wahsatch and the Sierra Nevada, including the latter range, 
were made in post-Jurassic time. When we realize that passing westerly 
from the Wahsatch region the folds grow more and more extensive and 
more and more complex, and betray greater and greater circumferential 
pressure, reaching a maximum in elevation and compression in the Sierra 
Nevada, it seems probable that the post-Carboniferous uplift simply defined 
an island without much crumpling, and that the whole Great Basin region 
received its corrugation at the close of the Jura. 

This view of the case is not without its difficulties. In the region 
of the Wahsatch, if the folding had been already post-Jurassic, we should 
naturally expect to find evidences of a discrepancy between the rocks dis- 
turbed at the close of the Jurassic and subsequent Cretaceous series ; 
but as far west as the Cretaceous extends, the two series are seen to be in 
general quite conformable. But it should be borne in mind that in the 
complicated sequence of disturbances which have occurred in the re- 
gion of the Wahsatch the actual shore of the Cretaceous ocean is not now 
seen; that the most western developments, viz., those along the eastern 
slope of the Wahsatch, are really well in the Cretaceous sea; and that 
the Cretaceous rocks certainly extended some miles west of their present 
termination. 

The strict and extended nonconformity which appears between the Cre- 
taceous and the Jurassic in California is not repeated on the eastern side of 
the land-mass. When we come, therefore, to consider the special orographi- 
cal structure of the ranges of the Great Basin between California and the 
Wahsatch, there is, counting from the west, a region extending from the 
Sierras out to the meridian of 117° 30’, in which the folded. strata are 
demonstrably of Triassic and Jurassic age, thrown into their positions by 
a period of compression at the close of the Jurassic. Between longitude 


OROGRAPHY. 730 


117° 30’ and the Wahsatch is a region which was lifted above the level of 
the sea at the close of the Carboniferous, but whose bold axes were very 
probably made contemporaneously with the western addition, at the close of 
the Jura. With this understanding I proceed to examine something of the 
detailed structure of this province of what have been called the Basin 
Ranges. 

These remarkable, quasi-parallel mountain bodies separated from each 
other by depressed valleys, which are occupied by fresh-water Tertiary 
and Quaternary beds, are a series of mountain islands lifted above desert 
plains. They have given rise to considerable discussion, and there 
is already some difference of opinion between Powell and Gilbert on 
the one hand and myself on the other. In Volume III. of this series, 
in a brief sketch of the Green River Basin, I alluded to the Basin Ranges 
as a series of folds.** Powell and Gilbert have called attention to the 
abundant evidence of local vertical faults and the resultant dislocation into 
blocks. One of the most common features of the Basin Ranges is a moun- 
tain body composed of a steeply or gently dipping monoclinal mass, edged 
on both sides by the horizontal desert formations, the back of the 
monoclinal mass consisting of inclined planes of strata, while the other 
face of the mountain body consists of an abrupt cliff, evidently the 
result of a vertical fault, which has been more or less modified by a com- 
paratively recent erosion. The frequency of these monoclinal detached 
blocks gives abundant warrant for the assertions of Powell and Gilbert that 
the region is one prominently characterized by vertical action; yet when 
we come to examine with greater detail the structure of the individual 
mountain ranges, it is seen that this vertical dislocation took place 
after the whole area was compressed into a great region of anticlinals 
with intermediate synclinals. In other words, it was a region of enormous 
and complicated folds, riven in later time by a vast series of vertical 
displacements, which have partly cleft the anticlinals down through 
their geological axes, and partly cut the old folds diagonally or perpen- 
dicularly to their axes. 


*Vol. IIL, page 45. ‘These low mountain chains which lie traced across the desert with a north- 
and-south trend are ordinarily the tops of folds whose deep synclinal valleys are filled with Tertiary 
and Quaternary detritus.” 


736 SYSTEMATIC GEOLOGY. 


Analytical Geological Maps X., XI, and XII, accompanying this 
chapter, show in three colors the main orographical features of the Basin 
region. The post-Archean, or, as they might more properly be called, 
pre-Cambrian folds, are indicated in brown; the main ridges of the 
Basin Ranges are shown as post-Jurassic, which is to be accepted with the 
qualifications already detailed; and the disturbed Tertiaries, both Eocene 
and Miocene, are ineluded within the yellow color. 

Leaving out of consideration now the Archean structure, I will call 
brief attention to the most interesting and characteristic details of the 
great folds of which all are supposed to be, and those west of longitude 
117° 30’ are known to be, post-Jurassic. 

Proceeding from the region of the Wahsatch westward, there is, first, 
the Oquirrh Mountains, whose topographical axis is north-and-south, but all 
whose geological lines of strike are northwest-southeast. The range, as will 
be seen at a glance by the lines of axis and arrows of dip, is composed of 
two parallel anticlinals with intermediate synclinal. The great northern 
synelinal, which is traced diagonally across the northern half of the Oquirrh 
group, when produced southward, is seen to lie through the middle of the 
Pelican Hills west of Utah Lake. The Oquirrh body, although inter- 
rupted by numerous small local faults, nowhere shows one of those deep, 
powerful dislocations which are characteristic of ranges farther west. 

Aqui Range and its northern extension, Stansbury Island, show a very 
peculiar curved anticlinal throughout the main mass of hills, but toward 
the southern extension only half the anticlinal is present, and a powerful 
fault-plane invades the axis. 

Promontory Range also shows a defined anticlinal, flanked both on 
the east and west by synclinals. 

An interesting instance of the complexity and obscurity of these 
ranges is shown by the Ombe Mountains. The southern extension of the 
range is a distinct anticlinal, having a northeast-southwest strike, its beds 
dipping from 15° to 17° on both sides. Northward this is succeeded by a 
parallel synclinal with far steeper dip, and still farther northward the entire 
range consists of a block of quartzites and limestones dipping altogether 
to the west, with a tremendous fault-face exposed to the east, where a 


OROGRAPHY. fou 


sharp escarpment displays six or seven thousand feet of the edges of the 
ruptured beds. 

Gosiute Range next west is essentially a single anticlinal, which has 
been tremendously distorted and thrown into horizontal curvature by longi- 
tudinal compression of the ridge. The northern and southern portions 
show distinct anticlinals, but a wide middle region is composed of a single 
monoclinal ridge, which is the westerly dipping half of the anticlinal. An 
explorer passing over this middle part might easily suppose the range to be 
a single monoclinal rock-mass dislocated from its geological connections, 
but at the points indicated on the map the true anticlinals make their 
appearance. 

The adjoining Peoquop Range shows throughout its long north-and- 
south member a monoclinal structure, being composed entirely of beds 
dipping to the west, but in the southern portion these beds are seen to pass 
under a distinct synclinal, and then west of the depression to rise and 
pass over a well defined anticlinal in the region of Antelope Buttes. The 
northern part of Egan Range also shows a true anticlinal, which is 
obviously the southern continuance of the Antelope Butte anticlinal; but 
in passing southward the Egan Range axis passes out of the mountain 
group, and the whole southern portion is a monoclinal ridge, being a relic 
of the westward dipping part of the anticlinal. Here, again, an explorer 
visiting only the different ends of the range would gain a totally false view 
of its general structure. It is truly an anticlinal, having a northwest-south- 
east strike, which in the southern portion has been cut by a meridional 
fault, the entire eastern half of the anticlinal having been dislocated down- 
ward out of sight. It is thus never safe to generalize as to the structure of 
one of these ranges from an interval of forty or fifty miles of its dips. 

A very false conception would also be arrived at whenever geological 
examination was confined to one of the single detached bodies. Egan 
Range, Antelope Buttes, the Cedar Mountains, and a part of Tucubits 
Range are all portions of one anticlinal fold of sinuous strike. At the 
northern end of Egan Range the northwest anticlinal axis has curved 
to a slightly northeast position, which strike is taken up in Antelope 
Buttes, and there describes a double curve, ending near Eagle Lake with a 

47 K 


738 SYSTEMATIC GEOLOGY. 


northwest strike. The same axis recurs directly north in the Cedar Moun- 
tain group, and describes a broad curve with its convexity to the west, 
finally reaching a northeast trend. Relics of the synclinal axis which lie 
along the east side of this prolonged anticlinal are to be seen in the lower 
portion of Peoquop Range, directly east of Antelope Buttes, where there 
is a distinct downward curve of the continuous strata, which rise again into 
the great monoclinal range of Peoquop. The same synclinal recurs between 
the northern end of Peoquop and the Cedar Mountains. West of this long 
anticlinal another companion synclinal is to be traced in the Ruby group, 
and again in the depression between Euclid Peak and the Tucubits Moun- 
tains. Here, then, we are able to trace a single anticlinal, with but slight 
local breaks where the Quaternary valley deposit sweeps over the low passes 
of the axis, with synclinals both to the east and west shown at several char- 
acteristic points. In the case of the Egan group the entire fold has been 
abruptly cut off by a fault in the latitude of Gosiute Peak, the fissure having 
a trend slightly east of north. ‘Nowhere in this long interrupted anticlinal 
are the geological exposures deep enough to lay bare the Archzean rocks. 

The main mass of Humboldt Range is made up of a central core of 
Archean schists and granites, from which on either side dip away the 
flanking Palzeozoic bodies of a great anticlinal fold. The Humboldt was 
one of the greater Archean ranges, and the subsequent Palseozoic rocks 
are deposited unconformably, abutting against its steeply inclined flanks, 
leaving unsubmerged insular Archzean summits. The modern axis of fold 
is not laid down on Analytical Map XI., but the Paleozoic bodies are seen 
on either side dipping away from it, the greater body in the latitude of 
Ruby Valley inclining about 15°, and the fragments of the westerly dipping 
mass which appear along the northern portion of the range decliniag at 
angles from 20° to 25°. Where the southern Palzeozoic body terminates 
northward, between Ruby and Franklin lakes, the edges of its bed approach 
the region of a great fault, in the neighborhood of which they are turned 
up into a vertical position. From that point northward as far as Eagle 
Lake the eastern face of the mountain fold is the result of a powerful fault, 
the dislocated eastern half of the fold having sunk out of sight. 

The next system of folds is developed in Pinon, Elko, and River 


OROGRAPHY. 739 


ranges. The central portion of the Pinon is formed of an anticlinal, dis- 
playing a magnificent arch of Cambrian, Silurian, and Devonian strata. 
This axis, although in general meridional, describes a broad curve with a 
convexity to the west. At its southern termination it is cut by a trans- 
verse fault of northeast-southwest trend, and the further southward con- 
tinuation of the fold of rocks disappears by subsidence. The same power- 
ful northeast-southwest break has cut off the end of the lofty Diamond 
Mountain range which enters the map from the south and occupies the 
region between the lower end of the Humboldt Mountains and the southern 
portion of the Pinon. This is a great anticlinal, composed of Carboniferous 
and Devonian strata, which is possibly the southward continuance of the 
curved fold of the Pifion, its beds having been horizontally dislocated and 
thrown to the northeast. The main Pifon axis near latitude 40° 30’ is 
again severed by a powerful northwest-southeast fault and its further con- 
tinuance lost, the dislocated northern portion of the range having gone 
down and its summit become covered with great outflows of volcanic rocks. 
North of the Humboldt the same axis continues in River Range, but 
its appearance as an anticlinal is only for a very short distance. ‘There 
again the axis is cut, this time not across its trend, but by a longitudinal 
fault which has cleft the heart of the fold, the entire eastern half for forty 
miles having been dropped out of sight. 

The little Elko group of mountains south of the Humboldt is shown 
as a body dipping to the southeast with a northeast strike. This is evi- 
dently no part of a regular fold, but is a simple monoclinal block dislocated 
upward from the easterly dipping half of the main anticlinal. In River 
Range, north of Penn Canon, where the mountain group considerably 
widens, the fault which has divided the axis up to that point passes out on 
the east side of the range and a relic of the complete anticlinal is left, a 
small portion of the easterly dipping beds appearing distinctly on the eastern 
face of the range, while the main body is composed of the westerly dipping 
member. Passing still farther north, this westerly dipping member develops 
a defined synclinal and again reappears with an eastern dip at the northern 
extremity of the range. The main anticlinal is therefore traceable for a 
hundred miles, although cut by longitudinal, diagonal, and transverse faults. 


740 SYSTEMATIC GEOLOGY. 


The synclinal which accompanies it on the west appears north of Penn 
Canon at the point indicated, and again in the region of Pinon Pass, where 
a distinct downward curve of the Devonian beds is developed. South and 
west of the latter point the beds again rise with an easterly dip and develop 
the eastern part of the anticlinal, whose westward member is again cut off 
by a longitudinal fault and displaced downward. Besides the dislocations 
mentioned, it will be seen that the general strike is remarkably sinuous, 
passing from a northeast to a southeast direction. The general axis, contin- 
uing from the Diamond group through the Pinon into River Range, makes a 
single great curvature with a convexity to the west, approximately parallel 
to the great curved strike developed in Humboldt Range. 

West of the Pinon group the whole country for some distance is deeply 
shattered and cleft into great mountain blocks, many of which relatively 
to the others have gone down, leaving only a few isolated high points of 
stratified rocks. It is impossible in these to make any connected system 
of strike. At Nannie’s Peak in Seetoya Range, around a central nucleal 
mass of Archzean rocks there is an interesting oval quaquaversal. 

In the Cortez, which is almost altogether covered and masked by vol- 
canic outbursts, two distinct axes are developed—one a limited synclinal 
between Cortez and Tenabo Peaks, the other a fragmentary anticlinal in 
the region of Dalton Peak. 

On Map XII. the eastern portion, including Battle Mountain, and Sho- 
shone and Toyabe ranges, shows singularly discordant axial lines. The 
Toyabe is a distinct anticlinal approaching the meridian, but it does not 
continue northward, and a little south of latitude 40° is cut off by an 
east-and-west fault, the further continuation being lost. Shoshone Range 
develops an exceedingly slight exposure of an anticlinal in the region 
of Ravenswood Peak, which is entirely surrounded and its continuation 
masked by floods of rhyolite. The main mass of Shoshone Range north 
of Reese River Canon consists of the easterly dipping continuation of this 
Ravenswood anticlinal, the western half appearing in Battle Mouniain. 
These two enormous masses of quartzitic beds represent the eastern and 
western half of the anticlinal whose axial summit is exposed at Ravens- 
wood, the prolonged axis lying deeply buried beneath the valley of Reese 


OROGRAPHY. 741 


River. It is evident that a tremendous series of faults and subsidences 
has depressed the main part of this great fold, the sunken member being 
covered by the Quaternary and Tertiary of the Reese River valley and 
the great rhyolitic flood. 

West of this fold, as seen upon Map XIL, there are but three consid- 
erable bodies of stratified rock. They are Havallah, Pah-Ute, and West 
Humboldt ranges. Little fragments of sedimentary rocks, it is true, 
appear here and there in points of deepest erosion of the great rhyolitic 
field, as in the Desatoya Mountains and the southern part of the Augusta 
group. The first body of importance is the Havallah, which is a distinct 
anticlinal formed of Alpine Trias strata. The general trend of the main 
part of the anticlinal is northwest, but in the Signal Peak ridge the axis 
deflects around a curve and passes into a northeast direction. A minor and 
altogether subordinate synclinal appears parallel to the main axis and to 
the west of it. After the axis has passed into its northeast trend it en- 
counters a powerful fault, by which its continuance is cut off and dropped. 
The companion synclinal of this fold appears in the canon between Iron 
Point and Golconda. 

The structure of Pah-Ute Range is rendered even more obscure by 
faults and dislocations. The anticlinal which is the foundation of the sys- 
tem appears at the northern point of the range in the region of Dun Glen 
Peak, and is observable southward nearly to the latitude of 40° 30’. Only 
a small portion of the easterly dipping beds are seen, and they are soon cut 
out by a longitudinal fault which cleaves down the heart of the ridge as far 
south as Granite Mountain, where the easterly dipping beds have totally dis- 
appeared. From Granite Mountain the axis is deflected into a sharp south- 
westerly curve, and another system of faults has, from that point to the 
southern termination of the range, cut off the westerly dipping member. 
North of Granite Mountain the main bulk is composed of the westerly 
dipping half of the fold, and south of Granite Mountain altogether of the 
easterly dipping member. At the extreme western base of Granite Moun- 
tain, cropping through the Quaternary valley deposits, are the summits of 
the sunken body of the westerly dipping part of the anticlinal, which have 
been faulted down. 


742 SYSTEMATIC GEOLOGY. 


West Humboldt Range repeats the same peculiar and interesting 
condition. The main anticlinal axis is developed from the region of 
Sacramento Canon diagonally across the topographical axis of the range. 
Near the mouth of Sacramento Canon a northwest-southeast fault has 
oceurred, with a powerful horizontal displacement, by which the axis is 
faulted about five miles. From the region of Buffalo Peak northward 
nearly to Humboldt River a meridional fault has occurred, cutting diag- 
onally across the geological axis, dropping its northward continuation out 
of sight, and giving to the topographical form of the mountain body a north- 
and-south trend, which is at an angle of 30° with the geological strike. West 
of the West Humboldt the exposures of the sedimentary rocks are of so 
limited an area, and their geological relations and continuations are so 
masked by floods of voleanic rocks, that it is unprofitable to pursue their 
details further. 

While this brief description, from the complicated nature of the facts, 
may fail to convey a full idea of the state of things on the Basin Ranges, 
yet a careful scrutiny of the axis-lines, as laid down upon Analytical Maps 
X., XL, and XII, will show: a. that the region is one displaying a continuous 
series of folds of Paleeozoic and Mesozoic rocks; 0. that the general trends of 
these axes approach more nearly a meridian than an east-and-west line; 
c. that the axes themselves often display broad general curves traced through 
a hundred miles, their grander convexities being turned to the west; d. that 
in detail the axes are further subject to minor sinuosities obviously due to 
longitudinal compression; and, e. that the whole region has been most 
irregularly invaded by a series of faults which are east-and-west, north-and- 
south, northeast-southwest, and northwest-southeast. The result of this 
complicated interlacing system of dislocation is, that all the ranges of the 
Great Basin are broken into irregular blocks, sections of which have sunk 
many thousand feet below the level of the adjoining members. It frequently 
happens that anticlinal or synclinal axes have been the loci of the fissure- 
planes, and that in the accompanying dislocations halves of folds are left in 
long, well defined monoclinal ridges. When a fold is cut, either diagonally 
or transversely, by a fault, there is not infrequently a considerable horizontal 
displacement, as may be seen in the case of the West Humboldt, where the 


OROGRAPHY. 743 


anticlinal axis is displaced five miles horizontally, and in the case of Pinon 
Range, where there is a still greater lateral movement. 

That these faults were not contemporaneous with the great folding 
period, is obvious from their relations to the axis. Parallel faults often cut 
transversely or diagonally across a completed fold, dislocating anticlinal 
blocks which could never have been formed if the faults were contempora- 
necus with the folding. When we remember that the Eocene and Miocene 
Tertiary rocks which have been laid down within the hollows of these 
post-Jurassi¢ folds, have themselves been thrown into waves and inclined 
positions up to 40°, and that these Tertiary beds are often violently 
faulted, it is evident that in extremely modern geological history there 
has been sufficient dynamic action to account for the system of faults. 
Furthermore, the enormous volume of volcanic products which is directly 
related to the subsided, dislocated blocks would seem to indicate that much 
of the faulting took place within the Tertiary age. 

Whether we consider the country in lines transverse to the main axes 
of flexure, or parallel with those axes, it is evident that horizontal com- 
pression or actual diminution of area has occurred. 

Tracing one of the great curved anticlinals like that of the Pinon, or 
that of Egan-Peoquop Range, with its northward continuation, and counting 
in the diminution of length of fold due to longitudinal compression, it will 
appear that there is not less than ten or fifteen per cent. of actual con- 
traction. This law of longitudinal compression, so ably brought out by 
my colleague, Mr. 8. F. Emmons, in his account of Toyabe Range, in 
Volume III. of this series, is a rule which holds in every single range of the 
Great Basin we visited. 

When the country to the south and north of the Fortieth Parallel area 
comes to be carefully examined geologically, it will no doubt be possible to 
connect the main geological axes over the whole Great Basin, and to show 
with entire precision both the longitudinal and the lateral contraction which 
the surface of the region has suffered. From what I have seen in the 
Fortieth Parallel field, I am confident. that the whole area has suffered a 
linear diminution of ten per cent. It is evident from the sections, also, that 
all or nearly all of the diminution of area or compression of surface took 


744 SYSTEMATIC GEOLOGY. 


place at the time of folding. In the phenomena of the dislocated blocks 
which are the result of the great system of vertical faults, there is no 
evidence whatever of contraction of surface. Wherever we get a clew to 
those faults they are long continued planes of dislocation, often 60 to 100 
miles in length, approximately vertical, and in the phenomena of irregular 
subsidence which has resulted from their action there is absolutely no 
proof of contraction. 

The geological province of the Great Basin, therefore, is one which 
has suffered two different types of dynamic action: one, in which the chief 
factor evidently was tangential compression, which resulted in contraction 
and plication, presumably in post-Jurassic time; the other of strictly ver- 
tical action, presumably within the Tertiary, in which there are few evi- 
dences or traces of tangential compression. 

The two grandest fault-lines shown in the Great Basin are those 
which define its east and west walls. Whoever has followed the eastern 
slope of the Sierra Nevada from the region of Honey Lake to Owen’s 
Valley cannot have failed to observe with wonder the 300 miles of 
abrupt wall which the Sierra Nevada turns to the east. That wall is no 
other than a great continuous fault by which the Nevada country has 
been dropped from 3,000 to 10,000 feet downward. In this low trough 
east of the Sierra Nevada and Cascade Range is laid down the thick 
series (amounting to 4,000 feet, as already described) of Miocene beds. It 
is therefore evident that this was a depression which was defined before 
the beginning of Miocene time. On the western base of the Sierra Nevada, 
the marine Miocenes are found far down abutting against the extreme foot 
hills of the range. As yet in the depressed area east of the Sierra Nevada 
no Eocene beds have been discovered, from which it seems highly prob- 
able that the great fault occurred either within the Eocene or at the close 
of Kocene time, and was the direct cause of the subsidence whose area was 
immediately occupied by the Miocene Pah-Ute lake. 

Since the Sierra Nevada along its crest and eastern wall is chiefly 
formed of granitoid rocks, it is impossible to determine the amount 
of the drop which the downward movement has caused; for if, as is 


evident, the fault occurred before the Miocene, there has been the enor- 


OROGRAPHY. 745 


mous erosion of all subsequent time to reduce the crest of the great 
range. 

In the case of the long Wahsatch fault we have a line of dislocation 
traced across the entire breadth of the Fortieth Parallel belt of 100 miles 
from north to south. As to the date of this fault, we are somewhat in 
the dark. The present Wahsatch Range, let it be remembered, was up- 
‘heaved at the close of the Cretaceous, and during the Vermilion Creek 
period of the Eocene the country directly to the west of the Wahsatch 
was a high land whose abundant detritus was swept down into the Hocene 
lake. At the close of the Vermilion Creek period this region suffered 
a sudden and remarkable depression, which permitted the waters of the 
Eocene lake to flow westward over what had been high lands as far as the 
middle of Nevada, as shown by the middle Eocene strata extending to Elko. 
It seems, therefore, not improbable that the great Wahsatch fault occurred 
with that subsidence of central Utah which we may place at the close of 
the lower Eocene epoch and prior to that of Green River. If the Sierra 
Nevada fault was contemporaneous, it is not a little curious that we have 
failed to find any fresh-water Eocene beds in the depression east of the 
great range, either in Oregon, Idaho, or California. The country is so 
masked by voleanic rocks, and there are such enormous deposits of Quater- 
nary, that they may yet exist without our having detected them; and it is 
not impossible that evidence will be found of the synchronism of the two 
great faults. 

Fortunately, in the case of the Wahsatch fault we have, in the Cotton- 
wood region of the Wahsatch, a magnificent exposure of folded stratified 
rocks through which the plane has cut, and from the direct, evident read- 
ing of the section it is clear that the fissure which traced itself throughout 
the axis of fold of the Wahsatch in this particular neighborhood caused the 
westward member to sink fully 40,000 feet. A relic of the eastern half of 
the great arch of Paleozoic and Mesozoic rocks still remains in position, 
its summit members deeply worn away by post-Cretaceous erosion, but 
all the details of the sequence of rocks are so clear and so perfectly ex- 
posed that there can be no doubt of the quantitative correctness of my read- 


ing of this tremendous dislocation. In passing northward we have less 


746 SYSTEMATIC GEOLOGY. 


direct evidence of the amount of the fault, but through the northern part 
of the range it cannot have dropped less than two miles. The action is 
simply a vertical one by which the western half of the Wahsatch and the 
country lying west for some miles was, relatively to the eastern part of the 
range, dropped, and the dislocation took place on the axial line which cut 
the region of the extreme topographical heights of the Cottonwood group, 
where the maximum downfall was, as announced, 40,000 feet. 

It is interesting to recall here that this region of the great Wahsatch 
fault had also been a theatre of enormous dislocation in the Archzan age, 
for the most remarkable single feature of pre-Cambrian topographical devel- 
opment in the Fortieth Parallel area is the great Archeean fault-face against 
which the Palaeozoic members were made to abut in the process of deposi- 
tion, and, as has already been seen in the discussion of the Pliocene, the 
same line of weakness yielded to a strain at the close of the Pliocene, by 
which the valley of Salt Lake suffered a depression of over 1,000 feet. G. 
K. Gilbert shows further subsidence along this line during the Bonneville 
period, and announces post-glacial activity on this historic line of weakness. 
It is evident, therefore, that this remarkable topographical feature of the 
great steep wall of Wahsatch Range has been from the earliest geological 
history a plane of recurrent displacement. 

We are not surprised when an underlying Archean ridge is found 
to be the determining cause of a modern range, but it is extremely striking 
to find a line of actual dislocation maintaining itself throughout such an 
enormous length of geological time. 

If I am right in placing the Wahsatch fault at the close of the Vermil- 
ion Creek epoch of the Eocene, it is further of the greatest interest that 
the country which went down was the country which had been elevated to 
the most extreme heights, and which had furnished the enormous sediments 
of Vermilion Creek Lake. Here is a repetition of the law illustrated in the 
great displacement at the close of the Carboniferous already described in 
western Nevada, according to which a region of extreme elevation that 
had been enormously eroded immediately thereafter suffered paroxysmal 
depression. 


Post-Creraceous OrocrapHy.—The same difficulties which attend the 


OROGRAPHY. 747 


separation of the effects of post-Carboniferous and post-Jurassic disturbance 
in western Nevada, accompany the attempt to disentangle the action of the 
post-Cretaceous from the earlier disturbances in the region of the Wahsatch. 
It is clearly seen from the conformity of the series that the great fold of the 
Wahsatch occurred at the close of the Cretaceous. It is also evident from 
the non-continuance of all the Mesozoic rocks west of Salt Lake, and the 
total difference of the eastern Mesozoic series from this development in 
western Nevada, that the continental mass raised at the close of the Car- 
boniferous intervened between the western Nevada Mesozoic region and 
that east of and including the Wahsatch. The non-continuance of the 
Mesozoics west of the Wahsatch and the remarkable sedimental change 
between the Upper Coal Measure limestone beds and the purely detrital 
rocks of the Triassic would indicate a considerable change of level con- 
nected with the post-Carboniferous upheaval in the region of the Wahsatch. 
It must be remembered that the actual shore of the post-Carboniferous 
upheaval of land was a little west of the present Wahsatch. 

The conformity of the Trias, Permian, and Upper Coal Measures in the 
Wahsatch is proof that, whatever may have been the character of the topog- 
raphy of the shore, no orographical disturbance touched the area of Mesozoic 
deposition. It was this absence of all plication in the Carboniferous sea- 
bottom, up to the very edge of the post-Carboniferous continent, together 
with the paucity of Triassic sediments, as compared with those west of the 
Mesozoic land area, that led me to infer for the character of the land in the 
Wahsatch or east shore region a low, unfolded surface lifted gently from 
the mediterranean ocean, where, as we know, the Carboniferous beds lay 
undisturbed. 

Whether the post-Jurassic system of folds which threw up the great 
ranges of western Nevada, including the Sierra Nevada, continued its action 
as far east as the Wahsatch, it is impossible to tell. 

At the close of the Cretaceous the Wahsatch itself was uplifted, and 
the country as far east as the Mississippi Valley felt the effect of the great 
dynamic impulse. As far as the evidence within the Fortieth Parallel area 
goes, the action of the post-Cretaceous uplift is simple in its general effect. 


The close of the Cretaceous found a continuous sea from the base of the 


748 SYSTEMATIC GEOLOGY. 


Wahsatch to the region of the Mississippi Valley. It was that mediter- 
ranean ocean whose outlines were defined by the post-Carboniferous uplift. 
It is clear that in the late Carboniferous an uninterrupted ocean at times 
extended from the Archzean shore in western Nevada to the Appalachian 
Range. The main effect of the post-Carboniferous upheaval was to lift 
two land-masses, one east of the Mississippi and one west of the Wahsatch, 
leaving the intermediate mediterranean sea. 'The great effect of the post- 
Cretaceous upheaval was to lift the bed of that mediterranean sea com- 
pletely above the marine plain, thus uniting the two separated parts of 
America and making it a single continent. The effect of post-Cretaceous 
action in the immediate Fortieth Parallel region was, first, the development 
of a broad level region, now occupied by the system of the Great Plains; 
secondly, the outlining of the basin of the Vermilion Creek Eocene lake; 
thirdly, the formation of distinct folds, of which the Wahsatch and Uinta 
are the most powerful examples; fourthly, the relative upheaval of the old 
Archzean ranges, whose highest points had through all geological time since 
Archzean ages existed as island-points lifted above the marine plain. 

The system of the Rocky Mountains, composed here of its three 
subordinate ranges, was, as regards the bottom of the Eocene lake basin, 
generally elevated. The lake basin itself was thrown into a series of broad, 
gentle folds and local quaquaversals, determined by underlying Archean 
bodies, and its area was prominently divided by the great east-and-west 
Uinta fold. <A correct idea of the magnitude of the grander post-Cretaceous 
folds may be gathered from the sections of the Wahsatch and Uinta. The 
fold of the Wahsatch involved a conformable series from the base of the 
Cambrian to the summit of the Cretaceous, in all about 44,000 feet, and 
from the present position of the rocks it is clear that a full section of the 
fold was above the present level of Salt Lake; so that, since the ocean 
level was banished to somewhere near its present position, the fold itself 
was not less than 44,000 feet in altitude. The Uinta was not so imposing 
a body, but its summit before erosion began was certainly 30,000 feet above 
the sea-level. 

Relatively to the surrounding country all Archean ranges within the 


area involved were lifted, co that the Cretaceous strata which overlay their 


OROGRAPHY. T49 


passes and the rocks which abutted against their mountainous flanks were 
thrown either into continuous arches over the depressed parts of the Archeean 
ranges or into inclined belts along their flanks. 

Before the commencement of the post-Cretaceous erosion, and before 
the basin of Colorado River began to be covered by the fresh-water 
lake of the Vermilion Creek Eocene period, the general topography, the 
result of the post-Cretaceous fold, was that of enormous arches which were 
locally broken and dislocated into irregular blocks, and these folds were 
separated from each other by wide areas of gentle undulation or entire 
horizontality. One of the most interesting features in the whole orograph- 
ical phenomena of America is the development of broad inclined planes 
south of the Fortieth Parallel work, in what is known as the Colorado Pla- 
teau. Here are areas which have been and are being ably described by 
Messrs. Powell and Gilbert, in which the sea-bed becomes an undisturbed 
plateau 5,000 and 6,000 feet above the level of the subsequent ocean. 
When we come to examine the relations of the post-Cretaceous folds with 
these adjacent undisturbed plateaus, it is evident that there were large 
regions in which no superficial contraction or diminution of area took place, 
whereas there were others in which occurred the most enormous and com- 
plex plications. Any theory, therefore, which attempts to account for the 
-superficial results of geological dynamics will have to account for the exist- 
ence of wide regions which, relatively to the sea, are suddenly upheaved 
without the slightest contraction, plication, fold, or fault, and of other 
regions within the same stratigraphical province which suffered the most 
extreme local compression, and all the complexities which can ensue from 
fold and fault. 

When we study critically the underlying geology in connection with 
each of the great folds, it is evident that wherever an Archean mountain 
range underlay the subsequent sheets of sediment, there a true fold has 
taken place. If the reader will look at the sheet of sections in the General 
Atlas, he will see that the old Archean ranges of Rocky Mountains are 
flanked upon each side by conformable Palaeozoic and Mesozoic beds dip- 
ping away from the Archean bodies. For example, on a line drawn 
northwest-and-southeast across the end of Park Range, Medicine Bow, 


750 SYSTEMATIC GEOLOGY. 


Laramie Plains, and Colorado Range, the three Archean bodies form the 
loci of three distinct uplifts, the later sedimentary beds being thrown into 
inclined positions. When we observe the continuity of the strata across 
such a valley as that of Laramie Plains, and then see them sharply and 
suddenly rise against the foot-hills of the Archean, it becomes evident that 
the entire area of the Rocky Mountains has suffered actual lateral com- 
pression, and that the diminution of surface amounts to from six to ten per 
cent. When we further consider that the post-Archzan sedimentary rocks 
must be regarded as a mere thin covering over the solid subjacent crust, 
this diminution of area of actual surface means an actual compression of 
the solid Archzean shell of the earth. 

In the case of the Wahsatch it is seen from the relations of the old 
Archzan underlying range that that enormous mountain body determined 
the existence and character of the post-Cretaceous fold. In the case of the 
Uinta it is impossible to say how far underlying Archean rocks have 
played a part. The single limited outcrop of pre-Cambrian rocks at Red 
Creek, however, is certainly at the most ruptured and actively dislocated 
point of the whole Uinta Range. 

The entire thickness of conformable rocks from the Cambrian to the 
top of the Cretaceous does not amount in the region of the Laramie Hills 
to more than 5,000, or at the most 6,000, feet. East of Colorado Range 
stretches the uninterrupted Great Plains. With this shallow covering of 
rock the non-protrusion of Archzean peaks over the surface of the Plains 
is ample proof that no hills of considerable height existed at the close of 
Archean time over that whole area. The Archean rocks of Missouri are 
the first of the series to the east that rise above the limit of the later sedimen- 
tary beds. In other words, a region that was not a region of Archean 
mountains in the great orographical period which lifted the whole of that 
country above the level of the sea, suffered neither plication, nor fault, 
nor local disturbance. It is also noticeable that much of the great undis- 
turbed Colorado plateau shows only low Archzean forms underlying its 
sedimentary series, and those, although plainly eroded into hills, as de- 
scribed by Newberry, Powell, and Gilbert, are never accidented into con- 
siderable mountain chains, the law evidently being, that over what was 


OROGRAPHY. 751 


comparatively flat Archaean country the subsequent orographical move- 
ment has the effect of wide-spread bodily upheaval without local disturb- 
ance. This law, which is carried out so distinctly and so powerfully over 
the Cordilleras, is again shown in the Mississippi region, where a compara- 
tively thin coating of sedimentary beds lies on a generally smooth under- 
lying Archean territory, and the result is no considerable fold; but where, 
in the Appalachian chain, we again arrive at a system of old- Archean 
mountains, they have again in post-Carboniferous time determined the pro- 
duction of great modern ranges. From these relations of pre-Cambrian 
and more modern topography, it seems to be a general law that the config- 
uration of America is almost wholly due to the topography of the primeval 
pre-Cambrian continent. The power of underlying ranges to determine 
the position of modern uplifts is not confined to those lofty ridges whose 
summits were lifted as islands above the plane of later deposition, but is 
equally shown in the case of ranges whose summits were deeply submerged. 
It is demonstrable that the highest of the Archzean Wahsatch ridges were 
covered by at least 10,000 feet of sediment, yet in the post-Cretaceous 
fold the more modern rocks were thrown into a distinct enormous arch 
over the previously defined Archzean ridge; and in the case of the Laramie 
Hills, which were covered by from three to five thousand feet of horizontal 
sediment, the post-Archzean sediments were thrown into an anticlinal over 
the top of the Archzean body. 

In connection with these post-Cretaceous folds over the Archean 
bodies are some very interesting effects of compression and distortion of the 
central Archzean mass. Fortunately, in the case of those Archean points 
which were sufliciently raised to continue as islands during the whole of 
the Cretaceous, we have, from the accidents of modern erosion, an exhibi- 
tion of the planes of contact between the old Archean and a variety of 
horizons of the Cretaceous. Along the shores of these islands, making all 
allowance for variation in depth of the waters, it seems probable that a 
given horizon of the Cretaceous represents something like an old horizon- 
tal shore-plane. In the present condition it is interesting to observe how 
this once horizontal plane has been thrown into vertical sags. From 
the modern positions of these old shore-lines it is seen that the Archaean 


(a2 SYSTEMATIC GEOLOGY. 


body suffered in the post-Cretaceous orography not only an irregular uplift 
resulting in vertical waves, but a true torsion by which the body of the 
island has actually yielded to a twisting force amounting in some places 
to a shear of 5,000 feet. Wherever an Archean ridge was flanked by 
horizontal abutting strata, and these strata were afterward thrown into a 
position inclined to each other, it is evident that the interval of Archzean 
rock must have been compressed, and in yielding to this force the 
Archzean bodies have developed an amount of plasticity which, in view of 
their crystalline nature, is very surprising. 

The writer has observed that slabs of marble when supported by their 
ends sag in the middle, taking a permanent set. Similar observations have 
not to my knowledge been made on granite, but it is evident from the 
modern stratigraphical relations of these Archzan islands and Archzan 
ridges that they have suffered a shear and taken a permanent set, with a 
surprising development of plasticity. 

Among the more interesting detailed features of the post-Cretaceous 
uplift in the Rocky Mountains are the following: All the Laramie hills 
north of the 41st parallel were clearly overarched by a continuous anti- 
clinal fold of the conformable series from the Cambrian to the close of the 
Cretaceous. A little south of the 41st parallel the Archean heart of the 
range rises, there forming the great island which continued for many 
miles to the south. North of that point the post-Cretaceous erosion has 
removed the whole top of the anticlinal arch, leaving only a narrow band 
of sedimentary rocks margining the east and west flanks of the Archean 
central ridge. 

Throughout the hundred miles of easterly dipping sedimentary beds 
along Colorado Range exposed within the Fortieth Parallel area, the nar- 
row foot-hill zone dipped always from the Archzan nucleus, varying at 
angles from 16° to 80°. This belt of inclined rocks is very narrow, 
usually comprised within a width of four miles. Passing eastward it sud- 
denly flattens to the horizontal and extends in that position out upon 
the Plains. This angle of flexure is always visible where not masked by 
the subsequent Tertiary rocks. The character of the bend is extremely 
sudden, and the superficial exhibition is usually within the limits of the 


OROGRAPHY. 753 


Colorado Cretaceous clays, the overlying sandstones having been worn off 
from the immediate top of the curve. 

An interesting feature of this foot-hill region is the manner in which 
the narrow band of inclined sedimentary beds follows all the minor sinu- 
osities of the Archean topography. This is clearly shown on Big Thomp- 
son Creek and the Chugwater Promontory. 

The Laramie Plains form a horizontal area of Cretaceous, lying like a 
bay in the angle of Medicine Bow and Colorado ranges. This undisturbed 
plain of Cretaceous, in approaching the two mountain ranges, rapidly bends 
up to dip-angles of from 2° to 30°. 

In the broad Cretaceous exposures between the 106th meridian and 
that of 107° 30’, Analytical Geological Map VIII. shows an interesting 
combination of anticlinal and synclinal axes. At Rawlings Peak occurs 
the oft-mentioned quaquaversal ridge, the longer axis striking northwest- 
southeast, being evidently the continuation of Park Range. 

Decidedly the greatest of the features of the Cretaceous uplift are 
Uinta and Wahsatch ranges. The Uinta, especially, forms a type of oro- 
graphical structure elsewhere very uncommon. It consists of a broad cen- 
tral plateau, a hundred and fifty miles long by thirty miles wide, in which 
there are slight sags and local undulations, but the average dip of the strata 
is from the horizontal only up to 4° or 5°. This broad flat-topped arch 
suddenly gives way along the north and south edges to two distinct axes 
of flexure, where the horizontal rocks bend over, accompanied by distinct 
faulting, and dip from the northern axis north, and trom the southern axis 
south, at angles varying from 10° to 70°. In the region of Green River 
Canon the southern line of flexure becomes immensely complicated, and de- 
velops three local anticlinals. A glance at Analytical Geological Maps IX. 
and X. shows the position and average dip of angles along the northern and 
southern axial lines. 

In the Wahsatch the most remarkable features are, first, the develop- 
ment of a curved strike around a nucleal mass of granite in the Cotton- 
wood region, where the rocks describe the complicated bends shown by 
the detted line of the geological axis. Although partially covered with 
Tertiary strata, the next northern exposure of Archzean rocks—that near 

45 K 


754 SYSTEMATIC GEOLOGY. 


the 41st parallel—is again surrounded by a semicircular zone of inclined 
rocks which dip away from the nucleus in every direction. The northern 
end of the Wahsatch develops a very singular complexity. The easterly 
dipping rocks of the immediate mountain flank, besides suffering longitu- 
dinal fault, which partially duplicates the series, pass under a broad 
synclinal and rise again over a prominent anticlinal in the region of the 
meridian of 111° 30’, 

All the post-Cretaceous folds are more or less dislocated into detached 
blocks. A part of this action, as in Ogden Ridge, was a feature of the original 
uplift, but others, as the Great Wahsatch fault, were long after the creation 


of the fold. 


Tertiary Orocrapny.—From the close of the Carboniferous the 
region immediately west of the Walisatch had been the shore of the Meso- 
zoic ocean. After the post-Cretaceous folding of the Wahsatch and Uinta 
there is no reason to suppose that the old continental mass followed the law 
of paroxysmal subsidence of lightened areas. We arrive at the knowledge 
that the old post-Carboniferous land remained relatively superior to the 
newly folded country, including the Wahsatch and the country east of it, 
from the fact that the Vermilion Creek (Ute) lake formed in the basin directly . 
east of the Wahsatch, and its beds overtopped the lower portion of that 
range and continued a little farther westward, abutting against a highland. 
This highland, which at first was certainly in places more than 40,000 feet 
above the sea-level, suffered the rapid and intense erosion which pro- 
duced the 5,000 feet of Vermilion Creek sediments. That series, during 
deposition, was a subsiding series, as is evident by the successive shore 
conglomerates which recur along the western development of the group at 
intervals through the whole 5,000 feet of thickness. At the close of the 
Vermilion Creek age a new orographical period ensued, whose effects are 
only chronicled in the area of the Fortieth Parallel between the Rocky 
Mountains and Havallah Range. The Vermilion Creek rocks are thickest 
next to Wahsatch and Uinta ranges, which formed their chief source 
of supply, and thinnest farther east, where the edges of their beds over- 


lap the nearly horizontal Cretaceous toward the Rocky Mountains ; 


OROGRAPHY. 755 


and in the post-Vermilion Creek orographical epoch, the eastern part of the 
basin, where the beds were thinnest, was left undisturbed. 

But a remarkable change of level was effected in the region of the 
Uinta and Wahsatch. Along both of these ranges the edges of the rocks, 
viz., the shore regions, were upturned; in other words, the basin portions 
in the angles between these ranges became relatively depressed. But the 
most singular act of this epoch took place within the land region imme- 
diately west of the lake. Here, the lofty country west of the Wahsatch, 
which had formed the main source of supply for the Vermilion series, sud- 
denly sank and permitted the waters of the lake to extend themselves over 
200 miles westward into Nevada. This was another instance of that re- 
markable law of paroxysmal subsidence taking place in the highest lands 
immediately after they have suffered extraordinarily rapid erosion. 

Between those disturbed Vermilion Creek rocks and the next ensuing 
Middle Eocene sediments, viz., those of the Green River age, there is a 
nonconformity in the basin of Green River, where the Vermilion Creek 
rocks were thrown into folds amounting sometimes to 20° and even 40°, 
and an overlap of 200 miles to the west. 

The deposits, as already described, were comparatively uniform over 
the whole lake. Events at the close of the Green River period embraced 
the relative uplift of all the western half of the Gosiute Lake—that very 
region which had been added by subsidence to the area of the Vermilion 
Creek lake; the plication of rocks of the Green River series at various 
points over the area of the lake resulting in folds of 40° and 50° in 
western Nevada, and the folding of Cherokee Ridge with a dip of 25°. 

The Bridger period north of the Uinta is represented by a lake wholly 
within the limits of Vermilion Creek lake. To the series of orographical 
events which closed the Bridger period, drained the area of its lake, and 
established a small, local, fourth Eocene (Uinta) lake south of Uinta Range, 
we have little clew. 

During the Eocene the whole Great Plains was a land area, and at 
the close of that interval of time a general subsidence of the region took 
place, deepest along the Rocky Mountain foot-hills. The result of this 
was to define the great Miocene basin of the Sioux lake. Probably at 


756 SYSTEMATIC GEOLOGY. 


the same time occurred the subsidence and outlining of the Miocene Pah- 
Ute Lake, which, as before described, stretched from Washington Ter- 
ritory east of the Cascades and Sierra Nevada southward through Oregon 
into California. It is probable that the great eastern fault of the Sierra 
Nevada took place at the moment of subsidence of the basin of the Pah- - 
Ute lake. It is impossible to decide how far the rocks covered by the 
area of the Pah-Ute Miocene lake were folded during this subsidence, 
since even at the close of the Jurassic we know of their being thrown into 
enormous waves. The Miocene lake occupied all the hollows end valleys 
of this post-Jnrassic upheaval, the tops of the high Jurassic folds forming 
islands in the lake. 

In the case of the Great Plains, we are warranted in assuming that the 
subsidence which formed the Sioux Miocene lake was not accompanied 
by any considerable disturbance, since, wherever the deposits of that lake 
are cut through by modern erosion, and the underlying formations displayed, 
they are found to be nearly in horizontal positions. 

This method of general subsidence without fault or fold is further illus- 
trated by the events which took place in the region of the Great Plains at 
the close of the Miocene period and before the Pliocene. At this date the 
whole area of the Great Plains—not only that embraced within the Sioux 
Miocene lake, but a vast amount of its surrounding lands to the north and 
south—suffered so gentle and gradual a depression that, although the sub- 
sequent deposits of the Pliocene Cheyenne Lake enormously overlapped the 
sediments of the Miocene lake in every direction, yet wherever they are 
observed in contact, their angular conformity shows that the Miocene was 
not locally disturbed by the general subsidence. Contemporaneously with 
this gentle wide-spread subsidence of the area of the Plains, that of the 
Pah-Ute Miocene lake was thrown into folds, the Miocene rocks reaching 
in many instances a dip of 25°. At the same time, however, the entire 
Great Basin area sank and became the receiver of the waters of an enor- 
mous lake, covering much of Nevada, Idaho, eastern Oregon, and a part 
of California. The feature of general, gentle subsidence and enlargement 
of lake area is common to the eastern and western post-Miocene disturbance. 


Folding and compression are confined to the Pah-Ute Lake area. 


OROGRAPHY. T57 


At the close of the Pliocene the last prominent dynamic events occurred. 
Both in the region of the eastern and western Pliocene lakes, wide areas were 
thrown into the attitude of inclined planes without either fault or fold. 
This important fact, as I have before mentioned, was first described by 
General G. K. Warren, in his “Preliminary Report of Explorations in 
Nebraska and Dakota in the years 1855, 1856, and 1857.” On page 24 
General Warren says: 

“The question of the slope of the plains is a subject to which I have 
given much attention, from its scientific as well as practical interest. Our 
barometric observations have enabled us, in some measure, to fill up the 
gap between those of Governor Stevens on the north and Captain Fré- 
mont on the south, and thus give us the connected levels over a very large 
area. ‘The observations upon the great Tertiary formation have developed 
the fact that since the close of the Pliocene period the eastern base of the 
mountains, which is the western limit of this formation, has been elevated 
from 2,000 to 3,000 feet above the eastern, and this without there being 
anywhere visible signs of upheaval, such as inclination of the strata. The 
only direct evidence is in the immense denudation which the Tertiary has 
undergone, probably while this elevation was in progress, and which causes 
of denudation must have been gradually extinguished, as there is, at the 
present time, no force at work sufficient to have affected them. 'The evi- 
dence goes to show that the elevation which has taken place since the close 
of the Pliocene period has been in Nebraska remarkably uniform, and along 
a line in a general direction northwest-and-southeast, and nearly coincident 
with the ranges of mountains previously upheaved.” 

This Exploration has shown that the highest point to which the Plio- 
cene strata of the Great Plains rise is in the region of the head of Horse 
Creek, where they attain fully 7,000 feet. From this culmination they 
slope to the north, south, and east, passing under the Gulf waters in Texas, 
and declining to the level of Missouri River to the northeast. By this 
movement the horizontal bed of the great Pliocene lake was tilted from 
3,000 to 7,000 feet, forming the great inclined system of the Plains. Un- 
dulations and faults have not yet been detected. 

Contemporaneously with this, the Pliocene deposits which covered 


¢ 


758 SYSTEMATIC GEOLOGY. 


Utah and Nevada suffered a similar disturbance. From the highest Plio- 
cene level in the region of Thousand-Spring Valley, at an elevation of 
about 6,000 feet, the sheets of Pliocene strata descend in a gentle inclined 
plane east and west—east to the foot of Wahsatch Range, where, upon.a 
north-and-south fault, the edge of the Pliocene sheet was depressed 1,000 
feet ; and west to the eastern base of the Sierra Nevada, where by a similar 
fault the western edge of the sheet was depressed 2,000 feet below its natural 
level. In both the Plains and the Great Basin regions this wide inclined 
tilting of sheets was executed without a fault or a rupture, save at the 
two edges of the western lake, against the Wahsatch and the Sierra Nevada, 
where the old lines of weakness again became the loci of fault, in one case 
of 1,000 feet and in the other of 2,000 feet. 
Regarded chronologically, the periods of orographical activity occurred 

as follows: 

1. Post-Laurentian. 

2. Post-Archeean. 

3. Post-Paleeozoic. 

4. Post-Jurassic. 

5. Post-Cretaceous. 

6. Post-Vermilion Creek Eocene. 
7. Post-Green River Eocene. 

8. Post-Bridger Eocene. 
9. Post-Eocene. 

10. Post-Miocene. 
11. Inter-Pliocene. 
12. Post-Pliocene. 
13. Faults of the historic period. 


The work of the post-Laurentian period was to throw the horizontal 
beds of crystalline sediments into waves wholly within the present province 
of the Colorado River, viz., from the Rocky Mountains to the Wahsatch, 
inclusive of that range. The general post-Archeean orographical period 
covered not only that which was folded at the close of the Laurentian, but 
extended itself westward over the whole breadth of the Cordilleras. This 
enormous crumpling was accompanied by the great faults at Red Creek 


OROGRAPHY. 759 


(Uinta) and at Cottonwood (Wahsatch). Elsewhere faults and dislocations 
were accompanied by enormous and repeated intrusions of plastic granite. 
In general, it was the west half of the post-Archan uplift which resulted in 
the grandest mountain forms. 

The post-Carboniferous movement defined a continental body from 
the Wahsatch to the longitude of 117° 30’, its greatest elevation being upon 
the west, as is shown by the enormous amount of sediments delivered 
directly under those western heights and by the excessive dislocations of 
the crust at that longitude. 

The post-Jurassic period had its action altogether confined to the post- 
Carboniferous continent, and a till then submerged region extending 200 
miles west of the continent, which at this period became crumpled and 
upheaved above the level of the sea. It is also noticeable that the western- 
most limit of the post-Jurassic upheaval was that of the most powerful 
compression. 

The post-Cretaceous period covered the present province of the Colo- 
rado and that of the Great Plains. Its result was the obliteration of the 
mediterranean ocean, and the development of powerful folds and of great 
elevated plateaus whose surface was comparatively undisturbed. The 
most intense crumpling and local disturbance was at the extreme western 
edge of the area acted upon, viz., in the region of the Wahsatch and Uinta. 

These three periods—post-Carboniferous, post-Jurassic, and post- 
Cretaceous—taken together, were the main building-times of the modern 
American continent, and each of these orographical disturbances was most 
violent at the western edge of the region involved. All of the three dis- 
turbances have been confined to regions of marine sedimentation, and in 
each case the age of the upheaval came immediately at the close of a long 
interval of conformable sedimentation. 

The continent having been completed with the exception of the Pacific 
Coast Ranges at the close of the Cretaceous, subsequent disturbances of 
whatever character are not to be measured by their relations to the sea- 
level, but are simply the foldings, upheavals, and subsidences within a con- 
tinental area, and may only be measured by their relations to contiguous 
land or lakes. 


760 SYSTEMATIC GEOLOGY. 


Each of the great groups of conformable sediments during the process 
of their formation covered regions of successive gradual subsidence, and in 
the nature of this sitbsidence it is evident from the relations of the lower 
and upper members of the same series, first, that the beds are thickest 
next the source of supply, according to the ordinary rule, so that the forma- 
tion as a whole has the section of a wedge, the greatest subsidence always 
taking place at the thickest end of the wedge, and the descent being 
directly proportioned to the amount of material. This is clearly shown in 
the conformable body of Paleozoic rocks, and in the Mesozoic series east 
of the Wahsatch. A subsidence of at least 10,000 feet evidently took 
place during the deposition of the Mesozoic east of the Wahsatch. Now, 
this local sinking represents one of two processes: either the bending down 
of a thin crust underlaid by yielding material, or else the actual displace- 
ment of solid subjacent material, which, under the loaded spot, acted as a 
comparatively plastic body. . 

There are, therefore, two entirely different types of subsidence, one 
the gradual sinking of a region by loading, due to sedimentation, in which 
the most heavily loaded locality goes down deepest. This subsidence, from 
the nature of the sedimentary sections, is seen to be of the slowest and 
most gradual type. The other is a sudden paroxysmal subsidence on a 
plane of fault, in which the region lightened by erosion and removal is the 
one that goes down. 

In the upheaval of wide areas there are two main noticeable types of 
operation—one the lifting relative to the sea-level of broad regions which, 
after upheaval, may be left horizontal or in gently inclined planes, their 
surface showing neither fault nor fold; the other, the well known operation 
of plication, by which actual deformation of the crust takes place, resulting 
in folds and faults and the tangential crushing of rocks. 

In the case of such an action as that which tilted the whole province 
of the Great Plains into its present inclined position, it is evident that there 
was both upheaval and subsidence relative to the sea. The sheets of strata 
which formed the surface of the plain are of lacustrine Pliocene. Their 
highest point, of 7,000 feet, is higher than all but the highest summit of the 
Appalachian system There was no mountain barrier along the eastern 


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OROGRAPHY. 761 


margin of the great Pliocene lake. Had that lake been at 7,000 feet, its 
fresh waters must have extended over the whole of eastern America and 
over the top of the Appalachians, which is impossible. On the other hand, 
when we approach the Gulf shore of Texas, in the region of Galveston, 
these fresh-water Pliocenes are seen to pass under the salt water of the 
Gulf. There has been, therefore, between the two sides of the lake, actual 
depression below the sea-level and actual lifting far above the former 
altitude of the lake. 

In the case of the post-Cretaceous upheaval a very wide part of the 
area involved, including the province of the Plains, although lifted above 
sea-level, was not locally plicated or faulted, but the extreme western limit 
of the same area of dynamic action suffered the enormous folding of the 
Wahsatch and the Uinta. It is, therefore, possible to have contempora- 
neous general uplift without any local disturbance, passing and merging 
into a region of great horizontal contraction. 

In this complicated history, therefore, have occurred both upheaval 
and subsidence as related to the sea-level; plication, always greatest at the 
western edge of the area disturbed; the formation of folds 40,000 feet from 
summit to base; the development of faults with at least 40,000 feet of dislo- 
cation; the tilting of horizontal regions into broad inclined planes without 
a disturbance; and the division by complicated fault-systems of wide 
areas into numerous separate blocks, of which some are depressed below 
the level of their adjacent companion blocks. 

It is also a general law that those regions which experience elevation 
without local disturbance are the regions of relatively thin sediment super- 
posed on a comparatively unaccidented Archzean foundation, whereas those 
which suffer the extremest plication are covered by the thickest deposits 
overlying and adjacent to the greatest Archzean mountain ranges. 


APPENDIX: 


GEODETICAL AND TOPOGRAPHICAL METHODS USED ON THE GEO. 
LOGICAL EXPLORATION OF THE FORTIETH PARALLEL. 


By JAMES T. GARDNER, 


Assistant in charge of Surveying. 


The territory surveyed is a belt about 107 miles broad and 800 miles 
long, extending from the eastern foot of the Rocky Mountains to the Sierra 
Nevada of California, or almost across the Cordilleras of North America, 
where they are broadest. It is included between the meridians of 104° 30’ 
and 120°, and the parallels of 39° 30/ and 42°. The western half of this 
region is an arid mountainous desert. The eastern half, having a much 
ereater elevation, is not so dry, although in large part desert. The Union 
and Central Pacific railroads, which now traverse this section, were not built 
when the Fortieth Parallel Exploration was begun, and no maps of the 
mountain ranges existed upon which even the roughest geological work 
could be based. 

For the purpose of studying and drawing the geology of this area, it 
was therefore necessary to make maps on a scale sufficiently large to show in 
their true relations the principal topographical features and their characteristic 
differences of form. This duty was assigned to the surveying department, 
with instructions to produce a map of the territory examined, on a scale of 
an inch to four miles, on which should be laid down the general con- 
tours and elevations of the mountains and plateaus, the drainage-systems, 
roads, towns, &e., with such accuracy that errors in relative positions 
and distances between points should not be apparent on the given scale. 
It was evidently impossible to accomplish the result by ordinary modes of 


764 SYSTEMATIC GEOLOGY. 


recomnoissance; and with the time and means at command it was equally 
impossible to carry over this great area of 87,000 square miles a topo- 
graphical survey like those of Europe. Maps for the geological purposes 
in view, however, must be similar to European ones in character, only 
much less accurate in detail. It was, therefore, considered best to use in 
the Fortieth Parallel Exploration the general plan of a regular trigonomet- 
rical survey, modifying methods to obtain the desired grade of precision 
and detail. The work is consequently based on a connected system of 
primary, secondary, and tertiary triangles, by means of which all topo- 
graphical features were determined. 


PRINCIPAL TRIANGULATION. 


The peculiar form and climate of the region greatly facilitate triangu- 
lation, abounding as it does in sharp rocky peaks bare of vegetation, 
enough of which rise to altitudes of 10,000 to 13,000 feet to furnish inter- 
visible points 60 to 80 miles apart, so situated as to form well conditioned 
triangles, while the purity of the atmosphere renders distinct seeing possible 
at long distances. 

Stone cairns were placed on the peaks selected for stations, and were 
the only signals used; but these being invisible, except on shorter lines, 
exactly the highest points of the mountains were usually observed. These 
culminating points of Cordilleran summits can generally, by a practised eye, 
be determined within a very few feet. Along three quarters of the belt 
triangle-sides have an average length of about 70 miles. In the remain- 
ing portion the average length is about 54 miles. The longest line is 115 
miles. 

From Peavine Mountain (long. 120°) to Medicine Butte (long. 111°) 
the average error of closure, after reduction for spherical excess, is 13”; 
from Medicine Butte to Separation Peak (long. 107° 80’) the average 
error of closure is 80”; from Separation Peak to Sherman the average error 
of closure is 15”. 

The errors of closure in triangles were distributed among the angles 
according to judgment of the weight of observations from the number 
of pointings, special characters of the objects sighted, and agreement 


GEODETIC APPENDIX. 765 


between independent values. The whole figure of the scheme was thus 
adjusted and fixed in the relations of all its parts, without reference to any 
bases of verification or resulting geographical position of stations. 

Most of the angles were observed with an eight-inch Wurdemann the- 
odolite reading to 10”. Some were measured with a six-inch Wurdemann 
circle reading to 10”. 

From Peavine Mountain to Medicine Butte the observations were made 
by myself in the years 1867, 1868, and 1869. Between Medicine and Sepa- 
ration peaks theyawere made by Mr. A. D, Wilson in 1872. From Separa- 
tion to Sherman the observations were made by myself in 1872. 

At twenty-one of the principal stations azimuths of Polaris were 
observed, the time being determined with a sextant. The latitudes of five 
stations were determined with a zenith telescope by myself. The latitudes 
and longitudes of three others, Verdi, Salt Lake, and Sherman, were deter- 
mined by the United States Coast Survey with the utmost precision. Two 
of these stations, Verdi and Sherman, are at the extreme ends of the chain 
of triangles, and Salt Lake is in the middle. 

The triangulation was developed from an astronomical base just west 
of the 118th meridian. 

This base is a line about 64 miles long between the summits of 
Tarogqua and Star peaks, which lie very nearly north and south of one 
another. The latitudes of these two stations were carefully determined 
with the zenith telescope, and the azimuth of the line joining them observed 
at each end. These azimuths, corrected for difference of longitude, agreed 
within 14”. 

The length of this base, as computed from the observed latitudes of 
its extremities and its azimuth, is 3369’’.7 or 64.6613 miles at sea level, to 
which all results are reduced. 

When the attractions of surrounding mountain masses on the plumb- 
line at the ends of the base were calculated by formule used on the British 
Ordnance Survey, it was found that the base required a plus correction 
of .004 of itself, the computed attraction amounting to about 4” to the 
north at Star Peak, and 9.5” to the south at Tarogqua. On account of the 


well known uncertainty of these formule, it was decided not to make the 


766 SYSTEMATIC GEOLOGY. 


full correction obtained by them, but to multiply the astronomically meas- 
ured distance by 1.00263, because this corrected base would give a 
geodetic difference of longitude between Verdi and Sherman exactly 
equal to the astronomical difference of longitude as determined by the 
United States Coast Survey. 

The adopted length of the base from Star Peak to Tarogqua Peak is 
therefore 64.8313 statute miles, and the geographical positions on Maps IIL, 
IV, and V. were calculated from it, as it was necessary to proceed with 
their engraving before the eastern end of the belt was surveyed. 

Checks indicating the probable uncertainty of results were obtained 
by comparison of observed azimuths with the geodetic, and by comparison 
of geodetic and astronomical latitudes. 

The Salt Lake azimuth being carried through to the most western sta- 
tions, the azimuth there observed differed from it +18”. The differences 
between observed and geodetic azimuths at intermediate points, going from 
east to west, were — 4”, 0”, + 10”, +7”, — 3”, +15”. 

The following table shows the agreement of observed and geodetic 


latitudes: 
COMPARISON OF OBSERVED AND GEODETIC LATITUDES. 
Ze ga [ge [sz 
rt (sl os 3 os os 
=o oe < 
2:5 uo 2 .|e- 
Stes 5 Oo ise] ao8 
Fel ecs sy a ae Sqr|/ 22a 
g | 88 sq [Saucleas 
co 2 so ®eyo.(|oo0y 
3 mS 3 Zooujarceds 
Name of Station. 3 Ze L His Astle) aa fees 
= 236 6 |ae ld¢slisas 
= ood | § | SEa loseul eos 
2 eg g 235 |S°Siisus 
e Seg : PHE@Igestfadg 
3] 364 & |eudiu6e wo 9 
3B Sua B | SSB ssa | 28 oo 
° o a ° io) =} 
: = —,, ;,  — ee 
° ’ a” / , a” au 4 “ur Mu 
Salt)Lake; Tabernacle Staff'cs.sscscccccedscs sseecissssiaseueceecces | 40 46 06.0 | 46 06.0 0.0 | 46 10.5 | 46 08.50| —2.00 
Pilot} Peak. .:.c<cjossicscicteeeic sale vsls dee cis vewaes Cossnicenaseeeuiactees | 41 OF 12.2 | Or 09.70-+ 42.5 OI 12.2 | or 12.20 0.00 
Ruby Valley: astronomical/Station .-....cs<ccceciesssivecvsiscscsve ssc | 40 02 47.4 | 02 41.36 | +6.04 | 02 43.4 | 02 43.86 | +0.46 
Star! Beale: sos cioecs cceamseeecec cee ee ceneeese ese ceeeeaeereenee | 40 3x 13.5 | 3x 14.10 | —0.60 | 31 16.7 | 31 16.60| —o0.10 
Tarogqua Peas . 5.2.02. cccccccsccosescsecccecsriccesissctiasecese sss] 39/35 03-8) |13455:00/|.--6.201)|1 44053285 |qaucSex0]| Et 4ego 
Wadsworth astronomical station ...........00.2-:ceeeeeeeeeceeees 39 37 30-0 | 37 24-59 | +5-41 | 37 28.0] 37 27.10] —0.90 
Peavine Mountain (Verdi) </ cc rans seek cnee sia eeneriee eee 139935) 28>7,\|(95) 28>471\| | --0-23) reese rece eee eiece|cmeceeels 


From the final column of this table it appears that the difference in 
latitude between results by triangulation and zenith telescope observations, 
corrected for attraction of mountains on the plumb-line, is much too small 


to be seen on the maps. 


GEODETIC APPENDIX. 767 


In 1872 a base of verification was measured with a steel tape near Fort 
Steele, in longitude 107°. When reduced to sea-level it is 4.7900 statute 
miles long. 

The length of this base, as computed by triangulation from the Star 
Peak base, is .0004 greater than by measurement. 

When the geodetic difference of longitude between Salt Lake and Sher- 
man was calculated by the Star Peak base, it proved to be .00256 smaller 
than the astronomically measured difference. Owing to the positions of the 
mountain masses in relation to the United States Coast Survey astronomical 
stations at Verdi, Salt Lake, and Sherman, it is probable that the astronom- 
ical difference of longitude between Verdi and Salt Lake is too small, and 
that between Salt Lake and Sherman too large. It therefore seemed prob- 
able that the discrepancy between the astronomical and geodetical differ- 
ence of longitude from Salt Lake to Sherman was partly due to the Star 
Peak base being too small, and partly to the astronomically measured dis- 
tance being too long. 

For this reason the triangulation for Maps I. and II. was calculated 
with the Star Peak base, multiplied by 1.0013. There remains a disagree- 
ment of 30’ between the two methods of measurement of the distance 
from Salt Lake to Sherman. The agreement between observed and com- 
puted azimuths showed that no large errors existed in the adjustment of the 
triangles. 

Geographical positions on Map I. are computed by triangulation from 
the United States Coast Survey astronomical station, Sherman, while those 
on Map IL. are reduced from Salt Lake as the initial longitude. Between 
these two maps there must therefore be a disagreement in geographical 
positions. The error in either will be equal to the true station-error at the 
initial astronomical station, combined with the error of the triangulation. 

I am inclined to believe that the probable uncertainty in distances 
measured by the principal triangulation does not exceed 0.001. 


SECONDARY AND TERTIARY TRIANGULATION. 


Secondary points were located by cuts from the principal stations, and 
from these a smaller system of triangles was carried over the country by 


768 SYSTEMATIC GEOLOGY. 


the topographers. The angles were measured with the gradienter, a light 
instrument having a very effective telescope and a four-inch circle reading 
to minutes. Rocky peaks, five to ten miles apart, commanding the best 
views of surrounding country, were chosen as stations. Signals were seldom 
used, the summits being generally sharp enough to be observed with suffi- 
cient precision Elevations of stations were determined with the mercurial 
barometer of James Green. 

Base stations, where the barometer was continually observed while the 
survey progressed in the neighborhood, were established at intervals of 100 
or 150 miles along the line of work. Field observations were all referred 
to one or more of these bases, and the bases afterward connected by syn- 
chronous barometric observations with the levels of the Pacific railroads. 


TOPOGRAPHICAL METHODS. 


Regarding its trigonometrical foundation, the Fortieth Parallel work is 
allied to regular surveys; but the topographical methods employed were 
more like those of the best reconnoissances. 

From each occupied station the adjacent territory was carefully sketched, 
in plan of drainage, in leading horizontal contours, and in profiles. As 
many points on these sketches were located as could be cut by intersecting 
lines from the occupied stations, and their altitudes determined by angles 
of elevation and depression; these points fixed by measurement are con- 
fluences of streams, lakes, buildings, and conspicuous rocks, knolls, and 
peaks on mountain spurs and crests. 

In a dry region of sparse vegetation, where the ridges are serrated and 
water-courses and ravines deeply marked and clearly visible in the distance, 
where every mile of territory is overlooked from bare commanding summits, 
and where the atmosphere is remarkably clear, this method of taking topog- 
raphy gives a far closer approximation to the truth than would be possible 
in a country where drainage-lines and details of form are masked by foliage 
or dimly seen through moist hazes. The sharply cut features of the Cor- 
dilleras stand out so boldly that the topographer has only to locate enough 
points and make careful contour, profile, and drainage sketches, in order to 


produce a very fair representation of the country. 


GEODETIC APPENDIX. 769 


The maps were made by laying down on polyconic projections the 
geographical positions of principal and secondary points, then plotting by 
intersections the tertiary stations and located points. Between such of 
these as are on streams the water-courses were filled in from drainage 
sketches, and from profile sketches the slope angles were estimated and the 
contours spaced in between points whose altitudes were determined instru- 
mentally. 

The contours, therefore, are located by barometrical and trigonomet- 
rical measurements at certain points and sketched between these with the eye. 


49 K 


GENERAL INDEX. 


OBSERVE SPECIAL LISTS OF AUTHORS, CANONS, FOSSILS, LAKES, MOUNTAINS, PASSES, PEAKS, AND 


RANGES. 
Page. Page. 
Actinolite in Archean quartzite ..-..-..------+----- 69 | Andesite (augitic), River Rango .----..--.--------- 572 
Adara, Donegal, Ireland, granite......-------------- 60 Steamboat Valley .--..--.----- 576, 577 
Ada Springs, basalt of .-.....--..------+----+--++++-- 653, 654 Susan Creek, Seetoya Rango -- 573 
trachytoof....-....---------2. + +--+ 581 Truckee Caiion..- 576 
Agassiz, Louis .......----------------2e-ee22 eeeeeee 4717 Tuscarora.-.-.---- . 572 
Agate Pass, basalt of......--------------++--++---+++ 661 W achoe Mountains....-...----- 571, 572 
Weber quartzite of - --- 219 Wadsworth .....-.-...-------- 576 
Age of dryness in interglacial period. 524 (hornblendic) .-..............-------.--=-- 562 
Vermilion Creek group .----- --------+------- 377 Berkshire Cafion, Virginia 
Albion Peak, Coal Measures (Upper) of. ------------ 224 (Rane Oeceaeera atm cincisies sala 566, 567 
Albite in granite of Humboldt Range ..-..---------+ 64 Carlin Peak.........-:-.s---- 563 
Alkali Flat, Diamond Valley 503 Cortez Range)....0---=s<- sos 563 
Smoky Valley ...-..---.--------++---+-- 503 Crescent Peak .-....-...----- 504 
Alkaline carbonates of Lake Lahontan 513 Gosiute Valley ....-..-.------ 562 
deposit, North Fork, Humboldt.-..-------- 502 Palisade Cafion -....-.------- 563 
incrustations of middle Nevada ....-...--. 502 Truckee Cafion, Virginia 
Allen, O. D., analyses by 496, 511 Lit saceoussopaye sosecese 505, 566 
Aloha Peak, basalt of ..-..-----------------++- 669 volcano of Lassen's Peak....-------------- 566 
rhyolite of ...---------------- +++ C 645 | Andesites, succession of...----.--.-------------+---- 684 
Alpine Trias fossils, Desatoya Mountains...--..---- 283, 284 hornblendic, Kamma Mountains. -... - 564, 565 
SOChloN-ceshecesacseseserisawcesesenc w= 269 SNCIGACILCS ea = asin a-ew el ew eenmee nc censsee 562 
Star Caiion 276, 277 distribution of. 
work of glaciers 483 | Andrews, Dr., experiments of.....---.-------------- 
Alps, arrétes of .---------.- 472 | Anita Peak, basalt of ..-...---..----+-+22+eeeeeeee es 
Altitude of Lake Lahontan - 505 | Antelope Creek section, Trias.. 
Ammonite Cafion, Trias of ....--.------- 283 | Antelope Hills, rhyolite of ..--- 
Amphibolite, Grand Encampment Peak...---.------ 40 | Antelope Island........---- 
Amphibole rock, Garnet Cation, Uinta Range. --.... 43 | Antelope Peak, basalt of......-.--------------+++-+-+ 
Anabé Island, thinolite of......-.-.----------- 515 | Antelope Spring, Wahsatch limestone of ..---------- 196 
trachyte of.....-.---------- 601 | Anteros Cafion Trias....--.------------- pease stO50 263 
Andesite of Cedar Mountains 562 | Antimony Cafion, Augusta Mountains, andesite (au- 
Clan Alpine Caiion, Augusta Range. .----- 564 gitic) of 57. 
(Gita iG) eeoteaneaacoossneeoenec esse ceeceonc 571 rhyolite of.....--------+--------+- 632 
palagonite referred to..-..--..---- 419 | Antler Peak 219 
(augitic), Antimony Cafion, Augusta Upper Coal-Measures of .-.. : 225 
Mountains 2o2ccacccecececens 575 | Apatite in hornblendic plagioclase schist. . 33 
Cedar Mountains 571 | Aplitic granites of Colorado Range. ..--.---- A 22 
Cortez Range.scccs seen oo --= 574 | Appalachian series compared with Cordilleran ...-.- 536 
Crescent Peak, Augusta Moun- Appendix, geodetical and topographical. .-...------- 763 
TAINS eeercs = eeeresesseac esa 575,576 | Aqui Range, Cambrian quartzite Ofeecececssemieceees 185, 186 
Egyptian Canon. . 572,573 | Archwan and Palmozoic, relations of .----..--------- 122, 123 
Jacob’s Promontory ..--------- 574, 575 anticlinal of Colorado Range ---- 21, 22 
Last Chance Spring ..- ------- 572 beds, absence of chemical action between 
Melrose Mountain...-...-.----- 572 contiguous strata ..-..-.---------- 112 
Palisade Cafion.......--..----- 574 chemical persistence of....-.-.------ 104 


BR 
Bue 


Heme ewe 


vi 
Se) a hi 


uf 


ee ee Ee a 


ae 
Bann B 


Snetesschiger. Wet Hambold: a 


& 


# 
ry 


Posqeep Ses 
pewolorical smplictty of Candilleras...... 
primitive swmamiis of _..........-..---..-- 
qmerurite, actinolite im -.--_---.-.--..---.. 


Baw ie 


B 


B 


| 
H 
1 
2 
HB4OHR BoNBes 


Humbeld: Range, accessary min- 


Rewinss 

Sel: Lake and the Promontary-.. 
Seciegs Gees 
Shoshone Bange ..-............-- 
ee 


jenessenwane Me pe 


Gstribution of ...................... 32538 


‘Wahssitch, relation to liter rocks..-..-- 
Area and aspect of Lake Lehonten --.........---.... 06, Wi 
and Exploration of the Forticth Parallel -..... 


INDEX. 


Page. 

Ashley Park, Paleozoic....- -- 148,149 
Aspen, Fox Hill Cretaceous 326 
Aspen Plateau, Vermilion Creek group of -..-.....-- 370 
PASLODP Res eLrachy too fieeaeeseeeacsies saan menieee moe 602 
Atlantosaurus beds....- 
fossils ... 

Atlas accompanying Fortieth Parallel Report. 


J Nae eG Sen Seeeee seeesaces: Seaneercecccecas 71 
Augusta Mountains, Antimony Caiion, andesite (au- 

Pati) Oo os co-coaneSeeead 575 

Archean rocks ... 79, 80 

basal eee ene mae ee aoe 663 


Clan Alpine Caiion, andesite. -- 564 
Crescent Peak, andesite (au- 


PUT) Sacco SHER OSoSSSQURCEE 575, 576 

PTAnILO seeaee eee ena=aeien sea awe 80 

Jura.... 294 

rhyolite. 631 

Trias .. 281 

Austrian Alps, Trias of....-.....- BOSS CD RE SSR SE OSEO 74 
Authors, Agassiz, L ............- See eeeas es seca ae 477 
Allen, 0. D..-. ---- 496, 511 
Andrews.......- 78 
Babbave\-n.~<2--a<i<> 727 
Bonneviile, Captain ------- - <5. <2 55. 2-28. 1 

Bradipyy rank? Hieseesceanaioasaen=eenaaa 38, 178 

Dye Gue, \Wi’od lace ac aacdcassacsneseccecase 450 
IBrewstersbolieee sencene ses eens eee ance 131 

Bunsen, R ------ -417, 678, 691 


Clayton, J. E...-. -197, 198, 213 


Cope, E. D ...- 353, 354, 376, 391 
(O5faLA SYNOTh sonmossonceosenonessoceaosesta 417 
Mana Steen ecss see se sana 408, 410, 455, 517 
Danae) pera 117, 191, 459, 465, 517 
Darwine Gharlegmencesseesessaseesn ancl nee 715, 716 
Dawson, G. M... 101, 103, 459, 463, 464 


‘Delabeche cecesaeesetaae- sana caaseeccnces 117 
Delesse tern saeeeerneee eens an aneanencincas 706 
Duong tienen aaaasecenanans cs ceccas = 698 
ihren bere Oakes esses sae erase eens ee 420 
MMOUS | Sah ee sesan aan cesnceecice=sce 4, 303, 324, 

433, 449, 551, 572, 613, 629,743 
Hnvelmann Or acaae eee seeeaeacaiesace=coe= 211 
Rrémonicd ODN) Ges enaseceaen ese =asnee a= 1 
ishereneve Cin eameeateee cance s se ceecaes 698 
TENG) Sas sonosbaossads <= Sil 


GatboWa Mier aceeenenemcoe ~- 275, 279, 450 
Gale, L.D'----..-- cess ata 497 
Garduer, James T . saccceecrsegaso+cs 20, 763 


Gilbert, GK... .. 445, 466, 490, 491, 492, 493, 523, 525, 
548, 5£0, 581, 633, 725, 746, 749 


Grinnell "GeBlee ee cceeenee eee 132, 408, 410, 455 
(Gnmmisone-===--—--=s- eee eane seers 1 
Hague, Arnold ....-..--..--- . 4, 551, 602, 629 
BEGAN) --oscedesnas peeps ceboseeEeoosee 79, 110 
“Hall, Prof. James.-......- 187, 206, 207, 210, 20, 294 
Haydons ieiViecs<=sieeeeer= vee. 2, 3, 127, 298, 347, 348, 
354, 391, 445, 451 

Herschel..-..-..-- co -- 703, 727 
Hochstetter, F. von BASU EEE ORCS 649, 687 


Hopkins, William .....-...--.- 696, 697, 701, 702, 718 
Humphreys, General A. A 427 
Hunt, T. Sterry 
TANG Or seen eee eee sees == 


Marsh, O. C-. ..285, 423, 439, 443, 445, 449, 450, 454, 591 


Marvine, Archibald R ....-........-...... 23, 649 
Meeioih cece steeeae 211, 328, 423 
Meek and Hayden ............. cot eeacnscs 331 
Muir, Jobn 417 
Newberry, J.S 331, 353 
Pfafiiceas-esacnianaeeean 693 
Powell, Maj. J. W..--. 148, 290, 331, 385, 328, 445, 448, 

450, 478, 633, 735, 748 
Pratt, Archdeacon: sessse.----eeacesmee === 705 
Unit) Eo bemanee mae sco cece mac OmOnCae SEC CUISSES 477 
Pumpelly, Raphael ..............---...--- 51, 105 


Richthofen, F. yon... .549, 550, 554, 649, 681, 682, 687, 
689, 707, 710, 711, 716, 721, 722, 724 


Scrope, Poulett Soresosee sass VERT 
DleOLen sees ae eee eon een ane =e eeeee 114 
SUM PSN see eeleecaa eee enceseaenee one 1,211 
Smith, J. Lawrence - 499 
Stansbary, H .-...-- 1, 497 
Stevenson, J. J.- 331, 332 
SUOKES eos sncee = on omn ee eena sear =n cece n = 705 
Rip EN esecoseesecccncs sano san oer e Sse 706 
Thomson; AMES == 2o— 2 saneaw aa cone aaenee 704, 728 
Thomson, Sir William 696, 697, 701 
Waltershausen, Sartorius von --417, 707, 718 
WE ibd BG Ta 7 eS eee cee sacesasoae 79 
Warren, Genenal G. K..--..---...-.-- 2, 427, 483, 757 
RWiheelet Gee io ean enone eee eee 490 
Whitfield, R. P -..-. -187, 191, 206, 207, 210, 280, 294 
Whitney, J. D...... --. 2,3, 266, 295, 450, 460, 689 
WWalliamson, Major <oo a. cacaacnccoaeueecs 1 
Woodward Ro OWirere----n-canmemacee sans 52, 53, 499 
Wari oh Cmee eno ace epee eccee eee 420 
Zirkel, Ferdinand...-...... 547, 550, 551, 564, 569, 572, 


580, 591, 599, 601, 604, 605, 613, 639, 647, 
650, 656, 657, 666, 669, 675, 682, 719, 722 


Author's share in this volume .-........-.---------- 4 
Avalanches, modern increase of .........----------- 526 


Babbage - -- 


Babylon Hill limestone, of Wahsatch .--...-.-.-..-- 206 
Bad Gans @aan a aan seceee eee manometer 9 

Bridger group of.....-... poe socd 397, 398, 399, 401 
Barrel Springs, Vermilion Creek group -.-.-.------- 364 
Basalts 


Ada Springs. .-. 


A PALGULSSS paneeeteenec cera aeeaene eames 

ENTE RO aan capone Seconds Aas eaaososcc 

Anita Peak ....... 

Antelope Peak ..--- 

Augusta Mountains. 663 
Baraljpbeakysnasaccsseessoeee=aantensaaves == 669 
Bayless Cafion ...... ..---..--..---e202------ 668 
The Beehive ---..-...c<0on=----~-=~ = 659 
Black Rock Mountains ...-...----- .. 609, 670 
Buffalo Peak..-...-.---- Sos . 654, 665 
Gave GanOn assoc se se cewceneresecsoes=s-ce=- 660 
Chataya Peak ...........-----------sseenees 664 
Clark Station ....-.. 67 
Cortez Range .-.-..-- - 660, 661 
Curlew Valley ---- 658 
Dui Crees scans ceeeescenncceneeseesnse= = 658 
Eaglo Lako .........------------se+- -ooetes 660 


774 


Basalts, Eldorado Cafion .........-.2-sseces-seeeseee 666 
Distlead Mountains -ecssecsseeecesereenaes 654, 657 
Wishi€reek Mountains: 5. .<-222. 022 cecccre os 664 
Fortification Peak 656, 657 
Golconda:Rass \-aeqse-esccceeacniaeeeoceecas 664 
Granite Mountain \.55..<cc-ceecseestecasenas 665 
Granite: Point? s2-5--<ccasce-seccs seeee acess 668 
(Mian tz Ped) ssc seenaseacctees see deenasdaae 654, 657 
Hardin‘ City .--..----. - 670, 671 
Havallah Mountains .. 664 
Humboldt River ....-. 660 
hy ali tA pON ce oeseeeeereede eee cece serene aae 662 
indian? Passs-coas cesses ss esaeacensaaeaee eee 667 
Kamma Mountains...- - 668, 669 
Kawsoh Mountains ..- 674 
Lovelock's Knob: .:-2.-ss6.sccesssscacseseses 668 
Mhovelock’siStation sescassccoacceenecsadecses 666 
IMadelin: Mesa) saes---sasecescusseccccs«scese) OlliOis, 
Matlitiec.ss-cccetesscs, 658 
Mirage Station........ 675 
Montezuma Range. --. 667 
MopungiHills: ck fasccecscatwcetecceusestece 666 
Mount) Weltha, ....-222c.ecetsce-cosescseu 654, 656, 657 
Mud Lake Desert - .-. 669 
Navesink Peak .....--.. 654, 655 
Mephelin@s-ccecesacs 656 
North Park 653 

658, 659 
666 
Pah: UteiRan le ...2--5-<c00cccs ccontseececciss 664, 665 
palagonite, dependence of 419 
palagonite-tuff .......... 671 
Piiion' Pass = --....-. 660 
Pinto Peat. cntceccssccusssitarccesesrencens 660 
Rabbit Ears Peak 653 
Ragan’s Creek ....-.. 664 
Railroad Caiion 660 
The Rampart... ... 654 
Red Dome 658 
relation to rhyolites 687, 688 
ROG syatered ketene sern <iocenicctwecee'saaccsiscesoe 664 
Rocky Monntains..-. 22. c00s.cceccesennss ans 653, 654 
IRUDYZETOU Deeees o<cass caeeen pee sananeeasc ce 659 
Shoshone Lake, relations to..........-...... 457 
Shoshone Mesa............ --. 662, 663 
Shoshone Range............-....--- ere oO 662 
SnakoPlainesrcccssaecisitsscec coossccccesece 593 
Sow/Springsvecce.cics see's 664 
Spruce Mountain 660 
Stony Point........... 663 
Table Mountain 664 
rnc ket! CANON scccaceecceesctencssccursecce 77 
Truckee Range... -2.:, <<. .0csedtieeeeeccecce. Olzy 07d 
Truckee:Station :2.<:..i-ccceseceseeeess acne 676 
Virginia Range 
Wagon Caiion .......... 
Watch: Hill--oetee seas 
Wihirlwind (Walley ceceesnecs.nceauacacecones 662 
Wihite Plains feswacewses dsiccsccwccsececacass 75 

Basalt(Peakjbasaltiotussseccscoccseccs-ccccceciseesce 669 

Basaltic plain, Shoshone Valley ........---...-...--. 679 

Basin ranges .ss.00iscecececntins San-tssussseseeece 736 

Basin of Utah, Humboldt group of .......-.......--- 434 

Battle Mountain, rhyolite of ..:-....-....-:.-cesses- 635, 636 

Upper Coal Measures of .......... 225 


INDEX. 


Page. 

Battle Mountain, Weber quartzite of ...........---- 220, 221 

Bayless Cafion, basalt of .......---....---+---------- 663 

rhyolite Of -esnenteaameeatereeneeene 644 

(Bears Riven -tesecsesee esac ce clean 12 

Bear River City, Fox Hill Cretaceous 325 

Bear River Platean, Vermilion Creek group of .-.-.-. 37L 

Beckwit Dizcc-ccjscocestaccscss sceamnesesn secs e es 1 

Bechives; basalt:0f-m-cocec ooo seaeeclec=sesaeeeeerioaes 659 

rhyolite ofc ssessco-ssessee, 613 

Bellevue Peak, Archean Rocks of.-.-.. 35 

Colorado Cretaceous 310 

Berkshire Cafion, dacite of.--.-.....-. 570, 571 

rhyolite of----.:.<-- 652 

Bifurcation of Truckee River...-....-.......-..---- 405 

Big Horn Ridge, Fox Hill Cretaceous.....-.....----- 326 

Green River group of . - 387 

Big Thompson Creek, Colorado Cretaceous . 308 

Dakota Cretaceous . 9 300 

DOLD eee asec ase ne eae 286, 287 

Pliocene conglomerates of -.. .. 431 

TriassiGhesscsoeeteercnes case 251, 252 

Bingham Cafion, Weber quartzite of ........-...--- > 213, 214 

Biotite-hornblende, granite type IIL . 108, 109 

Bishop Mountain, Green River group of. .......----- 387 

Vermilion Creek group of ..-...--- 368 

Bitter Creek region, Laramie Cretaceous of....-..-. 335, 336 

uplift in Vermilion Creek group.....-- 369 

Black Butte, Laramie Cretaceous ....-.-..---- - 336, 337 

Black Butte Station, Vermilion Creek group -.----- 364, 365 

Black: Cationirhyoliierccnsssesacncmeeaceaas scteaesee 642 

Black Rock desert, efforescence...---. 513 

Black Rock Mountains, basalt ..-..... - 669, 670 

rhyolite - 648, 649 

Black’s Mork, Juranca-caccedesneeaaetecneseeaeeoee 291 

Palie0z0l0ze ec cscesrecence veewan/anianestse 142 

Black shales, Wahsatch limestone. .....-...-.---.--. 199 

Blue Ridge, Wahsatch limestone..........-......--- 207 

Blue Mountain Range ......--- : =a 452 

Boise Basin, Pliocene .... a Eas 440 

volcanic rocks of, reJation to Pliocene in 592 

Bone Valley, Humboldt group of ...--..-...--.------ 439 

Pliocene vertebrates .----..-...-s2-.000 439 

rhyolite 617 

Bonneville, Captain : 1 

Bonneville beach, altitude of Aon 492 

Bonneville beds, Gilbert's deductions from .--..----- 523 

Bonneville Lake, terraces of ...........-.--.----2e0 436, 437 

outlet, Red Rock Pass............. 492 

Bonneville’ Peak -s2ec-s3-.c--cen<-caseeastes ocr eee 185 

trachyte of 593 

Bonneville region, saline efflorescences .......--.---- 501 

Bonpland, Mount, glaciers of .........-.-.-.------+-- 475 

Boone Creek, Truckee group, Miocene of.......----- 414 

Bosjemanite: can -eceer ees eases ear oaseneaeeceenamans 499 

Botryoidal surface of thinolite 517 

Boulder clay, absence of, in United States Cordilleras 460 

British Columbiat--c-s=----s<-ssceceue 459 

Boulder Creek, Ogden, quartzite of .........--------- 194 

Boussinpault.-sccccecsss sce e seeree cncanaaseeenans 511 

Box ‘Elder'Cation; Triassic: 522222 2sec.-ceeneseseceees 255 

Box Elder Creek, Triassic .........-.-- 251 
| Bradley, Frank H ...... 


Brewer, W. Il ...... 
Brewster, B. E.. 
BridperBasin..cevecscsescisceccccecsnacensseecoe cent. 


INDEX. T15 
Page. Page. 
Bridger Basin, general section of Bridger group in.. 400 | Cambrian and Silurian of Oquirrh Range ....- Seatac 184, 185 
Green River gronp of....-..-.....---- 388 Pifion Range ...-.-..----- 1£9, 190 
Brig PereTOUD yes e meee es sae an eee een aes Seeeeen 394, 395, 448 Roberts Peak Mountains . 191, 192 
BadeanGseeececaceeace aah comme) C(t |) (OBI) Ura eRe AS cen coceecooosbpeecc Score sscO0 EoEAeS 582, 584 
BridpersBasin@e--oseo cee ee este e aero 399, 400 | Camp Baker, Montana, Miocene of 408 
Cherokee anticlinal ...........--..--. 397 | Camp Douglas Trias ...-....--....--.--.-- 265 
Cherty Stratasee- me nentem lean =seemce 401 | \Camp Halleck, Nevada.---...<2--- 22. cose ccccnesces 590, 59L 
Church) Buttea=---<s---sense==comcca 401 | Camp Stevenson, Vermilion Creek group 369 
distribution 396 | Canon City, Jurassic reptiles......-....-.. 285 
TOTES) capes ceccosoccos 394 | Cafons, Ammonite ..-..-. 223 
fresh-water mollusks of 402 Anteros.....-.. 263 
general section of, in Bridger Basin. . 400 PANLIMON Yaensee-seniscacesiameesseaee eens eee 75, 632 
GrizziveDnitesannceanmen ccs sccenane = 401 Te EE See pcos ecedbadccr cococbesacacoad 644, 666 
Henry’s Fork.... 402 Borkshire .........- - --066, 567, 570, 571, 652 
Mount Corsonlesn=sseces- se -—- 7 e--oo= 402 Bingham....... spe RcOceosoS 213, 214 
nonconformity with Green River BRK acenceme = 642 
FEROIIO qoogrocectecoaSecqaEcEEscaeas 339 Buena Vista .... 2.2 2--c eee n essen nencnes 268, 273, 293 
Tortlepbluuseaaaneccesee==soe-=—- 402 CavG\acceceecee sence ease na aeteet een nace 660 
vertebrate fauna of .........------ 403, 104, 405 Clan Alpine... 564, 634 
Washakie Bad Lands .....-.-..--. 397, 398, 399 Clover ....... 5 69 
Wasbakie Basin 396, 397 Cottonwood .. 47 
British Columbia, bowlder clay of......---.---.----- 459 (Coyote csts=scses ea ene eeeeee seamen Q7 
general ice-cap in.....-....--..--. 459 Crmg00 22s eoe cet cosccok coe cence ee cc caseous OL 
Brown’s Park, Green River Group. -- 3e4 Day's sess ees ee = ? 635 
Bruin Peak, Archean rocks ......--.--- ...--.+----- 38 Dryecoesecoseeees . 191, 197 
Brush Creek, Colorado Cretaceous. ..-.--.----------- 316 Dau Chesne ..-. 151 
Buck Mountain, dioritic gneiss.........-...-.--.---- 41 HUST RececoceCeeccccos Coch coccubacopaaacEeos 589 
Buena Vista Cafion, Jura......------..-------------- CN Oeeecer a sees nae eineeesenees eee eee 330, 370 
Trias Egan..-.... peseeacoceeoce. Usher 
Trias, Koipato group Egyptian .... 2.222. cccces conse cncnn- 572, 573, 615, 617 
Buffalo Peak, basalt ........-.-.-.----- 1dorad0\c a2. saccanacessa- cis clscersesctes= ae 666 
Trias ..-. Emigrant .<-<....--..ccscccccccccascoee-=-- 201 
region, Truckee group, Miocene......- 414 Farmington ........2.0-¢--eccssceesseeeeeees 50, 51, 52 
BUNSEN oa) eee ae see een neon eee ade esemrcinse=—mem === 691 Garnet ...-..-. = 43 
palagonite analyses by...--...-------------- AID NG 6000. Seriecanccecwn- = cesece===-0iecneee === 145, 262 
Bunsen’s law...... 2222-0 --2--- ener ee cneees coceeeene- 78 | | Granite .........-2.02--cceecee-sceer ens nnne 71 
92, 64€, 647 
589 
Cacho la Poudre Creek, Dakota Cretaceous....-..--. 300 40 
Fox Hill Cretaceous. .....-- : 320 45, 46 
Laramie Cretaceous ..---.--- 332 : viz 
MT TIAG ten eee cana ecccaceees 255 | Moleen.........--.----++--22--2---ee eee eee 218, 224 
Cache Valley, Humboldt group....-.-.---.---------- 436 |  North.....-....20.--+----- 222 e eee eee e eee e ee 198 
Cajon Pass, Miocene .....----------+++eeseee--2-2 22: 413 82 
California, great desert...--..- Scco86 505 --- 198 
talus-slopes ..-.--.-------- Apaoseeconeece 486 218, 617, 618 
Call’s Fort, Cambrian .....--.----- geoeer Bese rissenee 178 563, 574, 588 
Cnr Dia ee ee see an eee a anne sok 000) | NNN OE SUICY 8 oon an wene come ona aoa no nec oras as 304 
Call’s Fort ...-.----..-<--+ -217, 617, 618 
Cottonwood section. .-. =-9 600 
Egan Cafion.......------ 588 
fossils 31 | Railroad ...... 0.2... ----0-e-eees ones eneeee 660 
primordial fossils, Eureka....-.----------- 129 590 
quartzite. .--..-.------.s000------0-0 0000s 156 | —« Sacramento ...-..- . 268, ae 
quartzites, Aqui Range. ..-.-..-----------+ 195,186 | | =‘ Santa Clara..--.... 27 
Ogden Caiion section...-..----- 175 Sawmill ...-- 49 
Ute Petktescsescscsssccceeevrss 179 Sheep Corral... 603, 605 
recapitulation ....-..----+-+++++++--++++--- Snake......-..- 592 
BHAIOB: so ae aciewae ce enccercee<-sscccesesce== Soldlori-.c2<ccocnacccncnccccensnsssses 213 
Schell Creek Mountains Spring .....--.--22ee eee eee eeeeee eee -- 612, 613 
slates, lower...-----. Btatiecstecsssc-jcntaqswwecesnccnnn=es.ceness 273, 276, 277 
Weber Caiion section. ‘ 157 Truckee ......- 53, 554, 565, 566, 576, 651, 677 
White Pino Range ....--..----------+----- 187 Valley .-----.-- BA ena woe ot 004, GAS 
and Silarian of Eureka mining district .-. 188, 129 Wagon ......----se0e-+---------- 558, 567, 568, 598, 66L 
Great Basin ...... ..-.---- 184 Wahaatch .........2-- --c20eceeee--e-------- 198 


776 


Page. 

Cafions, Weber . -152, 156, 157, 158, 160, 162, 163, 164, 265, 293, 369 
Willow .. 636 
Caiions, dry.....-.- 486 
extinct glaciers in -. 467 
general form of 485 

glaciel and torrent-worn compared..-..-..-- 478, 479 
post-Pliocene.........--- 2+. +22 ee eee eee eee e ee 487 
relations to the two Glacial periods .......-. 487, 488 

Uland ice cee san ater eee eee anen ae eaes 487 
TElawO0S Oliesenesosececaeeaeeeer ere 478 

Cantons and (extinct) glaciers ...--.----------++----- 467 
Carbonate lakes, Regtown, Nevada ..........------- 510 
Carvonic acid; liquid)... 22-22. cen --e= 84 
Carboniferous cherts, analysis of..... 143 
section on Coxl Creek . - 211, 212 

of Zencbia Peak = 144 

Carico Lake, rhyolite of ..-......-.-- 622, 623 
Carlin Peak, andesite, hornblendic . -. 563 
THY OMCs co csewe-aseicee S 621 

Carlin Valley, Wahsatch limestone - . 5 212 
Carlton Mine, Fox Hill Cretaceous.--.- 3 330 
Carrington Island, Wahsatch limestone ......-..--- 200 
Carr Station, Niobrara group. ...-.-...-.----eece-eee 428 
Carson lak6)-csstecsc sos eearaaeae aa eaacnenrar esas 441 
CarsomRivert.cs-cc-ocasssencsssceeseeeeae ia ceecriaas 13 
Cascade Rage’. -sse< csecseceacacss note ncweneienee 452, 453, 454 
POOLOLY i josis<ouce meisacicioesecauewacsee 452, 453 
GassianiStissssscptcesesesasedessacsscndeaseniceneee 347 
CastletPeaksnecccssccos sees cosmeat ce cnnesesinceocean= 202 
Catbedral Bluffs, Green River group of......------- 382 
G@aieasus, <-.ce nae sate ossesocwee ea casscosrsc=sccees= 10 
compared to Uinta ...-.. 10 

Causes of Archiean metamorphism 112 
Caustic contact phenomena...... . 76 
Cave Csfion, basalt. . 660 
CawelCreek:5--.<c-s5s 191 
Cave Springs, trachyte.. 595 
Cedar Mountains, andesite....... = 562 
andesite (angitic) of. .-. 571 

trachy te of. 594 

Chalk Bluffs, Miocene of..-...---.------ FOC IOCO 451 
Niobrara group Of.......ccccceccesecs 426 

White Jtiver croup of---.<-c.csnecee 409 

Chalk Creek, Colorado Cretaceous...........-------- 319 
Makota(Cretaceous ses. scree seer sees 304 

Champlain ‘Period... i <-ac es ctcccasisnesscuane 459 
character of, in Cordilleras . ...-.. 465 

difference east and west ......---. 465 

east and west comparison........ 4°6 

Champlain rivers of Cordilleras, cafion-cutting by.. 466 
Champlain subsidence, Gilbert’s views. ....-...----- 491 
Change of level of Winnemucca Lake ........-..... 505 
Chaptenih, ceocconan- os ecce eet e eee 1 
Liges 15 

Ti. 137 

LV: 249 

Vc 359 

vI 531 

VIL 545 

VIII 727 
Character of glaciation in Rocky Mountains ........ 468, 469 
Chataya Peak, Basaltiof -...2.:-..<0.cesececssceauas 664 
rhyolite of. 22.2.-2<2.s.cesecccccee ss 640 

frachyteOl Soncssces csetsaeenceeeee 600 


Chemical history of Lake Lahontan ......... 519, 520, 521, 522 


INDEX. 


Page. 
Chemical persistence of Archwan beds .-----.------ 104 
Chemical persistence and independence of individual 
beds in Archean schists ..--...------------------- 44 
Chemistry of Lake Bonneville -.....-..-----.------- 498 
Lake Humboldt 510 
Lake Lahontan, climatic deductions 
FLOM oo cos cmces oem eeseemnese == === 523 
limestone in Coal Measures . 5 131 
Pyramid Lake water.....--- - 509, 510 
Saltibakerwaterssccceese sees s eee oes 496, 497 
518 
Chemung 206 
fossils, Devonian and Upper Helderberg -. 236 
Cherokee anticlinal, Bridger group ....-.---.------- 397 
Chereokee’ Butte, Irias: 2... 222 o.- 6 eo en ceen oan 258 
Cherokee Ridge, Green River group of........-.---. 383, 384 
Cherty strata of Bridger group. ...-.---------.---- 401 
Cheyenne Lake ........----.----------+-----+--2---- 456 
Pliocene Of =. e<cowmsen nesses aaatan= 455 
Cheyenne, Niobrara group of ......----..----------- 429 
Chimney Station Palwozoic -.......-..--.----------- 211 
Chlorite, pseudomorph after garnet ......-.--..----- 105 
in muscovite gneiss in Farmington Cain, 
Woahsateht soos ssseeeen sn sescan samc cedan= SL 
Chugwater, Niobrara group of ........-.------------ 429 
EDTA SSO recs os. cah anon asenctensnnettae 253, 254 
Church Buttes, Bridger group of ......-----..--.---- 401 
Circassian beds --secio sc snslewma'= 274 
Citadel Cliff, Humboldt Pliocene of --.-. 5 438 
Citadel Peak, Raft River Mountains .---..- é 54 
City Creek Caiion, Silu:ian Ute limestone of. -- 173,174 
Clan Alpine Caiion, rhyolite of..........-- : 634 
Glark’sPeakt:c- css. sees ses 19 
altitude of .. 7 
granites of... -- 30,31 
Clark Station, basalt of 67 
Classification of volcanic rocks..........--.++-+-- 721, 722, 723 
Clay TON a cowwecee coiswen merase e see eeecieme cea 197, 198, 213 
Clayton's Peak, Archran summit of.......-..-...--- 126 
Clear Creek, cnolsses:of, 222cces-ocnce se eee see 26 
Climate, evidence of modern oscillation of .......-.- 527 
present oscillation of:.--2-5. 222-27 -coceces 526 
Glover’ Peak sa .cs.sesscecacan sceneteeestaeecaencae 475 
Cluro Hills, Archean quartzite in....-...-..--...--- 2 
THYONLO Of; cosa am ncewecdeweceeesaemen=ae 621 
Coal in Colorado Cretaceous ...........------------- 316 
Fox Hill Cretaceous. - ro 329 
Green River group... - -391, 392, 393 
Laramie Cretaceous. . 334 
Coal bed in Dakota... 303 
Coal. Creek 2a. cones sc csscasesteccss : 93 
Carboniferous section on. . oe 2115213) 
Coal Measures --....:.----.<--c<scese 129 
fOSSIS/.c2-a-enn- oe oo - 131, 202 
limestone, chemistry .......---....--- 131 
Lower (Wahsatch limestone) fossils.. 239, 240 
(Upper) Albion Peak .......-....----- 224 
Antler Peak.. men 225 
Battle Mountain. a 225 
Connor's Peak -..........--.- 221 
Cottonwood section ........-. 170, 171 
Euclid Peak.....-- LOSES IOS 223 
foRsils! tases es esse as eres 242, 243 
of Great: Basinw—---..~------—- 221 
Little Cedar Mountains ...-... 223 


INDEX. vivir, 
Page. Page. 
Coal Measures (Upper) Moleen Cafion..-.....-..----- 224 | Cortez Mountains, trachytes of .... .........--..---- 598, 599 
Moleen Peak ......- 224 | Cortez Peak, quartzose propylite of ..............558, 559, 560 
near Montello Station ..-...... 221 PHYOlt@ Of-s soeces Decssccseccccewnccee 621, 622 
Oquirrh Range........-...--. 221 | Cortez Range, andesite (angitic) of......-....-...-.. 574 
Orford Peak ..- : 223 andesite (hornblendic) of ......-...--- 563 
Ow] Valley.-........---...--- 222 Archean rocks of ......-..--..-----++ 70, 71 
Peoquop Range .--.---------- 222 basaltiofessaesice Sseceee-=” O60\60L 
Pine Mountain . 5 222 Gacite ofe ese ee ee 
recapitulation . - eo- 241,242 Granite Caiion, granite of. 
SPoaMNOME Ses ae ae a 222 granite, dioritic of.........-.---.- 
Weber Cafion section -....... 162, 163 pegmatite in granite of. 
Willow Creek ..-...=---=---.. 995 propylite|otecss asst seen seer c eee 
(Upper and Lower) fossils common to. 245 quartz of granite, fluid inclusions in.. 71, 72 
Coal mine, Spriggs ----- 317,318 quartzose propylite of....-.---..-. 557, 558, 559 
Coalville, Colorado Cretaceous 316 Thyolite of-cw eta see eeee cen eeeccans 620, 621 
Fox Hill Cretaceous. ..........-..--------- 327, 330 Tenabo Mountain, granite of .-...---. 3,7 
Vermilion Creek ....--.-.--.---++---+++--- 371 | Cottonwood Creek, rhyolite of...........--.---.----- 639 
Colorado group ------------ -----+--------- 343 region, Wabsatch, Archean geological 
Cretaceous.....------------- 305 TelAhlONS (Olea eee ee 43 
Colorado Range ..---------- 5,6 section, Coal Measures (Upper) of...--. 170, 171 
anticlinal of 21, 22 Permo-Carboniferous of ..-..-.- 171 
aplitic granite of .-..- coco ttceeeeeee 22, 23 Silurian Ute limestone of.-...-. 167, 168 
Archwan Oof......--------- -17, 18, 19, 22 Weber quartzite of.....--...--- 170 
Archwan core of.--..-- 21 | Coyote Caiion, Koipato Trias. .....-....--..--..-+-- 273 
Colorado Cretaceons of.. 305 | Crawley Butte, granite of = 37 
configuration of.....-..------------- 17,18 | Crescent Peak, andesite (hornblendic) of ....-. Sere 564 
Dakota Cretaceous of..-...--.--..--- 299 trachytes!of-.---s---4-eee-s~- 581, 582, 583, 584 
eruptive Archean rocks ....-- : 24 | Crescent Valley, saline deposit of......---..--------+ 503 
glaciers (extinct) traces of,in ...... 467 | Cretaceous, Colorado group.-.....--.---..-.------+--- 305 
QNCISKOR Of e-em -melesn asa 5 23 Bellevue Peak....-....-. 310 
granite, intrusive of........-....--- . 28 Big Thompson Creek .... 303 
STApN LO Ota eeewateas araceems aoa an 27 Brush Creek.......--.--. 316 
Jura of....... CoaSococosagcocds cObcao 285 Chalk Creek........-.--- 319 
metamorphic granite of ..........-.- 101 cosine -sesccccccoetees 316 
(Palsoz0lciOl-.sccns---ccecconacns= 132,133, 134 Coalvilles..csec-ssncccon= 316 
Ralston Creek, hematites, slaty, of... 105 Colorado Range....-.---- 305 
Triassic of 249, 250 Como\senes sate esceeere == 310, 312 
Como, Colorado Cretaceous 310, 312 Elk Mountain ........... 313 
Dakota Cretaceous. -.--..-......-........-- 20 301 PORSIGDNUa cosa scons = 309, 318, 319 
OULa OSHS c cca) ceciscesselecacecee 289 Green River Valley .-... 315 
Concrete Flateau, Vermilion Creek group of .- 5 372 Hantz Peak ...........-. 314 
Conglomerate in Weber quartzite.....-..... 149, 217 aaee ONL seesaeniscees sees 308 
Connor’s Peak, Coal Measures (Upper) .--------.---- 221 Laramie Hills ........--- 306, 307 
Weber quartzite........-..--....--. 214 Medicine Bow Range ---. 310 
Conoidal structure of granite....-. SCO SESS 110, 111 Medicine Bow Station -.- 313 
Contemporaneous geological action ....-...- - 528, 529 North Park ........-- 310, 311, 312 
Cooper Creek, Fox Hill Cretaceous .....-.-- 321 Park’s Ranch .....-..---- 303 
Cope 353, 354 Parley’s Park 319 
Cordilleras, the term -5, 106, 459, 465, 466, 472, 525 Rock Creck 310 
Archean of 533, 534 Savory Plateau ..-.....-- 313 
petrological simplicity of. 106 Sheep Butte ...........-.- 313 
character of Champlain Period in. 465 Uinta Range....-...----- 3l4 
OMIM ALC Okase eam tect atm lem ctaicteictale =i 465 Vermilion Creek......--- 3l4 
débris-slopes of (modern) ...-...---.---. 472 WWiQUSRUON cee enciscc nine 316 
general absence of terraces ---.- 466 Weber River ............ 316, 317 
geological section of... 1 Yampa Plateau.......... 315 
glaciers (extinct) of....-..--.----- 460 Dakota group ...---.--.------------+--- 298, 299 
series compared with Appalachian...... 536 Ashley C.eck ........---- 303 
source of moisture of....-...-------.---- 525 Big Thompson Creek .--. 300 
in United States, absence of bowlder clay 460 Cache la Poudre Creek .. 300 
valleys (internal), Quaternary deposit of. 460 Chalk Creck ..........--- 304 
Correlation of Archw@an rocks ......---------------- 99 Colorado Range ..-..----- 296 
Glacial periods with Flood periods of Oom0leaceee-ere-ve=--= = 301 
Lake Lahontan ....-..---. AO 2950 524 East Cafion Creck.....--. 304 
voleanic rocks ....-.....---ceeceeenee 678 Elk Mountain............ 302 


778 INDEX. 
Page. Page. 
Cretaceous, Dakota group, Laramie Hills....-..----- 299 | Cross-stratification of Trias ..................2.--2. 344 
North Park . - -- 301,302 | Crow Creek, Niobrara group of .........-....-.. 429 
Park Range...----------- 303 White River group of .......---..- 410 
Parley's Cafion.-...-.-.... 304 | Croydon, Fox Hill Cretaceous. ............-.---- 330 
Peoria .......-- : 303 | Crystalline schists, geognostic position of 118 
Red Butte Station........ 300 | Crystalline schists and granites petrologically com- 
Rocky Mountains. 299 paredsss..22it ee eee eee 117 
Uinta Range. .--.-------- 303 | Curlew Valley, basalt of ... 658 
Wahsatch......---------- 304 | Cyanite in quartzite 34 
Fort Benton fossils . --.-.- - 848 schist, Garnet Cafion, Uinta Range...... 43 
Fort Pierre... Eeee 349 
Fox Hill group... - 320, 349, 350 
Aspen voesssc-ceescences 996)|  Wacite canes cenwen seen sane ae enone eee eene ee cncene 567 
Bear River City .--..--. 325 Berkshire Cafion ... 570, 571 
Big Horn Ridge ........ 326 Cortez Range ......- - 566, 567 
Cache la Poudre Creek. . 320 Mullen’s Gap ........---..------------------- 569 
Carlton Mine.....-...-. 330 | Papoose Peak: 2. canicaecesieesoesesessence nee 567 
coal in...- - 329 | Shoshone)! Peak cceac<siccesnsiesasasceteescnas 568, 569 
Coalville -. -- 327, 330 Virginia Range. .. 569, 570, 57 
Cooper Creek.......---- 321 Wagon Canon .....- -. 567, 568 
Croydon -rescneseseseee 330 2 635 
Echo Cafion ........-..- 330 303 
Huviatile shells in ...... 329 | Dakota group..-.......---..2.-.----2---222--- eee ee 348 
Fort Steele ...-.....-... 323 | Cretaceous ............-..---.-------- 298, 299 
Four Mile Creek ...-...-. 329 | Dana, B.S ......----------------++----- +e Benacce 408, 455, 517 
fOSSilsineeeesee ee ees 328, 329 117, 191, 459, 465, 517 
Great Plains . 990 ||| Darwin, Charles)... .s-<<coses-cses cee ae esosee eee ses 711, 715 
Ham's Hill... 325 | Dawn of volcanic activity ..........-....----------- 546, 547 
Laramie Plains 01h MUSWSONN Gothen s eeee aon ee etesamaseerer 101, 103, 459, 463, 464 
Medicine Bow Station .. 922 | Davis Peak, trachyte of..............0...-2e--cs--0- 581 
Oyster Ridge ......-.... 325 | Davy, Sir Humphry, chemical theory of hypogeal 
Quaking Asp Mountain. 324 heat ~~... -++- +++ 2222+ -2e eee eee e ee cece ee ee eee eee eee 696 
Rock Creek.......------ _ 321 Dead Man’s Springs, Green River group of ......... 390 
Rock Springs . 324 Triag of ...--...-.----..e0ss0- 261 
Spriggs mine 398 | Dead Sea and Salt Lake water compared...... 55 497 
Wansit’s Ridge......... 327 | Débris of Dome Mountain, Toyabe Range .......... 481 
Witch's Rocks........-- 330 high mountain regions. ......... O 481 
Laramie) proup -<-:-----<:-5-0csee-2esee 331, 350 Himplayas (222 en-eecescneeceea== 3 482 
Bitter Creek region. .... 335, 336 PilotsPeak secs ee neateececeee seas : 421 
Block Butto....<<<scee- 336, 337 Wabsatch 481 
Cache la Poudre......-- 332 slopes (modern) of Cordilleras...-.......----- 472 
Coalaneasscen coon ees eee 334 | Deep Creek Valley, rhyolite of.........-. 
conclusions of Meek, Degradation, rapid, of mountains 
Hayden, and Lesque- peaks......... 
TONKS sees - Sse kees ee 3515|( Delabeche ecco teeaesa ones ceseeeeeeeeae 
discussion: of/age of 2... 951,352, ||Delesse----- ween een. nee ne seman 
353, 354, 355, 356, 357 | Deposits of Gosiute Lake...............-------.---+ 
EVange-ccsssseneseonces 332 Pah-Uteliak@vcoacscassesceseeeeeeaaee= 
fossil'in 2.2<.c.cescesoes 332, 333 Pliocene lakes 
Great Plains ........ 331, 332, 333 Ute Lake .... 
Hallvillotec-scectescoes 337, 338 Washakie Lake 
Laramie Plains. ........ 309\| Depression period: <--..- <2 -.2522-se~scccsaerserce== 
Lone Tree Creek ..-..-.- 332 | Desatoya Mountains, rhyolite of..........-.....-.-- 
Park's Station ...... 332, 334, 335 TRIAS 08 en ane 
‘PlatteviliGs..csessseecee 332 | Des Chutes River, Miocene of...... 
Point of Rocks .. 336 | Desert Buttes, rhyolite of........... 608 
Salt Wells......... 336 ||) Desert|Gap, rhyolite of. ----c-e~ oc nneeteeer yer ee 610 
Separation Station .. 334 | Desiccation, Lake Lahontan ...............--.....-- 511, 522 
Niobrara fossils: /..-<. s.s<-su-=<5.ccuseen 349 | Devonian, Genesee fossils.........-...-..--.-------- 237 
recapitulation:.....2..2.<cc2s+.ssceeceas 347 Ogden quartzite, Cottonwood section ---.. 163 
résumé. ....--.. ---.538, 539, 540 of Great Basin....-.--- 193 
BECtiOn Olver. cates en< cases shn aes — tee 296 Humboldt Range. --. 193 
by Meek and Hayden........ 297 Ogden Canon section... 17 
Cretaceous subdivisions ................---..--.-02+ 347,348 | Devonian, Ogden quartzite, of Pinon Range ...-..-. 190, 194 
Crooked River, Miocene of...--......-......2.-0000e 418, 423 Weber Canon section .. 157, 158 


INDEX. 


Page. 

Devonian, (Upper), Helderberg and Chemung fossils 236 
Diagnosis of Archian rocks .....-.---.------------ 117 
Diamond Mountain.... 141 
Vermilion Creek group Nore 367 

Diamond Valley, Alkali Flat 503 
Minosanriany posse) ses ees= aes - 337, 338 
Diorite dikes, Medicine Peak.....--..--..--- decsscs 34 
GH NaN ches Sean asceriias peapooreeeoapaooscas 34 
Dioritic gneiss, Buck Mountain........--.---------- 41 
Rawlings Butte. --..-.....----------- 42 
Dioritoid granite, Havallah Range.......--.---..--- 82, 83 - 
Discussion of age of Laramie Cretaceous - ------ 351, 352, 353, 
j 354, 355, 356, 357 

northern ice-cap..- 463 

Distribution of age of rhyolite ---..-. BH 606 
dacites and andesites. .- of 562 

trachytes .-...-.-.. - 578, 579 

Dixias elles grachLOOl. sae ceserciess<ocie===enleos == 597 
DixiovPass. ray tesiOleen i cweesiee< core ssese=~ == 596, 597 
Dixie Valley, Green River group of .......--....--- 392 
Dolomite; Uriasso pecs ea- neces ace aa eases 344 
Dolphin Island, Wahsatch limestone in.-..---.------ 200 
Donegal, Ireland, granite of........--..------------- 110 
Drift Onl OU been eer eee ea ee cen ale eee nam 459 
Dry Cafion, sub-Carboniferous .-..--.--..----------- 197 
Du Chesne Cafion 151 
AlBOZOIC ...- 2222-2 eee een nee - 146 

‘Triassceaee - 263, 264 

Duff Creek, basalt of . 658 
Dunn Glen, Trias .-. 279 
Dutton, C. E 698 
Dutton Creek.....- .--..- ---22-+0--2--- ee cones ven ee 309 
Dyampang-Kulon, Java, palagonite of .-.-.-.------- 417 
Eagle Lake, basalt of ......-.--------+-++--2+-ee22e+ 660 
Eagle Valley, saline efflorescences of -....---------- 502 
East Cafon Creek, Dakota Cretaceous .---.----.---- 304 
trachyteg <-2..--.--2----~0-0-==¢ 529 

Vermilion Creek group..-..----- 371 

East Mountain Palwozoic.......-------------------- 151 
East and west, differences of, in Champlain Period . 465 
Echo Cafion, Fox Hill Cretaceous ...-..------------- 330 
Vermilion Creek group of .---- 370 

Echo City, Vermilion Creek group of. .- 371 
Efflorescence of Black Rock Desert. .- 513 
Quinn’s River sink.--.. - 514 

Egan Mountains, Wahsatch limestone in . =5 203 
Egyptian Cation, augitic andesite of .--- --- 572,573 
rhyolite of ..-...-------+----+----+- 615, 617 

Ehrenberg, C. E...-.. .-----------+-+-22+-222eeeeeee- 420 
Eldorado Caton, basalt Olen enna a ae eeeerscsencinaane 606 
Elk Gap, Green River group of ...--..-------------- 325 
Elk Head Mountains, basalt of ...-.. .------------- 654, 657 
trachyte of ..........-.--- 581, 582, 583 

Elk Mountain ...........--22- 20200 ----eeeeee eee eee 19 
Altitude OL: -n--cccewinenesoceccess-===0 7 

Colorado Cretaceous. .-..-------- 313 

Dakota Cretaceous .--------.---- 302 

IMTIAG cisceeneses== cam = 258 

Elko Range, Green River group --.--- 393 
rhyolite of .--..----- 616 

Emigrant Caiion .....--..------------++----+++20+--° 201 


Emmons, §.F ..-<..-----+- 4, 303, 433, 449, 551, 572, 613, 629, 743 


Page 
EMMONS POA... amaccseaccccasensecceccscsneence ss 151 
Engelmann, Dr... 211 
Eocene, Alabama ... 360 
Bridger group. 394 
deposits... 541 
Elko, Novada .....-. 450 
general Cistribution of . 450 
SUDALVISIONS (Of2ene eset ee esaanne onan seme 360 
MOrtiARy? teesceele ea etetee ec meecsle sep alace e= = 359 
Vermilion Creek group......-.-..25...--2-- 360, 361 
OfiwestermvAmericwa 2-2 -<-a2=n—=siconaan = 359, 360 
Eocene and Laramie, relations of ......-....---.---- 444 
Erosion, the cause of fusion ....-...--.---.-- .----- 704, 705 
ane oon store Gtoste cocnccStdaoso5 479, 421 
three types of 480, 481 
Eruptive rocks, connected with post Jurassic orogra- 

TON Saat associ s Soot ne has seeocenclueseeaccaa 546 
Escalante Hills, Paleozoic of - 144 
Escalante Plateau, Trias... 261 
Hecalantanvyalleyaeeenecaseceescsaae= tieessee cso 491 
Ethel) Peak, pranite of, 232 -sen2- sens cs ceceaseea== 37 
Hina; pala fonitG. of. --<o sete = << -\aseseecacceee=== 418 
Euclid Peak, Coal Measures (Upper) of..-...------- 223 
Eureka Cambrian, primordial fossils of - - 1289 
Eureka mining district, Cambrian and Silurian. ---- 188, 189 
Evans, Laramie Cretaceous .------.--...------.----- 332 
Evanston, rhyolite near ....-..-----.-.02--..eceeee- c08 

Vermilion Creek group of .- 370 
Evaporation products of Lake Bonneville ... 498, 499 
Extinct glaciers and caiions.-...-----.--...---- 467 


Extinct glaciers and existing glaciers, their distribu. 
tion compared .--. =< 22.02 0.-5.-seccece -coeee- === 
Extinction of Gosiute Lake. 5 
Uinta Lake <<. ooo coc ee sc cscesecscces- 


Wairview beakieessccnciecersccsaricies=<s sess sisaves= 221 
Farmington Caton, Archean schists of. -- 50,51 
gooiss of.......--....2----se0--- 50 

gneiss, minerals in, change of 
their position ....-....------- 50 
Fault of Wahsatelht...22<---.2-c.- cen ccccwc cece 726 
Felsitic porphyry. .--...-..-----------++--ee-eeeee2s 24, 28 
muscovite in 28 
Fish Creek Mountains, Archwan rocks of son 80 
basalt Othesseass=-aceeceee 664 
granite of .... 20 
propylite of- -. 552 
rhyolite of .......---.-. 632, 635 
Trias of--. 281 
Fisher, Rev. O..----.----------- 698 
Flaming Gorge, Jura of .. on 290 
MT T108)OL2oscc -icecece cwse-i~= -- 259, 260 
Vermilion Creek group in .-...---- 363 
Fluviatilo shells in Fox Hill Cretaceous ...--------- 329 
Fontanelle Creek 391 
Forellen Creek.....--..--+---+---0+eeceeee cece eeenee 201 
Forman Mountain, rhyolite of .......--------------- 649 
Form of cafions in general.......--. --+--+---+-+-+++ 485 
Fort Benton group..-..-- ---------+++++++° 305 
Cretaceous fossils.-.---------- 343 
Forticth Parallel, exploration of ..-.. 2 
531 


general features of 


780 INDEX. 


Page. 

Fortieth Parallel, glaciers (extinct)of, area of distribu- 
tion in 467 
topographical methods of. . 768 
triangulation of on 764 
Fortification Peak, basalt of .-.------.-------------- 656, 657 
Vermilion Creek group. --..----- 362 
Fort Pierre group. ....-..---+---+-+-+---+-+-2ee+e0+- 305 
Cretaceous: c-csces-eccseeeeteee saree 349 
Fort Steele, Fox Hill Cretaceous -..--------.--------- 323 
Fort Union group. ....-.-.----------+2+ 2-202 eereee: 353 
White River group of ..-..----- 2 409 
Fossil fishes of Green River group..-..----- 2 394 
Fossil Hill, infusorial silica of ..---- 419, 420 
Miocene limestone of. . 422 
Fossil insects of Green River group - 394 
reptiles of Jurassic. .....-..---------++---+++-- 203 
Fossils, Acerbularia pentagona --- 206, 236 
Acrochordiceras Hyatti.....-....----------- 284 
Acropagia Utahensis.........---.--------+0- 318 
Agathaumas sylvestre.....--- Ganon shee neate 337, 376 
Agnostus commonis .........-------------- 187, 231 
IN OO0lte= cece acne ee eaee sas aneaamere 189, 231 
prolongus .........--<----ssesee-- 1€9, 231 
tUMidOSUS =Arjesacsewcngcctoe anaes 189, 231 
Agriocheerus antiquus -....-.--...--..----- 411 
PUMUNS 2a. cc comecesee ete c 407 
Aletomnis bellus=-222-5--siocsasnecesae 404 
gracilis -- 404 
nobilis ..- 404 
perpix ..... 404 
venustus... 404 


Alligator heterodon. - 
Allomys nitens .... 
Allosaurus fragilis. 


luearis - Sees 
Alveolites multiseptatus.... 
Amia depressu8...-.-...00cccece-snnasecences 
MOGs o cacam ance ace ctaaneesa=ninnn cea 
INOW DOLTIANUS) Goose ace dae et enoetaaae 
NUR TON S18) cece ce emnnae ee sees aeaiaa 
Ammonites.-..-..-...... 276, 278, 320, 324, 336, 349, 350 
IA UISSGANNS co nosaeacoe cannes sane 283 
BillinfsqNusiisccseciesskaseaceac 283 
IBIAK@I ies eceanseanaaansEamces 274, 275 
(Gymnotoceras) Blakei...-....-. 283, 284 
lObatUS! :2=<-cseecce--se-2>-0ccen 333 
Amnicola Cincinnatensis .......-..-..-..... 494 
PAMOGIO Woon ccna ca cen teases eee ee eee 336 
Amplucyon vetus ......-- 41 
angustidens. - 411 
Amynodon advenum.....- . 407 
Anchippodus minor... 404 
Anchippus brevidens . ss 443 
Ancylus. undulatus << <.5<20csicaessccasnsleece 422 
PANOMIIB 30:5l02 cce,2 Se aseig swe some seta 328, 336, 337, 338, 376 
PANOBUCITALOTNAA: sorcn/ceccceser sme estan sames 404 
Antherophagus priscus..............2....-. 394 
Apatemys bellus-................. 5 404 
ADALOSRULUS AJAX: 5 --. cc emaacieacyocssueecees 346 
PTANGIG\020%5~2ccmsecnecocs See 346 
Aquila, Dananus:~<-.c-<:-<csccssens-ssacee 430 
Arcestes Nevadensis. . 274 
Perpland cs ssereesese vo tavascienas es 274,275 | 


Archocidaris .... 
Arctomys vitus 


=. 213, 239, 244 
ee ee ecetees 430 


Page. 

Fossils, Asineops squamifrons ...--.---------+----+ = 394 

VITICONSIN = <ancanescle== : 394 

(ASTarte jeaecaeecm cman) - 290, 315 

Atlantosaurusia-accce cements 346 

immanis ... 346 

montanus .-- = 346 

Athyris Claytoni..-.-.- -- 169,237 
carbonaria 22 

incrassata. -. 225 

planosulcatus - 169, 177, 237 

ROIS Yi cecsoe sees eater: 203, 223, 243, 244 

SiNnWatA eee socc cas wieee =e easiness 209 

subquadrate -.22-. w.20---5--| o---= 198, 233 

Pir ot HC Weenie See EAGRSS Gee aaGOLASaS 131, 


134, 135, 145, 159, 169, 172, 196, 199, 202, 
203, 205, 209, 223, 224, 225, 240, 243, 245 


AUTYDA ..- 2025 se ence enn ns cosa -- 055-0 seees 192, 234 
TOticnlarisfesosn ce 192, 201, 206, 207, 210, 234, 236 
Anulopora, Sp. 2-2... ceescesscene-snceee----2- 159 
Avicula gastroides. -......-2...220.s-------- 319 
Homfravilccocesiosscs==cc--oee ane = 275 
N@DrasCana).cesccscesecenesciessmas 332 
Avicnlopecten-2-.cccccciece=ecececes sas - <0 164 
(Eumicrotis ?) Augustensis. - . 294 
catactus........-.- - 208, 237 


curtocardinalis 
Me Coyi.- 
occidanens . 


. 173, 245 
. 164.173 
.. 164, 245 
.. 173,245 

. 173, 246 


Axinea 321 
Wyomingensis .........-..---------- 32k 
Baculitesis-ss<ecccesss 323, 324, 327, 349 
ovatus 306, 309, 311 
Bakevellia parva .....-.--.----------+++----- 146 


Baptemys Wyomingensis 
Bathyurus Pogovipensis 
Belemnites-254--. 2. cess ccsnce se sesansison ses 


CEDARS aR paba saeecicd 285, 289, 291, 292 
Nevadensis .......-----+--++----- 294 
Bellerophon..........-..-..------185, 143, 144, 145, 206 
Garbonaria:snsce-s-ctsa es 142, 145, 243, 244 

INRIBUS Stonenseves eee see senses oe 237 

Bison: Alonix. csoscc.--senecces <decesomane=<= 430, 494 
Boavus agilis ..... 405 
brevis. .... 405 
occidentalis . 5 405 

Beena arenosa..-....- 3 404 
Brontotherium gigas - = 412 
ingens . se 41L 

Bubo leptosteus. ..: . 404 
Coelospira ....-.-.- 192 
Calamodon simplex . = 377 
CRMaTrophorisi. cscce-eses (eos aenisweasaae anal 205 
Campophyllomisc. occ seneeeenaeeenaae 192, 226, 234 
Camptonectes bellistriatus........---------- 290, 291 
(eR ig nespodoseeocsecs Jacubossesese-c 430 
COMOYATIOB. -coccen aes eee asea eee 430 
Cardiomorpha Missouriensis .......-----.--- 240, 244 
Cardium 's222-0-0s-tcceseacceaess 315, 319, 324, 328, 329 
BPCCLOSMM< soca enone eee eeeionen 332 
BuDCurtuM 2 -<-. aporea saa sac eneeee 318 
CarnifexsBinneyit..... se eee ee ee ens 422 
‘Troyoni owas 422 
Cagcinium (32322 ..22-<-2 ses pea eeaonasseees 221 


INDEX. 781 


Page. Page. 

Toasils, Ceravrus.-.-...--.-- ae 233 | Fossils, Dikellocephalus.........--.-..-------------- 185 
Ceratites Haidingeri . -. 283, 278 ibilobatus®:.2---sesece--=---- 189, 231 
Ceratodus Gtintheri ...............2--ceee-- 346 Aapelliloreneaaaacecemasee a= 187, 231 
CoervusiWiarrenins--eccss ere ase neniem eee a== 430 POMNCUS Soca ericne esses = 178, 223 
Chtetes essen ata eer -202, 209, 224 MUMINCINCtUS == -essecce-e =e 18y, 231 
Chariocephalus tumifrons -...- =. 187,231 Wahsatchensis.......-...-.. 178, 223 
@hemmnitzin) ceca ean e sean eae ee 283, 291 qnadraceps ... ..-....--. 180, 187, 235 
Chonetes granulifera.146, 158, 198, 199, 205, 259, 242, 245 Dinictisdolinae--c-2-eeseese=-aseom conan s 411 
Loganensis 177, 237 Dinoceraswacustws -aescesestee-=sieaeaccene 403 
Cladopornteces-ece os em-=--=-1<- - 192, 211, 234 HNO locconuaadociicassaoono 26s 403 
prolifica 206, 207, 236 JT pee easecosacsescadsecn 403 

Clastes glaber 76 MTS DU Oleeacceece=enisseeeeaiesea== 403 
Clupea alta ... 394 DIN GRAD Rea atcles ens cleqe eo -eee == eee n a= 353, 354 
humilis - 394 Diphyphyliumiencscsncecssteseee sama mens 169, 192, 234 
UB Weeew eee none eseeee sence ase 394 fanciculum|. .cossescasnsiena=== 207, 236 
Collospitstes eee esas ee =e ase =e 234 UOMCR oe eeereseseerseeeates 206 
Conocephalites subcoronatus.-....-..-------- 180, 233 subcespitosum .....---------- 208 
Pterocephalus -. ees 187 Diplacodon elatus....................-..2..- 407 
(Pterocephalus) Jaticepas. --- 231 Diplosaurusitelix-cocecteqqem cee -=-=ee enna 346 

(Ptychoparia) Kingi-.-....-. 231 Diplocynodus stenops.....-----.------------ 77 

Corbiculajse-css soot eee eee 336, 337, 338, 373, 376 Miscena somos ee ene cate saeeesses 145, 172, 223, 294 
crassateliformis......--..--.------- 337 Drepanodon intrepidus 4i1 

fractarsccsen ee sires see scree e==—r 337 primevus 411 
Corbulaeessesceseeons -318,330, 337, 373, 376 Dromocyon vorax.......-.....----- E 403 
Coryphodon se scaseisesceas=-nase==- 367, 368, 370, 373 Dryolestes priscus .. 346 
elephantopus .........- --...--- 377 Dryptodon crassus 77 

latidens 377 Ectoganus gliriformis.-........--..----.----- 377 

radians... 377 Edmondia Pinonensis. - 210 
(Cosoryxee-seeeeeree ae a 439 Elotherium bathrodon .-...--.....-. 41L 
PUTO AE) SeqgoscanecHoe sso SuBnSooaae 430 crassum - 411 
Creosaurus atroxsesco-ce~ era o-<--\esn es ose 346 Mortoni 411 
Crinoids 33 170 SUDSRDOM eeeseesieneaeraenaseeeee 411 
Crepicephalus (Bathyurus) angulatus ....--. 187, 231 Emys euthnetus .-.-.-.-.--.--.--..--.------ 376 
Mopanellustessseese cece , 187 MOP AU AK ee eniwc ce meinneenwine sna == 376 

(Loganellus) anytus oc 261 pachylomus ....--.--..-- 5 376 

granulosus ....... 189, 231 Endiagogus saxatilis Sud 

Haguel:...<----6- 187, 231 Endiscoceras Gabbi-.----.----- 274 

maculosus ...--.-- 189, 231 Entomacodon angustidens.--...-- ---.------ 403 

nitidus - 189, 231 VASUSneonosseeeana ee entaaiaton 403 

quadrans .. . 187, 233 Entomoceras Laubei - 284 

simulator -.- - 189, 231 Eohippus 373 

unisulcatus ....... 189, 231 angustidens.... 377 

Crocodilus brevicollis... ....----..--------- 405 * cuspidatus ....--.--.--..----+----- 377 
Elliotti...---<+----2-- = 405 MA OLPen eens eee ee ee ceeeen ane 377 

grypus * 377 Derineesseesen tas A 377 

heterodon . E $77 tapirinus. 377 
Cryptonella tes eseees-nesnosenseseees 169, 201, 234, 236 validus .-. 377 
Rensellarias-s-2--/---s-oeeeeee= 206 Epihippus gracilis 407 

Cucullwa Haguei ....-.-..---- aes 293 Wintensis|asa-scessa--asceseensues 407 
Cyathophyllum Palmeri. ..-.-.....---------- 236 Eporeodon bullatas .......---.------++++-+-- 411 
(Campophyllum) Nevadensis 181, MAJOr....-.---------------- eee ee 411 

239, 244 occidentalis . 424 

Cyronatectnesseer ese aneeseeem=-eeeearineeans 337, 376 superbus ..... 424 
Garlotoniseet te eesoe eee 328 Erismatopterus Reckseckeri . 394 
Cyrtoceras cessator ......--.-------------0+- 240 Esthonyx bisulcatus ...........---------.--- 377 
Cyrtolites sinuatus. . ..-. ..- 188, 233 Eulima chrysalis..........--..2..2..2-..20-- 323 
Dalmanivgeossscsecseoseetnesse eoescsee once 216 funiculus ...-. 318 
Dentalium Meekianum........-....--------+ 202 inconspicua...- 329 
Dermatemys costilatus...--.-.-------------- 377 Eumetria punctulifera ...........200, 209, 224, 243, 244 
Diceratherium annectens.......-..--.------- 424 Tope tobe ii ee Se = Se ne ae a 290 
ATMALOM 22.22. cee ce cece sece 424 curta . 292 

CTASSUM «~~. .--0e eee eee e ee : 424 Eumicrotis Hawni.. . 173, 246 
Diceratherium nanum........----.---------. 424 Eumys elegans... a 412 
Diconodon montanus............------------ 412 MOM PHALUS ens aceisessacucesqeecnkanwawsams 146, 169 


Dicotyles hespoerius..........-.----++---0--0 443 NALOS coceeeccstetcetasscccaswte 177 


782 


INDEX. 


Page. 

Fossils, Euomphalus latus var. laxus .. - 197, 238 
Ophirensis ......... . 197, 238 
(Raphistoma) rotuliformis...--. 180 

trochiscus .....-. 180, 233 

Utahensis...<..2.20.2225 169, 177, 197, 237 

Favosites ...... Sesser ecco ceceeene ---- 192, 207, 211 
Helderbergia:-..-< ce. c-csescsecee 234 
‘polyMOrphiiisesacocesaseessscene = 236 
Wonestellaccces-soes sees -eesesen eee aes 198, 202, 238 
TQS TERT oh Pe a Seen Sec Hee Seer 142 
cylindrica .. - -205, 226, 242, 243 
Fusispira compacta ......- ae 233 
Fusus (Neptunea?) Gabbi-. 318 


Utabensis . c 
Gallionella ....--.-- f 421 


granulata . 420 
sculpta.... 420 
Geomysibisuleatus:...cscs.sececss cect oecea= 430 
Glanconome co... ==.ceea wenaasas aeteweeme 238 
Glyptosanrus princeps «22 -<ceoceee once scecee 405 
Goniatites* Kinetic. ctececncscies «eceosen 208, 240, 245 
TB VIdOVSntSicoeecs cece aeoe 274, 278, 283 
Goniobasis ..... 336, 337, 363, 366, 368, 376, 382, 385, 386, 
389, 390, 447 
Meo Carter: sqacscss eee sore seencuas 383 
nodulifera;so--asecseeneens cease 383 
TONCLG) 32: acess eases casnemosees 383, 402 
Gracnlus}Idalioeisis!:— 2 .c22scc.cecaccecees 443 
GrusHaydeni.2s---- == c-enataceecsncoecees 430 
Gryphea.....-.- b 294 
CAICGOlA seceeccsese aes seasee eee 291, 292 
Gymnotoceras Blakei. . 27 
Gyrodes depressa. ..- 319 
Halobia (Daonella) Lomelli .............-.-- 283 
SE ie Cee Se ae 274, 275, 278, 281, 283 
Helaletes boops: .--..- 22... .2c2--eccevesese 404 
BIO PUlATIS coe acces sew cs cuue ses s=ns 376 
Holiobatis radians 22.2 soc so. ac acscccncecesse 394 
Helotivasilentis(c<scs.cacscacacseucees=== 404 
Homacodon vagais ; ....-.0..cceccescesesnes 404 
Hyrachyus agrarius. ........-ccccscsesessens 404 
BairdianusS. ...2.+cccescnctscesae 404 
Hysnodon)crncians:< 2. --cccessscaressseccs 411 
CLUONtUS a steancancese eae daace ne 411 
horridus ... . 411 
Hybemys arenarius. ..-.-- 5 404 
Hyopotamus Americanus. = 411 
Hyopsodus gracilis .... BROS 407 
minusculas 403 
Hypamia elegans ...... 405 
Hystrix venustus. . 430 
Tetons Dakotensis:cerecas cease cceeeemeessiaee * 412 
TenAnaVUSVOXIIS¥ oo.ccososen eae senaee sees 405 
Illenus 192, 234 
Inoceramus.....--.-. 312, 313, 314, 323, 324, 327, 329, 350 
EA pe cee poaeeric See coac 313 
Barabini......... 307, 309, 311, 320, 324, 349 
GGlormissc<aseeiseststessascee 307, 309, 349 
Ellioti .-. Sviemwacc ueeem oa uuarte 315 
problematicus 307, 309, 310, 
318, 319, 326, 328, 330, 348 
Ischyromys typus 412 
RONG de eae soem oases = cess eaceseceetnes 206, 237 
PCULOPPING Geen eaten ssccnaseeseeeaedseeeee 185, 233 
IMiNOBSIMA..-acceswonseconseane 189, 231 


Page. 

Fossils, Laosaurns celer. . 346 
gracilis .. 346 
Laopithecus robustus.....- 411 
Leiorbynebus quadricostatus. . -- 208, 237 
Lemuravus distans .........-. : 403 
Lepidodendron......- : 238 
Lepidosteus glaber. =. sseccos--/-+-se=ae eee = 405 
IWitn OVileaasceecenenee ee aa ae 405 

Leptmna melita: ..c-<ccecs- oneseessaceene as 189, 233 
Leptarchis) primussecs.aoesea-siasceeweces ase 430 
Leptauchenia major. ~.---------=--=-.......- 411 
LeptictissHaydeniiees.--.s2-sessr-ceacccens 412 
Leptocardia carditoidea. oes 294 
typica ...=... as 294 
Leptocheerus spectabilis 7 411 
Leptomeryx Evansii...... 5 411 
Lima (Clenvides) Gabbi . = 284 
(Limatula) erecta. A 284 

VMN Datoescirsseee=cieses ieee) 436 
desodiosare-cccce.-seecscctescresine 494 
GLimnooyou wipariuss-.s-<csc-caenacesnessees 403 
Limnofelis ferox....-....-... =n aisvieeshaa'sin'sle 403 
Limnopbis crassus 405 
Limnesaurus ziphodon............---------- 405 
Limnotherium elegans...........4.---.----- 403 
tyrannus........... an 403 

Lingulepis -- 185, 233 
a. -- 178, 233 

Mera -187, 189, 231 

minuta . -- 189, 231 


Linulicardia fragosa .. -- 208, 237 


Lithophis Sargentii... 405 
Tithostrowon sence ssacecesioenase= ans 146, 181, 239, 245 
242 

Lopbophyllum proliferum..............----- 239, 244 
DUCing ss. Seccce sewnc ews e- aes ewserasenwesios 315, 318 
Maclorea- minima <<: 2 c.cs 2 cccccccccee cen’ 180, 233 
IMACTOGON cease ec eee eee ae tenieeaametet 146, 318, 320 
fey Hqeeroonccaceeecteace oocbecdeac 146 

Mactia altas.csseces- co cee snes setteeoas 335 
Warreniana 332 


Martesia. . a6 318 
Martinia lineata . 146, 147, 159, 199, 213, 240, 243, 245, 412 
Meekella striocostata c= -- 145, 242, 244 
Megalomeryx Nicbrarensis .......----------- 430 


Melania...--<cce-eessesee . 361, 365, 368, 383, 385 
BSCUIPULGE cewceccoscoc seems cones 422 
pubscolptilisscacs seo eeeeesere eee 422 

Melam pusis-ssecee a sncccmacwaes eee ecmenee 318 

antiquus 329 

Meniscotherium chamense 376 

Menodus giganteus ........-.ss-.2+-ceses--0 41 

‘Merichippas insignis) -ss<c. soo c~ see =e 430, 439 

Merycbyus clegans -...- 2.5... -4.5<.%<.sccee 430 

Merycocherus proprius......-----.--.----+: 411 

Mesohippus celer ............-.s.2206 : 412 

Boirdi scene seereenecete 412 

Michelina. <-=-<- <<<: -. 197, 237 

Mileagris antiquus. - 42 

Miohippus anceps. ..-- 424 

annectens. - 424 
Condoni...- 424 
Modiomorphe alata .......--.-..-.--...2.262 TA 
OVOAtesenn cae enceeccesicecae 274 


Modiola multilinigera ..................2000- 318 


INDEX. 


Page 
Fossils, Modiolopsis (Modiomorpha?) lata........... 284 
ovata....-.... 283 
Monotis subcircularis..............-..-..--- 275 
Montlivaltea 294 
Moropusjelatus)-<. ies acsieceouaeiecaeacne=s 430 
CIStans ye ceemecs see ceneenereremes 424 
BONOK. 2... sc cccewuscesccccvccccscs 424 
Morossurusim par sen -escinnseeecinecdee closeness 345 
Morotherium gigas -. 443 
leptonyx - 443 
Myalina ............. 146 
MS Die naian 146 
aviculoides. - : 173 
POLMIANA). <-> -2a2-ss\csecsn ess cess: 173, 246 
IM VOcltes Sees ee aan eeeeen an aaa seee cae 283 
RVICUIOIdeS) ~saseae erase’ sossscsss 5. 246 
INCONEPICUUA)— sae aSere =. cosas 246 
(Panopxa) Humboldtensis .......-. 275 
subcompressa........--.-.---..-.- 293 
Wreberensis\.2-.-- <== scscoscosce ee 164, 246 
Myophoria lineata ............------...----- 291, 293 
Mys0psiminimusSnccccsdacccccescconseseseee 404 
Naiadites ...-. -144, 243, 244 
Nanosaurus agilis....................------- 346 
INatiCarae ten oaaneccoeasareceensicsssemncece = 138 
lelinvcesinacsantceascattreas cose ooo ee 137 
Naticopaisi-co--cccesecceseseccecasace 206, 236, 240, 244 
INADUIUS sesccetentasesaeniacnscece ssn ces 275, 278, 282 
Neritellatoecnasseceee cereaes coomoScaadasoes 291 
Neritina Bannesteri .........-....-..22...-- 328 
(Dostia?) bellatula..............--. 328 
carditiformis ..........--. 328 
: 318 
te 142 
- -142, 243, 244 
. 144, 243, 244 
Nuculites triangulatus..............--..---.- 208, 237 
Nyctilestes serotinus..... 403 
Nyctitherium priscus. - 403 
VOLO ste weasese ss aencane ance 403 
Qhbolellasessseess sea e nae aeeeaane ose 187, 231, 233 
CIRCOID See een eee a ee eae a 189, 231 
Odontobasisiessnsc5-neceeese= eee aeeatane ens 338 
OBy2iGtcocesececesienre ac <-onccomnennanenns 185 
FEET LI) EY osnccccenScUCnCe cCOUnOnKCRonES 125 
ParabolOldgus se. nonsense eee 233 
prodncta....---..-----.-..-2<. saskces 185, 233 


Ophileta complanata - --- 180, 233 
Oreodon Culbertsoni - = 411 

gracilis ..... 4\1 
Oreosaurus lentus..--.-. 2.2.2 - 2s scenes eee 405 
Orocyon latidens. - - 403 
Orohippusigilishense-ssecececcecescoeenes= 404 


VASACCIGNSIS| occas asmen asics = seems 
Orteoglossum encaustum....-.-..---.------- 394 
Orthishes=seaqacseep ee ese a 192, 201, 206, 210, 234 

ONrbonarid..----- esssen scene 144, 225, 242, 243 
multistriata 201, 234 

OD Ntaieseence coco eeetinecstes= ane ee== 210 
Pogonipensis .........--..----.------ 183,233 
TOSUPiNGta .<-...<..ccce enw ~~ =~ see- 197, 238 
Orthoceras) sp.?.--0-- 0 --.se~---a55~-5 135, 145, 207, 237 
Blakei ......... 274, 233 


cossator..-..- 208 
crebrosum 144, 243, 244 


Fossils, Orthoceras Kingii 


785 


Page. 
236 
Ostrea -.. - . .290, 291, 310, 311, 323, 329, 332, 336, 337, 338, 
352, 376 


congesta .............. 306, 309, 313, 314, 348, 349 
Boleniscaesesensascee= eas 318, 325, 326, 328, 329 
Oxyeena forcipata ---- 2 -onocewiewccsan ees 376 
376 

Pachywenn ossittapaonaccseseneecosssseeaces 376 
Paleocastor Nebrascensis. 4 412 
Palseacodon yerus. ....-... . 403 
vagus -. - 403 

Paleolagus Haydeni .......... 412 
Palwosyops paludosus..-...-. 404 
Pappichthysplicatus) --<-2.--.--s-cc-+-sees 405 
Paracyclas peroccidens. .............-.2.2.<- 206, 237 
Paradoxides Nevadensis ...........-...----- 231 
Parahyos Vacane oan .c cas ceeesscsace===== 377 
(Raramys|delicatnsiss--.casaactsces=saneceee 404 
Passalacodon littoralis .. 403 
IPecteneesaaeseewiessone 2 294 
Clevelandicus . : 245 
doformis paenensses eae en eee ee ece sees 283 
Pentacrinus asteriscus .........-..-.. 263, 280, 289, 291 
POULRMORIS Socneseeecaciccissnnssmceeecioaas 206, 207, 236 
galoatusiecaccsepaseonecenceesa== 192, 237 

Perchmrug! propusl-s.ccncsecsccevesecssasena 411 
Phenacodus primevus...............-2..-6- 76 
Phareodus acnlus:.-s2---j.s0>aciese nese enasese 405 
Physa Bridgeronsis .-.........0...---scccee = 402 
Phy tolethariay on-nessesceeesesasececan=neoe 420 
Pinnubaria invequalis. 421 
Planorbis -....-- 509 
spectabilis .. 402 
Plastomenus communis . 377 
Platygonus Condoni .. 443 
BUMAQUS Socese en seeasmeneeesaaee 430 
Plenrovomanis ee <n-c1s sees accadenciccna=e 142, 207, 237 
Plenrophorus eel sesnaee esac oss ese = ae 146 
ODIODPUS ie cecssacencaseeseae= 137, 243 
Pliohipposmernixcs-cssrcereseesecoseeecesee 430 
TOD USGS ee ecoa sae ae aan ee 430 
Poebrotherium Wilsoni . 411 
Polygastera == 420 
Polypora.....-....- 198, 213, 238 
Pomatiopsis lustrica . : cA 494 
Porambouites obscurus - 188, 233 
Posidonomya fragosa .......-.--.-----s----+ 237 
Gi sos eee ea peseceeroasscss 274, 275 

Prionocyelas Woolgari...<.- 2... o-oo ne enne 348 
Procamelus robnstus........-.-.------------ 430 
Prodnctus tcceseeeosseeeeceeeea ---137, 177, 209, 237 
COLA (ena anc ancien se 131, 134, 135, 181, 239, 244 

COStQLUS = ceeccccscncmeco=s 135, 200, 205, 209 

elegans 198, 238 

Flemingi, var. Burlingtonensis .-. 198, 238 
levicostatus 198, 238 
longispinus . ......199, 205, 209, 223, 242, 244 

MUTA WINGS) sessuuiscses<s-an == 203, 242 


Nebrascensis - ...169, 199, 209, 205, 209, 221, 
222, 223, 239, 243, 245 

NGVIOGUSIB essen eases ——e =e 203 
pertenuis ............--------- 169, 239, 244 
prattenianus. . ...131, 135, 142, 159, 162, 170, 
196, 208, 209, 224, 225, 239, 243, 245 

punctatus ......-.. ~~. 181, 223, 243, 244, 245 


784 


INDEX. 


Page. 


‘Fossils; broductus:ocersi:.<.-.-1.2-0- cero cece se ces 221 


semireticulatus ..131], 133, 135, 147, 170, 172, 
198, 200, 203, 205, 203, 209, 
223, 225, 238, 239, 243, 245 


subaculeatus .......-....-. 206, 207,211, 236 
Sub-horridug|sco-c.22se-eaceee 203, 225, 244 
symmetricus...... 159, 169, 225, 239, 243, 245 
Proctus: Lofanensis. 2... ccseeeaeciacaseecees 177. 238 
PCLOCCIVENS:2ecescceaaasa se ceees 177, 197, 238 
(Protohippus:avus we esseese= ee nace eae enna 443 
PaALVulUuss sees soase cece aeeaeas 430 
DELdituse cena secee eseee nares 430, 439 
Dlacidusicescosssceencaseeeeeees 430 
supremus .- 430 
Protomerys Hallii.. 411 
Pseudomonotis...... 202 
radialis .. 202 
Pteria (avicula)....... 53 283 
Pterinea =. 207, 237 
5 ae 187 
pustulosus =... csc ccnrocecs 187, 188, 231 
Ptychophyllum infundibulum............... 206, 236 
Pupaheidyitesessc-es22scececes sere semaseee 402 
Pyrgnlifera:. soFinocsrascensnse teens ceaseee 373 
Raphistoma acuta........... eieeaeionje=siaae 180, 188, 233 
Rensellmriaisc-= 2-2 -case ccsceneenas eae eee 236 
Rhineastes:raduludsj-.5<c5c ence deansesececs 405 
Rhinoceros Nebrascensis........---......-.. 412 
occidentalis\c.ssss--ceaveece on se 412 
Oregonensis: <2 --< cu sceseeuo-esee 443 
Pacificus 424 
Rhynchonella........ 192, 210, 233, 234, 240, 274, 276 
ICMMONGlis ces sccosessesmect 206, 207, 236 
gnathophora . 291 
lingulata ... Sf 275 
Osagensis.-.. -<:--s2.. --198, 240, 244 
pustulosa .-.......... - -177, 197, 237 
Wtalisconenassscceasrassvatee =e eiar ae’ 
Saniva ensidens.........-..........0 F 405 
Scaphites ovatus ...... 309 
Warrenensis 318 
Schizodusicurtug -s--s20,.-eseacnsseceasece 144, 243, 244 
Ovata 0502.5 sete ek ee 164, 246 
Sciuravus nitidus!vscuac--0-ssseseeseeeee ee 404 
Sedgwickia concava ............. SeDrep 1 173, 243, 244 
Sindpa TOpax...- <6 ccaceseaeaaceceseces cocees 403 
Smithia‘Hennahil -:.-....cssccencss oes canes 7, 236 
Sphawra Whitneyi..-. 274 
Spharam Idahoense ... 422 
TU PORUMS oa srescereseeasete eceanos 422 
Spirifer Albapinensis .. -177, 197, 236, 237 
CAMEFAtUS...665<0.0s 0. scan eoseeces 169, 172, 
202, 209, 223, 225, 240, 243, 245 

CYOSSUB. o.oo c os cenussedescieees cons 22. 
Old Vic ecer=sesccccos coe seaeseee eee 198 
Jineatus-sensececea cosaeeneces seas 144, 169 
OPIMUS: = Sc ecscrccencctcnccee 144, 159, 196, 198 
PifioNeN sl Aen acct evese ce daaasasosne 210 
planoconvexus eee 169, 209 
pulchra ... - - 203, 221, 222, 226, 243 
setiger .. ee 198 
striatus . 2 198 
strigosus .. Z 211 
Utahensis .............. = 211 


Wanuxemi- cnc ce-scesecea tee cece 201, 234 


Page. 

Fossils; Spirifera: ---..2<ssess 2 eeeee 170, 206, 208, 210, 211, 280 
BG Son oes ne eee eee ee 280 
algentaria -ccsces-sneceeeeee cones 206, 236 
centronatajss---csecaeseesee 132, 177, 197, 237 
Engelmannit@-{-222--.. <2 ee 207, 211, 236 
Hom frayit-o.< 3-25-sesseet ence ee 275, 283 
Keokuk ... 52 233 
octoplicata. ..... -- 243, 244 
Rockymontana . -209, 243, 245 
F2)9 y FE eS SEO 2S 238 
Spiriferina Kentuckensis. 145, 159, 162, 202, 240, 243, 245 
pulchras=2s:5---ses-eeeeeeoe sees 147, 244 
BPiNOsaen-s cer see ea teeee 5 209 
Spongolithis acicularis 420, 421 
Stegosaurus armatus........-....2222eesece 346 
Streptorhynchus - 2. <2. <c-ccesesaseuenecennes 196, 208 
crassus. ......-.209, 225, 239, 242, 245 
crenistrias..seceeseeaee 208, 239, 244 
equivalyisi--os--<csee====— 237 
ineQualistasnsceasseeeae— = 177 

inflatus - 
robusta... -198, 239, 242, 245 
Strophodonta -.......- 192, 210 
Canace....-.. 206, 236 
punctulifera ... 234 
Strophomena Nemia ....... 188, 233 
rhomboidalis....... -- 197, 237 
Stylinodon mirus ....-.....-..... 404 
Succinea lineata <--.-s2.0-cs-ssesecsscaceees 494 
Syringopora.......-.-.-. messanccoctcescoeses 145, 169 
Maclurii<-s--.co-ss2-seseees 207, 224, 236 
multattenuata ...... 146, 205, 239, 242, 245 
Tachymys lucarigoce-<css-s-coseseeee-enenee 404 
Talpavus nitidus...... eiseecanie nse ciaiaaae 403 
Tancredia Warreniana 289 
Tapiravus rarus. ...... 430 
Telling s2— ess 319 
Tellinideshscccessssseeeae 2 383 
Perebratulas----tesssecaseneee 209, 283 
Augustalsescsersccesace 294 
bovidens)<---.osseee anes) - 159, 240 
Humboldtensis ..............-.. 275 
(Utahteccacscesconcenca ersaoncens 237 
Utahensis\<- cscs cscescisccseancs 169 
Testudinata -225----hssee tee oeee secon eee eees 399 
Thinohyusilentus'*—<2-s-scessacecen en eeecee 424 
ee BU eases sgeccicagos weceaee 424 
Thinosaurus leptodus. 405 
Tillomys senex..- 404 
Tillotherium fodiens .... 404 
hyracoides .. 404 
Tinoceras anceps..-.-...-. 403 
Trachyceras Judicarium ............. 274 
E 274 
jWhitnoyl--:----..-----= - 274, 278 
Trapezium........... seosotone 319 
Trematopora --- 192, 198, 202, 234 
Trigonia : 291 
quadrangularis .............0+..e0. 289 
Trionyx) puttatusaic os. -pacasseeneseeceeneee 404 
leptomitus 2s. -sse= 2 soars eeeeeaene 377 
radulug \so--6-s-- ecco ce nes een oe 377 
scutumantiquum ............ cote 376 
Trypodendron impressus..-...-......---.---- 394 
Turritella Coalvillensis .-................--- 318 


INDEX. 785 
Page. Page. 
Fossils, Turritella spironema................--.----- 329 | Geological action, contemporaneous....-..--...----- 528, 529 
Wintacyon\edax:-2-< 5 -ccces ease seeeceees 403 age, volcanic rocks of ....--..-..---- 691, 692, 693 
Uintatherium robustum............-..------ 403 connection of trachytes ........-..-..-.. 579, 580 
404 distribution of Niobrara group .-- 425 
UMidses se cseeceene - 328, 337, 365, 368, 373, 383, 403, 447 relations of middle Nevada ..... 615 
Hay deniigeesca-eeema seen etese == aan 402 section of Cordilleran system ... = 1 
Viviparus ....... 363, 365, 368, 373, 376, 383, 385, 389, 447 | Geology of Cascade Range......--...--...---------- 452, 453 
paludinzformis..........--..-.--. 402 Medicine Bow Range .....-..-.-.- bowesse 28, 29, 30 
Wyomingensis 402 Palwozoic series ....-...--.---- - 534, 535 
Q91 White River group .............- - -408, 409, 410 
293 | Gilbert, G. K........ 445, 466, 490, 491, 492, 493, 523, 525, 548, 580, 
403 581, 633, 735, 746, 749 
Zaphrentis..... Asonsagracasat 146, 169, 170, 197, 208, 219 his deductions from Bonneville beds - . - . 523 
excentrica .....2-.--.----- 181, 238, 239, 244 his theory of champlain subsidence . 491 
Stansburyi 158, 181, 225, 239, 242,245 | Gilbert's Meadows, Palzozoic. 150 
Fossils of Alpine Trias, Pi-Ute Range.....-......--- oh Gulberte Pea kiers-sa-s==seneceeeaee aaa on 151 
Coal Measures (Upper) ----.---- Jes S0cRoRb5 242,243 | Glacial age moister than the present...-.-...-...--- 524, 525 
Colorado Cretaceous ................----- 309, 318, 319 canons character Of... see. --a~=--aieaenes 473 
common to Upper and Lower Coal Measures. 245 OXCavatlONOlsecceccecco ser eniscs sian 482, 483 
Lower Helderberg 191 OTOSLONL soca 1ose cetoaee ue ceckn ccjsanewslon- sees 470, 471 
Lake Lahontan ....- 3A 509 Winta Ran gerce-tre-- se 5 . 470,471 
Laramie Cretaceous.........--...--:--.----- 332, 333 lake basins, original dryness of .....-..----- 489 
in Lower Coal Measures, but not in Upper .. 244, 245 post-Pliocene formation of ..... 488, 489 
Permo-Carboniferous .......----.----------- 245, 246 Period, cause of...... .--.-..----- eppSSDOLSCS 464 
Quebec and Lower Helderberg ...--..-----.- 192 dakestofieenes- ese en ences S809 488 
in Upper Coal Measures, but not in Lower... 243, 244 snow-distribution of .-.... 477 
Fountain Head Hills, rhyolite................--.--.. 610 subdivisions of ......-.-..-- 459 
Four Mile Creek, Fox Hill Cretaceous. - : 321 transported material of...-.-...-.- 483 
Fox Hill fossils, Cretaceous -.........--....--.------ 328, 329 ‘Periods, difficulty of distinguishing hetwenn 461 
group, Cretaceous ...........-...--..--. 320, 349, 350 two, their relation to caiions ....-... 487, 488 
Franklin Buttes, Archwan ........--- é 62 and torrent-worn caiions, their differences... 478, 479 
syenitic granite. .....- : 62 | Glaciation, freshness of, in Uinta Range ...-- 470 
Mranklinslake---~0--------s----= weenes 475 of Rocky Mountains, character of....... 468, 469 
Frémont, John C......---.--------+--+-++-+--0222e0+ 1 | Glaciers, Alpine, work of ........-....--.-------+-+- 483 
Frémont Island ......----.--.---.---------+--+------- 196 (extinct) area of, distribution in the For- 
Frémont’s Pass ...-...-..-------------- - 193, 203 tieth Parallellares\.<-2-0-----0------5~- 467 
French Creek, muscovite slates of. 34, 35 (existing), discovery of...--....--..---.--- 462 
Fresh-water mollusks of Vermilion Creek group... 373 (extinct), distribution of..--.....------.-- 460 
Fritsche ....--...-------seee22 eee eee ee ee ees n eee eee Sil (existing), distribution compared to extinct 
Fusion, erosion the cause of..-.....-..-.------------ 704, 705 ‘elnciera |e Sve ese sacs cece se obeeseceeeees 462, 463 
of volcanio rocks. .....-..-----------++++---- 696 (extinct), distribution and recession of... 461 
Granite Springs Range.......--. 476 
Humboldt Range 475, 476 
Gabby We Mo.sensess seoees cette seeeces cass wanes 275, 279, 450 Lake Marian ..--..------+----+---+-e-0000+ ae 
(COR ree io ete | i er. eee 24,27 (extinct), Little Cottonwood . 474 
Gale, L. D., analysis of Salt Lake water ee 07 Iooall (extinct) over Cordilleras\------------ Ay 
Gardner: James Uo o-2222-<2c2-s25=-0oec0sccesescess 20 lowest descent of......--.---.--- 478 
appendix by...........2..ee2seeees 763 Medicine Bow Range ....-.-.--. 467 
Garnet Cation, Archean exposure in...........-.--- 43 Mount Adams .-- ..--..---------+++--++-- 462 
Garnetiferous schist, Cottonwood Cafion, Wahsatch. 47, 48 Baker. ....--.--------- 462 
Gay lussltee a. see - be see aee ne ee snelan cole sea eoeeene 511, 512 Bonpland .-...-.---- 479 
of Lagunilla, Maracaibo nico coscessoeacs 517 Hood ..-. 462 
thinolite crystals of .............-----.--. 517 Rainier 462 
thinolite pseudomorph after. .-......-.--- 518 Saint Helens ..-.---.---------+---+ 462 
General Atlas cesses serena ccs cesses ee ecanc-ecnccees 4 Shasta 
General geology of Green River group . - 378, 379, 380 (extinct), Quiednanove Peak.........----- 416 
General ice-cap, British Columbia... - Shee 459 Shoshone Peak 463 
General relation of volcanic rocks ........-.--.----. 546, 547 Sierra Nevada og 463 
Genesis of granite and crystalline achists Sousa sceess 112 (extinct), traces of, in Colorado Range... -. bay 
volcanic species...-...-.---. seseeeuesess = die Uinta Range .-----.--------- So COCO ie 
Geode Cafion, Uinta, Palzozoic 145 extinet 470 
Triagt oe eee 262 (extinct), Wahsatch Range.-...--.----.--- 474 
Geognostic position of crystalline schis 118 (extinct), West Humboldt Range ..-....--. 476 
granite ...... Aconobsoccnaccce 118 (extinct) and cafions..................---- 467 


50 K 


786 INDEX. 

Page Page. 
Gneiss, chloritic, Elk Mountain .........-..--..----- 33 | Granite Little Cottonwood Caiion, Wahsatch ....... 45,46 
Clear Creek 26 mechanical hypothesis of -- 118,119 
66 mechanical origin of... -.-scsnacceecssc-cene 120 

. 23 Mount Tenvabo, Cortez Range ..-.--........ 73, 7: 
wees 33 Nache’s Peak, Truckee Range..-....:...-.-- 94 
Farmington Cation, change of position of oldest body of, Colorado Range ......-....-. 24 
MIN Cras Wsasee ee sees na ene eee 50 Oreana, Montezuma Range........-...--..- 89 
hornblendic, Farmington Cafon, Wabsatch.. 51, 52 Pahkeah Peak, Pah-tson Mountains........ 92 
TAR GURRUE Osos ceceacestacatseeemecteee tenet 96, 97 Pah-Snpp Mountains ....... easina\asesecincoe 92, 93 

Medicine Bows22is--.2s2.es-5-sceeeeetesess 30, 31 Park Mountains, Toyabe Range .. 7 
minerals rearranged by compression ........ 66, 67 Peavine Mountain s...--<cssse-eemerceeeeees 97 

Mount Bonpland, Humboldt Range. .-- 65, 66 Ravenswood Peak, Shoshone Range 7 
Mount Zirkel .... 38 red, of Colorado Range. ..:...--....---..-- a 23 
muscovite, Farmington Caton, Wahsatch . -. 5L Shoshone Range ..........-.-..- es 77 
Ogden’s Hole, Wahsatch .-..........--....--. 53 Spaulding’s Pass, Pah-Ute Range .......... 84, 85 
pearllgra vaste see ss sees eae ae eee eee 25 Summit Springs Pass, Havallah Range...-. 80, 81 
precipice, Mount Bonpland, Humboldt Range 67, 68 syenitic, Franklin Buttes .................. 62 
red, Snake River ..-....-- = bHosoartcoms 41 Toan0 Pass) oc sen - or ease -nacsesccseecese 57 
Gneissoid porphyry, Pah-Ute Range. ....--..--.--.-- 84 Toyabe Range -....--.<--------- 15, 76 
Godiva Ridge, Green River group of .........-...--. 385 Trinity Peak, Montezuma Range.. 88 
Golconda, quartzose propylite of.............-...--. type I, muscovite ..-............ 107, 108 
Golconda Pass, basalt of..-...-..-- II, biotite.....-.. CHS OSE DODOSSOCnIS- 108 
III, biotite-hornblende ................ 108, 109 
Good Pass, granite porphyry of .. eee IV, plagioclase-hornblende-titanite. . - 109 
Goose Creek Hills, Archwan of......----.---- OACEEC 55, 56 Wachoe Mountains ..........-....-..-- 59 
granite porphyry of .... ....----- 595, 56 Wah-Weah Mountains 74 
rhyolite of 610 near Winnemucca Lake, Truckee Range. .- 95 
Gorgonio San, Pass, sand of ...-.. 507 Wright's Caton, West Humboldt Range. .. 8 
Gosinte Lak@\c-.-2-.sseseeseces= 446 Wosemite Valley, -.<2<sstenccceeccecesscesee 120 
Geposits Of: 2.cccsessacscs cece sseitens 446 | Granite dike, Summit Springs, Havallah Range .... 81,82 
extinction 0f -ces-cs-ceseaseceesecoes= 447 | Granite. Mountain). 2----<22-22-- ns>-ecccecincenceos 279 
Gosiute: Peake: i... sc.ccncsdies-saacce 203 basaltof So-censcseeceeees 605 
Gosiute Range, Archean granite of... 57 of Pah-Ute Range. ........ 83, 84 
Weber quartzite of. . . 216,277 | Granite Point, basalt of ..............- 668 
Gosiute Valley, andesite, hornblendic, of............. 562 rhyolite of ... 2 634 
Grand Encampment Creek, Archwan rocks of. ...... 39 | Granite porphyry of Clayton’s Peak, Wahsatch.... 46, 47 
Grand Encampment Peak, amphibolite ot........-.. 40 Good thas senstiscsescoseacaaen. 547 
Granite of Adara, Donegal, Ireland................. 60 Goose Creek Hills............. 55, 56 
Antelope Peak, Montezuma Range. - 89, 90 Seetoya Range ..... 73 
aplitic, of Colorado Range. ...... 22,23 | Granite Range, Archwan ..............-- 55 
Augusta Mountains............. é 20 TOCKS)\Ofs--s=.-- <= 93 
Bardmass’ Pass, Havillah Range...-.-....-. 83 | Granite Springs Range, glaciers (extinct) of......-... 76 
remarkably basic, of Wachoe Mountains ... 60 | Granite and crystalline schists, genesis of .......... 112 

bedded, of Long’s Peak. .-.....:....-....2- 26 petrologically com- 

Californinsborder:-2-a.--<ssese 97, 98 pared = 111 
Citadel Peak, Raft River Mountains. 55 | Granite and later sedimentary rocks, relations of. .. 111 
Clarkis:PenkPesnasascasesseasconeeeetecsaee 90)31' || \Granitio porphyry, ss. .eesos=s ee snncewsec sesame =e 61 
Clayton's Peak, Wahsatch ................. 45,46 | Graphite of Colorado Range .......-..-....-..-.---- 27 
ClnrovHalis 2eeaccentreeteea et aan - 72,73 | Grass Cafion, rhyolite of é - 646, 647 
conoidal structure of ..-..... = 11020119) | (Great Basin ecocesecceoteen eee eaeeene ee tenee 525 
Crawley Butte .--..-........ 37 Cambrian and Silurian of......... a 184 
Crusoe Caiion, Pah-tson .....--........t..c6 91 Devonian Ogden quartzite of.........--. 193 
dark red, at Dale Creok.........-...2....--+ 26 lakes, present rise Of. .< <2. 5. cece ccence 525 
72 Ogden quartzite of .....................- 194, 195 
96 Palwxozoic province of ......-..--. 181, 182, 183, 184 
7 present dryness of ... ...........-...... 525 
80 Upper Coal Measures of. ...........-.-.. 221 
Frémont’s Pass, Humboldt Range.......... 63, 64 Weber quartzite of-..--.....-........--- 213 
geognostic position of ......... 118 western boundary of ...............----- 14 
Granite Cation, Cortez Range..-............. 71 | Great chain of middle Nevada, rhyolite of .......... 615 
Granite Range ....... ems ener domeaciset ee ne 93,94 | Great Plains......... BA ROR AACE OCeBAO ICC 020 6 
Grass Caton, Kamma Mountains - 92 Fox Hill Cretaccous.-......-.... 320 
intrasive, Colorado Range . 2 Miotenos <.25.2es2.ce~ 2 co seeseee . 541, 542 
Kinsley District........... Soa 61 vertebrate fossils in........... 411, 412 
ake Ranges. con wascscscacecsaee cee tecce se 96 Niobrara group of: ..... 2.2.2: ccsccnsees 425 


INDEX. 787 
Page. Page. 
Great Plains, Pliocene of ..............-....--- Beccen ADTF 408) | MH aLIerATNOM sn - ceces oceans cnscmccaasaccs==isaae 4, 551, 602, 629 
post-Pliocene disturbance of. .........-- 488) | Hague's Peak, altitude of. --.........------.---:.2-- 6 
Tertiary and Cretaceous age of --....-. 6 centre of drainage...-..--....---.--. 18 
valleys of erosion on .......-.-- Be Gey eballsProf. wiamesssseeeee. sees en ee 187, 206, 207, 210, 280, 294 
White River group of.....--. -. 409,468 | Hallstadt beds..-.....-...------..-..- Baeoronnee toes 274, 347 
Great Salt Lake, rise of. .......-.---.-- 2 505 | Hallville, Laramie Cretaceous . 337-338 
Great Salt)}Lake|Desert ..-.--.-----<----.----2ac--0- 12 Vermilion Creek group of.....-...-..----- 365 
Greenpitiversboainteeneeecessmet ses es a aamenea ee see 8 | Hams’ Hill, Fox Hill Cretaceous .-..- 325 
Green River group of .-- 381 | Hansel Spring Valley 196 
Green River City, Green River group of..-- ac 388 | Hantz Peak, basalt of 654, 657 
Green River group: .-<<--.<s<s<2--c.-<- -- 377, 446 Colorado Cretaceous 314 
Alcove Ridges .......----...-..-- 388 trachytesewes-peen=-seeene eee ae eee 582, 583, 584 
BigiHorniRidges--c-+--------1--2- 387) |eblardin'Citysbasaltiofacces sccee cease seca eee eeeee ae 70, 671 
Bishop Mountain ... 387 | Hastings Pass 204 
Bridger Basin....... 388 | Hat Island, Wahsatch limestone of. . 200 
Brown’s Park....-.. 3840 Hau rhton cited ance a ceseemr ener sa eee eee eee 110 
Cathedral Bluffs occ 382 | Havallah Range, Archean rocks of....--...-.--..-. 80, 8L 
Cherokee Ridge....-....-...----. 383, 384 Bardmass Pass, granite of .... .... 83 
coaliinWeec-s-esoecteerccessees 391, 392, 393 Dasalticcaen<ccce=e accasbisceeséccor 664 
Dead Man’s Springs..-.....--..--- 390 dioritoid granite of.-........--...- 82, 83 
Dixie Valley. ....-........ 392 quartz inclusions, liquid carbonic 
Elk Gap. ----- 385 AG Ws nesnssncossnes Seccceac 81 
Elko Range.... 393 Thyolite Ofc eance. secoeeeaeacaas 636 
fossil fishes of. 394 Summit Springs, granite dike .... 81, 82 
fossillinsecta(ofe.ss-ssesnesee ssc 394 Summit Springs Pass, granite.... 80-87 
general distribution of .... 381 | trachy test. <<. ena=-eceeies neces 6U0 
general geology of. 378, 379, 380 Wh eagetSecheticanscadancoscernss 280, 281 
Godiva Ridge..... eee 386 | Hawaiian Islands, olivine sands .........--..---.--. liz 
Green River Basin. ...........--. Hawes’ Station, palagonite .......--..--------.------ 416 
Green River City ....-..-....-.-. Hay dents Viessa=seseee a= 2, 3, 127, 298, 347, 348, 354, 445, 451 
Green River Valley. x Hazard, Niobrara group of 429 
Huntington Valley ..-...-......- Heber Canon, trachyte of 587 
lithological character of. Peak, trachytes of oo 586 
Monte Bolca, Italy..........-.--. Helderberg (Lower), fossils......--...----.--------- 191 
Nevada, extension of.........-... 38 1p eHelderberg)(Upper)e-s--eseee eases secene sae aes es 206 
nonconformity of, with Bridger fossil S)ssee= === 201 
(ERIN sons bosbaapSssososaSna seas 389 Pinion Range 210 
Ombe Mountains. ................ 391 | Hematites, slaty, Ralston Creek, Colorado Range..-.-. 105 
odlitic limestone of......-...-.--. 382 | Henry Mountains, age of............----.--.----2--- 548 
OquirrhiRangetesn-sc-- so=- ese aee 393 OPAC DYLOS =a eesene saa se eeeeia= ae 548 
Peoquop Range. .-.........-...-.. 391,392 | Henry’s Fork, Bridger group of.......-..-...--..--. 402 
Piedmont)c<2oa-sa-ceacc saecase ose So0ng0 ls erechel’one en. --eeease eee aan ag cttt tec se reece 703, 727 
Quien Hornet Mountain .-.....-.. 390 | High mountain regions, débris of 
relations with Vermilion Creek Hochstetter, F. von 
BLOUP So ens crac oct seccse ese 378 | Holmes Creek, Humboldt group....-....-...-.------ 438 
River\Range:.s2--2ssssce- se eo ecs 392 | Holmes Creek Valley, rhyolite...-.....-.-...------. 610 
Stockton =e. soon ee e S93h fe Hoplans sWallinmsesseseeeeee eesee eee 696, 697, 701, 702, 718 
Sunny Point ...-. sete 385 31 
Tabor Plateau 387 40 
Vermilion Bluffs . . . 384 33 
Vermilion Creek ...............-. 386 562 
Washakie Basin ................. UBL 52 
White River divide.............. ue7 Bobet. ss os ose soe Sees ccteee es 25, 32 
Green River and Laramie groups, nonconformity be- Garnet Canon, Uinta Range..... 43 
Lhe RO ACIRCa SeROC DOD URCOOO A BOLE ASHEAS eSSeaoease 371, 372 Jack’s Creek Cafion . 2 40 
Green River Valley, Colorado Cretaceous .........--. 315 Mount Zirkel......... S 38 
Green River group of... --. 387, 389, 390 | Horse Creek, Niobrara group of ..--...--- 429 
Grinnell i Qo cee ccisesniscsce meets eae ee ne en ses 132, 408, 455 ALTINBSIC OLeae awe no nes ce ncee cwcat ces 252 
Grizzly Buttes, Bridger group of ......-........---. 401 | Hot Springs, Ruby Valley ..............- .--...---- 503 
Gumbel'S.222 22. soricoseesiscesecen accor = 117 | Humboldt, Baron von. .-- 5 
Gunnison oe ens s-== 5 De etm boldt pron sc... se= ss anceee wee 434 
Gunnison’s Island, Wahsatch limestone of .......--. 200 basin of Utah. E 6 434 
Gypsum, Jurassic . ...........-....-... SA CeEREA 286, 287-292 Bone Valley ...--. Sagbos Compo seads 439 
Bey ECO Oi anspcconsesasoncepooconossesccacnas Harlin Cache iValley: cancdtsa-escsscenen es 436 


788 INDEX. 
Page. Page. 
Humboldt group, disturbed near Mendon.......-.-. 436 | Inclusions, fluid, in quartz, Jack's Peak Canon..... 40 
Holmes Creek .---- 438 with salt cubes, in quartz of diori- 
Humboldt Valley.. 438 tic gneiss, Rawlings Butte...... 42 
Huntington Creek 438 with salt cubes, in quartz of gran- 
Morgan Valley........-----.------ 437 ite, Seetoya Range -............. 74 
Ogden Valley -. 436 with saJt cubes, in quartz of gran- 
Peoquop Pass. . 438 ite, Wachoe Mountains. ........ 60 
Pifion region... 439 with salt cubes, in quartz with 
Pliocene of-ce.-sensssssaeeesesae 434 granite porphyry, Seetoya Range 75 
Thousand Spring Valley...-...--. 438 liquid, carbonic acid in quartz, Havallah 
LOanO/Passjcececceweseeacasescace 438 Rang@saseesssesseeceneceaeeae 81 
Wahsatch region ......--.--....-- 435 carbonic acid in quartz, Jack's 
Humboldt Lake, chemistry of. .-.... 510 Peak Cafion..... OS See noSoaconnC 40 
Humboldt Pliocene, Citadel Cliff - 438 carbonic acid, Pah-Ute Range . 84 
Humboldt Range, accessory snftieaail in Archean Indian Cain, Koipato Trias..........-..--.-.--- 272 
rocks'0fs.ss.ccosseseosecs cosas 70 | Indian Pass, basalt of .......-- 667 
albite in granite of.......-.......- 64 | Indian Spring, trachyte of...-. 601 
“Archmean:of-..--=-1s-)022 62 | Infusorial silica. .....-...... - 416, 454 
Archean dolomite of ..........--. 68, 69 Rossili Hill sees een esee eee ees 419, 420 
Archean quartzite with gneissof. 68, 69 Kawsoh Mountains 419 
Clover Caiticn, Archean quartzites Little Truckee River - 419, 421 
DP Seen osagee ancocHacs Sse coe ose 69, 70 Mirage Station 5 419 
Clover Peak gneiss.............-- 66 Reno.....-.... - 419, 420 
Clover Peak, phlogopite in gneiss Sam's Station 419 
Of saceece cues semen eeraeeene naan 66 species of 420, 421 
Devonian, Ogden quartzite of ..--. 193 Warm Spring Valley 419 
elevation of.. .-....-.-.----.----- 12 White Plains Station ............--. 421 
Frémont’s Pass, granite of........ 63,64 | Interglacial era, an ageof dryness...-..-.---- 524 
glaciers (extinct) of ......-..------ 475 Mississippi Basin 459 
Mount Bonpland, gneisses of. ----- 65,66 | Internal evidence of compression in Archwan aay 105, 106 
Quartzitic schistsin............... 65 | Irish granite, spotted schists with ...............-.. 9 
relation of Archzan to later rocks. 62,63 | Iron Point, quartzose propylite of........-.....----. 560 
Wahsatch limestone of ........---- 204 | Isothermal couches, topography of.......... .--.--- 703 
zircon in granite of...........----- 64 
Humboldt: Rivets--c~ sesss- sane -se nse ea renters 13 
basaltiof'.-- he. eee 660 | Jack's Creek Cation, hornblendic schist in. . -...-. 40 
North Fork, alkaline deposit of. . . 502 quartz inclusions, fluid, in..-.. 40 
Humboldt and Niobrara Pliocenes, faunalidentity of 457 quartz inclusions, liquid car- 
Humphreys, General A. A..-....-.---2+--20--200--5 427 bonic acid, in..-.--..-------- 40 
HruntiP: Sterty: he. coos anette seer omnes 114, 116, 117 Jacob’s Promontory, andesite (augitic) of. - . 574,575 
Huntington Valley, Green River group of .....-.--- 392 rhyolite of...--..---- 329 
‘Huronian’s psec tee ee ee 102, 103 | trachyte of .......-----+------ 600 
distribution of seh .-- 102,103 | Jacobsville, rhyolite of -...-..----------------+++++- 627 
sedimentary origin of.. 112 | James Island, Galapagos. - bGo5 = 417 
Hnronian and Laurentian petrographically compared 103,104 | Japan Current......-..-.-..----------- : 4u4 
Hyalite ou basalt)=.s---tessseueeeeseeseaeesee==ee f22 | Java, palagonite of Dyampang-Kulon.. -- 417 
Hydro-mica schist, Garnet Cafion, Uinta Range..... 43 | John Day River, Miocene of .......----------------- 418, 423 
Hypersthene in gabbro........----------+--++++-++ 27 | Jordan River ...-..-------+-+++ sreee----sere sere ee 12 
Hypogeal heat, Sir Humphry Davy’s chemical Jordan Valley, trachytes of . 588, 589 
theory: Of-scecsects-dcececoveccseceteds sesentensees 696 | Junction Peak.......--..- ql 
CD iesooansosapoese3 285 
Ashley Creek ........-.--+--------------+----- 292 
Ice-cap, general absence of, in United States Cordil- Augusta Mountains 294 
leraa).. 2. ssevenccciegoces sce seecseecseeesne 459 Big Thompson Creek + 286, 287 
northern, absence of, discussed .- 463 Black's! Hon kKseece<tortecrece-lsieeeiceesi 291 
Aimenite of Chugwater,.cc-sscssscesscaresseseeeee sae 27 Box Elder Creek. -. + 286, 287 
Inclusions, fluid, in apatite of granite, Wachoe Moun- ~ Buena Vista Cafion -. 273 
tains)cct< ona. ecee ee epee 60 Colorado Ranges sceecienecectsine cn nawewe<-anan mem 285 
incalcite of Archean marble, Kins- Devil's Slide, Weber Cafion 293 
ley, District)222.s2.2-- se ssaee ae 61 Vlaming Gorge -<..... <.---\:<=-<ss-<-- 290 
carbonic acid in quartzes of granite fossils, Como ..... - 289 
porphyry, Kinsley District. .-... 61 Uinta Range .........-.--. 291 
in quartz of granite, Cortez Range. 71, 72 gypsum....-.....---.----.------ 292 
in quartz of granite, Pah-supp TiaranliOsHillessess-ecoceseceesseaaceslacnaesimee 28 
Mountaing)ssscceceastesi-i=-lo< == 93 Mariposa, California. ..-...--.- -.--------+----- 295 


INDEX. 789 
Page Page. 
Jura, Mount Corson ....-..--.---- SECO DES CSa5> 290 | Lake Lahontan............-...--. 13, 490, 495, 504, 506, 507, 524 
North Peak ..- 288 alkaline carbonates of....-.-.---.--- 513 
Obelisk Plateau.....-...--. 292 SGU Ofe es aee eee ese een ne eee 505 
O-wi-yu-kuts Plateau 290 area, aspect Of ---<-----2.----------- 006, O07 
Parley’s Park......-. SER SAS OaSSSCESSCoaaSS oose 293 chemical history of...-....--- 519, 520, 521, 522 
IettyetY oe anascob caDoeOnOeee 292 chemistry, climatic deductions from. 523 
Rawlings Peak fossils 290 Gesiccstioniofiess--er=-aese=e-n--5 ee. 522 
Red Buttes .......-....-.-... 288 productsjof. =~. -.--...--- SIL 
Rocky Mountains .--...-.- Osroce SoS Saas RScHoSS5 285 flood-periods of, correlation of Glacial 
GENO: osoes5ss5 00soRSs apscoce necconcoec es OcoSES periods with 524 
Sheep Creek .. FOSSil5 OSes e eae 2 509 
Uinta Range ..-- height of terraces...---..-----.----- 518 
Wahsatch Range ARGUE tee eres ooe aoe ssoscon- 404 
Western Nevada Lower Quaternary of. ----- - 508, 509 
Jura and Trias, comparison of, Eastern and Western mechanical deposits of . 508, 509 
Prov IN COS hence sea eines sees clean = 343, 344 possible outlet of ....-...---- 2 505 
Jurassic crocodiles . 346 relation to Lake Bonneville. .-.-.-.-. 504 
Dinosaurs - TRVOLS| Ol gee a salen eee an ate atrnee 504 
LOSBLLS eee eee eene oe eee eeencemen nese sees saline efflorescences .....------------ 513 
PC VDSUM eee aceeaa seenereeaaa een eseeanicnan = thinolitelofees=-—-eee-eheee nessa 514 
TOptilesiecaaeeeees sna tufa of 514 
Caiion City Lake Lahontan and Lake Bonneville compared. ..--- 507, 508 
Morrison ..-.-.. ake; Marian; glaciers /0fcc---< pececnacenerieeen ev amar 476 
slates, microlites in -........-...---...-.-- 295 | Lake Range, Archwan mountains...--....--..------ 96 
Pana pees oss seccesas ceeceseecas cae 96, 97 
granite ..- 96 
Kawmma Mountains, basalt of.......-...-...--------- 668, 669 thinolite of. . 515 
Grass Cafion, granite ..--------. 92 trachytes of. 601 
hornblendic andesite of......-.. 564,565 | Lakes, Bonneville .........-. 12, 436, 437, 466, 490, 492, 495, 496, 
rhyolite of-.------.-...-- senses 648 498, 499, 507, 508 
trachytelOfcen-sre-aess so sste- a 601 Carnicde-cceaciconereseeseeerceaseescem eaten 622, 623 
Kamas Prairie, Palzozoic of ......... ---.------.--- 146, 147 441 
trachytes of -. 586 455, 456 
Trias 264 Compass sceaseeeee eae Cen OSGHOdaSOEES 289, 310, 312 
Karnak, rhyolite of 644 Magle sraceciseeela seme sain meee ee ae 660 
Kawsoh Mountains, basalt of ...... ....-....---.---- 674 rani eee asec see eae 475 
REACH Yt Olisessmceseese sess == see 601 Gosiuteessesseeee = ene ecee ac eoe = -- 446, 447 
Truckee group, Miocene of ..--. 415 Humboldt 510 
LIGA E ssscooseseeo cass Bentigg -eescOnccOoSSBeRHSenie 716 Lahontan ....13, 490, 504, 505, 508, 509, 511, 513, 514, 518, 
Kinsley District, Archzan dolomites of Seas 61 219, 520, 521, 522, 594 
marbleol---o- eee Gil |) AMIN coh cohen ccorencesccaass cceeisssssacece 476 
fluid inclusions -- 512, 513, 525 
in calcite of. -- 6L 
rocks of ~ GOR) EARS eR cesses ceo she saose bees sSSsaSs 
PTQNILG Ofeeseee seen aeeee eee ee 
quartz of granite porphyry of, in- 
clusions, fluid and carbonic acid, 
see sene Setconnd SSSpanascHNCOHaCS 61 -- 
Koipato group, Buena Vista Cafion, Trias. ..-........ 273 Soda ...--...-...-.--0enc---000- cesaen 510, 512, 513, 514 
Triagnesecceccscsecesee es 269, 270, 276, 279, 349 Winta tecasscs sos occ wees Se ws ec ooeees 444, 449 
Why coe o9s ssaasseroncdassoosa cascosdeaSesces 445, 446 
VA SG) 5s ceeoaacenns cen coscos cosacean 447, 448 
eapradorites--.<s=-- sense eeeenae= aeeeneecessse=-a== a 27 Winnemucca .--.. -- 95, 505, 519, 650 
Lacustrine Quaternary...-.-..-- 494 | Lakes of Glacial Period .....................-..---- 438 
Lagunilla, Maracaibo, gaylussite of 517 | Lakeside Mountains, Wahsatch limestone of.....--- 200 
Take BONNE VIG sonsecie ces s-ieseeecinaeeesetia= seen TEACGUAZIND |) JEONG a penn sinresecorenncososcsc ee Teo e cesses 1 
chemistry ofies--s-eeeseeeeeeseseeee 498 | La Porte, Colorado Cretaceous .--..---.-----.------- 308 
evaporation-products of..... 488, 494, 495,499 | Laramie group...-..-..-.--..----- 343 
mechanical deposits of ........----- 492 Cretaceous . 331, 350 
OUtlOt Ofeeseemen se eee ene are 492 of the Great Plains .....-.-.. 331, 332, 333 
terraces Of). ---—- ===> = SCer oOo EEeaS 12 relations with Vermilion Creek group -.--- 375 
tufaiofe ans anpaeeceaeneceeseeanere 495,496) |) Laramie Hills. --- 2. <i. ee seen mene cman enecn ene -n-= 17 
Lake Bonneville and Lake Lahontan, comparison of- 507, 508 Colorado Cretaceous .....--.--.------ 306, 307 
their relative Dakota Cretaceous.......-.--.---- 299, 306, 307 
positions. ... 504 Qo 6655066 2505 20S bs DOSES OS EOEEO 288 


790 


INDEX. 


position and altitude of............. 
Masson's Peake -. vo. scsac2ss encee=seseeceeosestees 


Last Chance Spring, andesite (augitic) of 
Poaurentianyacccscec-sscaes see ee cee noeteeereee eee 


Call yen ee ewer ene esssceenemelieaeeciac cs smaaaneee= 
Leach Spring, rhyolite of .... 
Le Conte, Prof. J. L........-.. 
Lepidolite 


in granite in Crusoe Cafon, Pah-tson 
Mountains \scen<mses-= eeiseenuclsnemescere 
Lepidomelane....-...--.--------. 
Lime Pass, Palzozoic....-.-.... 
Limestone, Miocene. ..... 


Lithological caaracter of Green River group ......-. 
Little Cedar Mountains, Coal Measures (Upper) of-. 
Little Cottonwood Canon, glacier (extinct) in--...-. 
Little Muddy River, Vermilion Creek group of ...-. 
Little Truckee River, infusorial silica of............ 
Lodge Pole Creek, Niobrara group of .-......--..--. 
Logan Caiion, Waverly group of .-........-...-..--. 
Lone Hill Valley, Miocene Truckee group in ....... 
Lone Tree Creek, Laramie Cretaceous .............. 
Long’s' Peak, granite beds--..-~...-..0<secessseeceee 
Lovelock!s Knob, basaltiofesascaescsccecsceconeseees 

rhyolite|Offescass=ac= ton ceecert tee 
Lovelock's Station, basalt of ..... 
Lower Cambrian slates. - . 


25, 26 


147, 149 


416 


175, 176 


496 


380, 321 


223 
474 
363 


429 


Lower Coal Measures, fossils in, but not in Upper .. 244, 245 


Lower Quaternary fossils.............---.------..-- 494 
Lower Quaternary of Lake Lahontan...........--.. 508, 509 
Lowest descent of (extinct) glaciers................. 476 
Lyell 'SiriCharles: 2-1. -ecccccdveseenascsteeetaseeee 706, 716 
Madelin ‘Mesa; basalt of.cc.....cosccessasccesesee- tes 671, 672 
Magpie Peak Thy0lite Of secesastmaces cesses cece eas 619 
Maggs’ Station, saline efflorescences of..........-.-- 513 
Mahogany Peak <2... ssicec-ccrscceniseaes oa tat eeeeceee 203 
rhyolite of 613 

Malade Valley 2222.0--=ssee recess 195 
Malheur River, Miocene of 413 
Mallard Hi.ls, rhyolites of 615, 616 
Mallett, Robert 697, 698, 699, 701 
698, 699, 700, 701 

Manitoun)..coasccesosjaenamctese senate 101 
Map I., area of...... 5 5 
Mapl ih: ;ates Of; ...c-.cctiessneeve nase one cee t eee 8 
Map Ill Sareaof). ficbeae sec tee ott ce eee eee ee 11 
Map IV., area of .- 12 
Map V., area of. .... 13 
Mariposa, California, Jura of 295 
Marah sO: CO. -.gcneccneran 285, 423, 439, 443, 445, 449, 450, 454, 591 
Marvine, ArchibaldiRi.scscceeeseeeeeenea teen eee 23, 649 
Material of Glacial Period transported............-- 483 
Matlin; ‘basal t,ofi:52-.5.sec ss ace rented cent eeseee ee 658 
Mechanical deposits of Lake Bonueville 5 492 
Make*Lahontanie...ccseeeese 508, 509 

Medicine Bow Range, Archwan of...............--- 19 
Colorado Cretaceous .......... 310 


- 
Page 
Medicine Bow Range described ...............- cade 19 
geology of......... - - 28, 29, 30 
glaciers (extinct) of . 467 
PMEISKOR Of jas nee nse saene ens en SONS! 
Minerals of Archzan rocks of. 36 
PRalwozoiciof.2-----<=-se-6==6 135 
IL TiasSIG soso coe 250 
zircon in granite of. . 31 
Medicine Bow Station, Colorado Cretaceous. . = 313 
Fox Hill Cretaceous. ......-- 322 
Medicine Peak <q .cc<ecesectee ss -senncoseaan ABSDOORaCe 19 
altitude of . 7 
quartzites of 34 
structure of. : 34 
Medway trachytes 2 --2-c se -osaccccsectcaseshiesaceses 588 
Meek? Prof. Ba B=-ccces <<a eeeerace eee penne a 211, 328, 423 
Cretaceous section by... 4 297 
Meek and Haydon): <2se5-sceae eee eee enone cone 331 
Meek, Hayden, and Lesquereux, conclusions on, 
Laramie Cretaceous: -.-..-2----2sse-6 === cect es sas 351 
Melrose Mountain, andesite (augitic) of ....-....-.-. 572 
Mendon, Humboldt disturbed near.....-. 436 
IMGR0Z016 aces enaedaieeneecie 2 249 
province, Nevada.. . 346, 347 
recapitulation) Of -s-seceseeean eee eee eee 340 
shore, Wahsatch region .........--.----.--- 341 
western Nevada province....... 341 
Mesozoic and Palzozoic, relation of ...... 342 
Metamorphic granites of Colorado Rango 101 
rocks, Archzan, their difference from 
Oruptive!s--3c--ene=-2esea- eee 100, 101 
Metamorphic and eruptive series of Archean rocks. 99, 100 
Metamorphism, Archean, pressure always accom- 
Panied DY) -s-sasca-sewicesee=/o5 ses 113 
in depth, Archwan section, incre- 
ment Of---<-sco-2-eo-eaesc-aseeee 106, 107 
Microlites in Jurassic slates ..........-.- 295 
Middle Nevada, alkaline incrustations of. -- 502 
geological relations of --- 615 
BANOS Ofvecena ecccaciee tenn nee 502 
Middle iPass icceacccc sna eeon ete eo cence eee 276 
Mill Peak, altitude of ...............--... 35 
Archwan conglomerates of. . 35 
limestone of......- 35 
quartzites|Of--~-c-sacnten= enna 35 
Btructure Ot. .oeesren semester 35 
Mineral Hill ...... cease OsSoS SEGRRRSHANS ESE 191 
Minerals of Medicine Bow, Archzan rocks . 36 
Miocene, absence of, over Utah..-.-.-----.-- 412 
aj OnePass (ccemciec=acmctise noses eem=eteees 413 
Chalk Bluffs...-...--- so concoonesossatoce 451 
Crooked River --. - 418, 423 
Des Chutes River ..-..- 5 423 
distribution, Sioux Lake . 451 
Wossil Hill 222s ct3o- eee centers Se sie s ae 422 
fossil’ mollusks \enee = ws encase aeesieseeee 422 
GreatiPlains @-s-o.ess- see ene . 541, 542 
vertebrate fossils of - . - 411, 412 
John Day River:2.-!--.cssseccn~ =e . 413, 423 
limestone pencnaeresneecennesccencconcere cme 416 
Malheur River 413 
Oregon -canccecea== 423 
Pah-Ute Lake..... 454 
Sioux Lake...-. 451 
Tertiary acaceaecsessens 408 


INDEX. 791 

. Page. Page 
Miocene, trachytic tuffs.....----.---.------ eae 418, 422, 423 | Mountainedisintegration, of peaks ..-....--.----.--. 472 
Truckee..-..... ase - 454 Rocky Mountains.--..--- 472 
Truckee group ...-.. ...<<.------------0--» 412 Sierra Nevada .--. 72 
Boone Creek .....-----.---- 414 Uinta ....-.. 472 
Buffalo Peak region ---.-.-- 414 Wabsatch . - 472 
Kawsoh Mountains. - 415 | Mountain topography, Quaternary.-.---.------.---- 528 
Lone Hill Valley -- 414 | Mountains, Adams ...-........----------------------- 462 
Silver Creek 414 Agassiz -. 152, 153 
Valley Wells ...-.- Sas ccaersor a sonce 422 JAR poeaansses 627, 629, 630 
vertebrates of Oregon .. 424 Aqui....-- : ae 593 
Walker River -.-.---.-- 413 Archexan...-...--- adastogasssceesraeacs 96 
Western Province. ...-- Baio 542 PAU PUBLA acme e= l= 79, 80, 281, 294, 575, 631, 663 
White Plains Station........-.-.-- ecccsecs 422 Pe Venscconososscasc SoS ss9 220, 221, 225, 635, 636 
VID TIS Ge see SES See see SSO SOS .-- 353, 451 Bishop’s 368, 387 
Mirage Station, basalt of .....-..---------------++-- 675 Black Rock . 648, 649, 669, 670 
palagonite of. .....-..--.-.-......-- 416 TB pHeasactoosE cecdesceoseacausopas Osan 452 
infusorial silica of - -- ease 419 Bon DP land eee sees n sane stee eee ae 65, 66 

Mississippi Basin, interglacial era of. ..----..--..--- 459 TSG) < ooeaeceenceeccine cecoodoorssaooesn56 41 
Modern disintegration, Uinta peaks.........----.--- 471 Cedar mtcnes so cecce sass sm onneaemeases 562, 571, 594 
increase of avalanches ......-.---- pSSAOceeS 526 Corson...- ---- 261, 290 
oscillations, climatic evidence of. ..-.--..---- 527 Desatoya .-- 282, 630, 631 
Moisture of cordilleras, sources of...---------------- 525 Diam on dese sae ec aea esate ens 367 
thelGlacialiage cess ens = = waien sea ea 524, 525 TOE Nieteee do oe ee eC E UE BER O SHES tOceoeace 203 
Moleen Canon, Coal Measures, (Upper) .---.-------- 224 DD ee ea oaseceesspeccueconeeoes 19, 33, 258, 302, 313 
Weber quartzite of ......--.---.----- 218 kph ead eeeeee tea a cecetasieeene seen 654, 657 
Moleen Peak, Coal Measures (Upper) .-----.-------- 224 Etna ..-.. aS Seoeee ge caace, 417 
Weber quartzite of .....-...-.-------- 218 Fish Creek - -80, 281, 632, 635, 649, 664 
Mollusks (fresh-water) of Bridger group ---.---.----- 402 TG eo ee eeessono cones ose Soo0 649 
fossil, in| Miocene: < +------==-o=0-in==ere= 4 422 Goose Creek 610 
TT) ERG) senses aac cseec cose Ses CecSeE tee SesDSeHeo 512, 513 Granite .......- . 279, 665 
PRIA Dm andpaccodbecmacnesenaoceOuO CEOHEE 525 Havallah 664 
Monte /Bolea, Italy) ------ ------<.52= on==-- «--- 389 Henry -- 548 
Montello Station, Upper Coal Measures near . 222 TY s-oeeecesectonsecoen. co =cescsesoae 462 
Montezuma Range, Antelope Peak, granite of. 89, 90 Liye sean sacoonnes4 92, 564, 565, 601, 648, 668, 669 
Archean rocks of .......--.----- 87 415, 419, 601, 674 
schists/of ------------- 89 200 
basalt Of --- 22 ooo... ncencen-=ee 667 151 
Kaspar’s Pass, propylite of. .-... 553 Little Cedar... 223 
near Oreana, granite of .... Melrose..-..- 572 
rhyolite of ...-...-.----- IMORES == sees seeen anes seen einai -632, 633, 634 
Trinity Peak, granite of--- ce IN ue soormeso aco lcH CERO nenS --- 219, 625 
Mopung Hills, basalt of.......-----.-----------+----- Ombeess=--— 5; -391, 658, 659 
phy Oli tevatse seen acne nisin =e OQquirthiwsscenatnctccenewesen=-- orn —n 197 
Moraines (terminal), North Park -.-.--.----- 5 467 (Pab-SUpP lessees ee see eee seo aaa === 92,93 
of recession ...---.--- SaeecRaoe 461 Pah-ts0ll-o2---cceeeesoe~~----=--90, 91, 92, 600, 640 
(terminal), Rocky Mountains .- Ietat Opececoaseecoosense ceceaseamnacene 97 
Morgan Valley, Humboldt group of Quaking Asp -- 324 
Morrison, Jurassic reptiles .----.-----.-------------- Quien Hornet .- 390 
Mount Adams, glaciers of ..---.--------- Raft River... 54, 55 
Airy, rhyolite of ...........---.-. Rainier’... csce=2. es =see--=elena=ncensece= 462 
Baker, glaciers of....-..-.------- Richthotensss= ss eses ane eleew eae a= 18, 607 
Corson, Bridger group of ....-.------------- ROCKY saci seen = seen seae eee aee aw ensee =n 5, 21, 124, 
Surneesct eee ee eee enone 127, 249, 472, 473, 579, 585, 625, 653, 654, 729 
Hood, glaciers of ..-.-.--...--- Tae icesceecancennsonce cep ste Rea aRSSSasHC 625 
Lena, Paleozoic of...---------- (Cg Groene reeHcatecssScobccepOSOEone 96 
Moses, rhyolite of. - SteHelousiecascenesc-sseases- eee aeassna= 462 
Neva, rhyolite of .- Schell Creek!-----. ---<..--0~ :. 186 
Rainier, glaciers of ...... .---------+-- ReAsSSo 462 Shasta lccsesie--aansccescce -- 462, 463 
Richthofen, rhyolite of 607 SilVelieesenateea-see see ves 554 
Rose, rhyolite of .......2..-222s-----cece-neee 625 DRUGS ane ann enone ocelot 58, 660 

St. Helens, glaciers of ....-..-.---.----------- 462 Mahlonesnccneseeseaaaaeea— aeons aencon 639, 664 
Shasta, glaciers of ......--..--0-0.-.-0---00- 462, 463 Tenabo 73, 74 
Welths, basalt of 654, 656, 657 Tucubits 610 
Vermilion Creek group of .....- soca 361 Wachoe ... 58, 60, 202, 203, 571, 572, 611, 612, 613 
Zirkel, of altitude..........-.----e-s---eeeee A 7 Wiahwealissesscahee-nasecneessaessence 74, 599, 622 


792 INDEX. 
Page. Page. 
Mountains, War Eagle....--. CERstopacdcto Senonesqoos 105 | North Park group, North Platte... ..............-- 433 
IWiaSnOCS cosine reecine cle ne smieas siecinaiersren » 550 Pliocene of........--- 431 
Wrelthal. <<. <<. 2. cn. cccccecacecass 361, 646, 654, 657 Savory Plateau ...... 434 
White Pine .......- 205, 206 | North Platte River ...........-------------ssecee-s 7 
Zirkliets=ccoccees~= 7 North Park group of......-..--. 433 
Mnd Lake Desert, basalt of 669 
Muir, John, his glacial blunders 477 
Mullen's Gap, dacite of ........-....-220-----eeeeee 569 | Obelisk Plateau, Jura . .. 292 
rhyolite of<see- aesesesesssvnecserese 650, 651 Trias ..-....- 263 
Muscovite in Archwan quartzite ..............------ 69 | Octahedral crystals of thinolite 517 
Felsitic porphyries...-..-.....----.--- gg | Ogden Cafion section, Cambrian quartzite of ........ 175 
Granite, Ravenswood Peak..........-. 78 Ogden Devonian Quartzite. -.. 176 
West Humboldt Range ...... 86 Paleozoic of .......-... - 174,175 
slates, French Creek .........--...------- 34,35 Wahsatch limestone of. - 176,177 
‘Ogden quartzite. <.c-02226-ce-2-- esse ccc aae=s 156 
Bonider\Creeki neces -ess- seen aciear 194 
Wacho'a'Paas..-. <5. -42.-sus-cesesnceceeseenes Hazes 94 Great Basin ..- 194, 195 
NachelsiPenkeeese ee eeeeeenee 94 recapitulation . - - 234, 235 
Nannie’s Peak, rhyolites of 617 White Pine .....- 194 
Natural succession of volcanic rocks...........----- 690 | Ogden Valley, Humboldt group of ...-....----..---. 436 
Nature of Archean metamorphism .........--... 112, 114,115 | Ombe Mountains, Archwan granite of.....-..-.--.- + 56,57 
and solution of Pyramid and Winnemucca basalt of....--.-.-.-2---- 658, 659 
lakes: o...280e. essere eerste here 519 Green River group of. ..... 391 
Naumann +25. .ccosicssseeeee-coese poe ee 117 rhyolite of .......--.------- - 603, 609 
Navesink Hills, Vermilion Creek group of........--. 361 Weber quartzite of..--.--.----.--- 215 
Navesink Peak, basalt of .........-..-..-- . 654,655 | Odlitic limestone of Green River group ....-.-----. 382 
Nepheline of basalt 6567 |/p Ophir Canon eos csen ane ante cee=eeaa= OooreSceac 198 
Nevada Basine css soe een 43 | Oquirrh Range, Cambrian and Silurian of..-.. - 184,185 
Elko; Hovene\:..--c-2----2--cesseess cee eae mmr 450) Coal Measures (Upper) of. -.. 221 
extension of Green River group..-.......--. 381 Green River group of ..... cid 393 
Mesozoic province....-......-- sseuse 346, 347 trachyte of .........---2-.-..-. 4 590 
Ragtown, carbonate lakes of............--.. 510 Weber quartzite of .....-.---..----- 213 
talus\slopesiof-.-~..0s-=s}cccssterjecsees ARGAG 485, |’ Oregon, Miocenelof: .-..----<-- -2cceeceewne-ses---=~s 423 
Névé erosion, peak topography the result of ........ 479, 480 vertebrates of ..........-.------.-- 424 
Newherry,J.S-2-.ce-c-cecccccacecccncscen eeneee 331, 353, 456 pre-Miocene geology of.-- -- 451, 452, 453, 454 
New Pass, rbyolite of 631 Upper Coal Measures of. ........-......---- 223 
Minesi Trias tecse-ssscceanssccnects seceee 262,983) | Oreana; basalt Of <2. --scecnsecceneesemcrccaereamecses 666 
Niobrara group): -<--<--s<\s0scnsanse=soe este eee =, 305: || OrfordtPéak 22-22 scccc cence eee a eaeeeeeeeeaeeeee Q17 
chalk blufis;-s.-ccscene=-keeesceses 426 | Original dryness of glacial lake basins 429 
Cheyenne)- << onc eccra-csesscesecices 5 429 | Origin of Huronian sedimentary. - 112 
Chugwater cceceese <= ssecsces sees 429 | Ormsby Peak, trachyte of....-... 603 
Cretaceous fossils ............-...-- 349)1|. Oropraphical\periods!<----n-ke-===/ceeeeieeeeeeeee eee 758 
Crow Creek:..--. << .cccccssssccssees 429 action, post-glacial .................-.. 492 
geological distribution ............. 4257) Oropraphy.~cacucas-peatereeeeacieces=ttar ee eeseeeaee 727 
Great Plains 425 | _ AT Ch@allseceeeeeca=seeenscnessceeseecesss 729 
PEE OHOCCCOBD EO 429 post-Carboniferons . 731 
429 post-Cretaceous - ... 746 
428 post-Eocene ....-. 541 
429 POSt-d ULASKCeeem ee ectene\seecieo Wesco eee aes 732 
429 post-Palwozoic.......... fe atelwafelele'atelcterastotas 536, 537 
425 post-Pliocene .... - 542 
Post-pliocene tilting of .........-... 427 Tertiary) conc. ..5 = 754 
Utah Basin 2? 435 | Orthoclase twinned in granite. 26 
of the Great Plains, slope of........ 426, 427 | Osino Caiion, rhyolite of..............--2.--2202--00- 617, 618 
Nonconformity between Laramie and Green River Weber quartzite of...............-.--- 218 
Pais Windogeckocsesossece 371,372 | Otter Gap, Vermilion Creek group of ....-...---.--- 366 
Laramie and Vermilion Otto, Niobrara group of .............--2.0.2.2..222-s 429 
Creek groups........... 355 | Outlet of Lake Bonneville .............--..-2220--0- 492 
North Park ic cncocc.ccssees cee casse he eterno 7, \Owen'siloake; rise Of... scene coerce eee aces 525 
basalt (of ’.< 2 o/s 2scc.cecseseoeoneceee 653 | O-wi-yu-knts Plateau, Jura ........--.-....-...-0--- 290 
Colorado Cretaceons. .... - 310, 311, 312 (Palesoz0ig=2- => ose se a= 141 
Dakota Cretaceons .... ---. 301,302 | O-wi-yu-kuts Plateau, Weber quartzite of .....-.... 148, 149 
QI Rees Brccraeaeacnces 288: | Owl Butte;rhyolitelof <<... 2.22.2. -cese-=osseennce 608 
moraine (terminal) of ..............---- 467 | Owl Creek, White River group of . Sciscceo 410 
North: Parkigroup Oljcssncseces cesses 433 | Owl Valley, Coal Measures (Upper) ........ --...-.- 222 


INDEX. 793 
Page. Pago. 
Owyhee Bluffs, rhyolite of.--.-------------- BocOSeLDa 624 | Palagonite, Etna. .-.-.---------- See eeeeecce sae = =so60 417 
Oyster Ridge, Fox Hill Cretaceous --------- 50 325 Hawes’s Station 416 
Vermilion Creek group of ..---------- 372 Mirage Station 416 
referred to angite-andesite..-----.-- 419 
Thingvellir Lake 417 
Pah-keah Peak, rhyolite of-----------------+------>" 645 Ih Panonenue sd aenee oS 5 671 
Puh-supp Mountains, Archean rocks of. 92 Warm Spring Valley .------------++---- 416 
gravite of......-.--------++--- 92,93 | Palisade Cafion, andesite (augitic) Oh pees nase anne == 574 
quartz of granite, fluid incla- hornblendic andesite of 563 
sions in ...------------------ 93 trachyte of .-.--.------------- 588 
Pah-tson Mountains, Archwan rocks in .-.---.------ 90 | Papoose Peak, dacite of. .---------------- 567 
schists 91 quartzose propylite of 558, 559 
Crusoe Cafion granite 92 | Paragonite schist, Garnet Cafion, Uinta Range...--. 43 
lepidolite in Park Range . 57,20 
granite....---- 91 Archean geology of .---------------»--- 36, 37 
tourmaline in Archean recks, minerals in ...--------- 41 
granite....---- 91 Archean structure of .----------------- 37 
Pah-keah Peak, granite near... 92 Dakota Cretaceous ..------------+------ 303 
rhyolite of..----. 645 geology Of. ..----.-+---+2eeeeeseee root 20, 21 
trachyte of. - 600 SYONItC ...-.--0----eee eee ee eee eee 40 
Pah-Ute Lake.-.------------------ 454 'DIG8scpeessincesceses ese ==e-- === 259 
deposits of.-..-..-------+ s++-++- ==> 454,455 | Park’s Ranch, Colorado Cretaccous. .----- ---- 308 
disturbance of beds. .-.---------- asseos 456 | Park Station, Laramie Cretaceous. - - - 332, 334, 335 
Miocene of... ------ 454 | Parkview Peak, trachytes of....-..----------------- 580 
Pah-Uto Range, Archean rocks of. 83 | Parley’s Cafion, Dakota Cretaceous -.- 304 
basalt of _.. 664,665 | Parley's Park, Colorado Cretaceous. ..-.-- > 319 
gneissoid porphyry of .------------- 84 Jura Of .....-.-------~---2 = 293 
Granite Mountain of ...--- eee soce 83, 84 trachyte of ..------ .- 586, 587 
rhyolite ...---------------- . 637,638 | Passage Creek, rhyolite of ....-------------++--++-* 610 
Spaulding’s Pass granite -- 84,85 | Passes, Agate ....-.---------------ce cere etre 219, 661 
trachytes of ...---------- S506 600 PAtatOle soneccccumencesecenseee see caaelea =e 602 
Trias . 278 Wrémontwecessceccsececeoeeeren==1s=2= 63, 64, 193, 203 
Palseozoic.....-.-------- 127 Golconds .-.-----.-.--.- . -280, 560, 561, 664 
Chimney Station 21 Good. ..---00--ce-2-cc0-ccheccocecescceccecen= 547 
Clayton’s Peak..--------------+-- 173 Hastings. .------ 204 
Colorado Range , 133, 134 Indian ....-..- 667 
Cottonwood section .--..------------------ 165 147 
Du Chesne.....--------- +220 rere erent 146 94 
Escalante Hills 144 631 
@XPOSUTES .--------- 22 eee e ee eee etn 127 215 
Gilbert’s Meadows. 150 Peoquop ---.------------- 438 
limestone ---.------ 535 Pine Mountain. 620 
Medicine Bow Range 135 Pifion . .. 
Ogden Canon section . 174,175 Sacred ...- 
Ogden Peok...--------+--+-+--+++7+- 174 San Gorgonio 
O-wi-yu-kuts Plateau. .-..----- 141 Shoshone. ...-..-------- 
province of Great Basin ..--.--- -181, 182, 183, 184 Sommers’ 
province ef Rocky Mountains...-----.---- 127 Spaulding's .....----. 
Rawlings Peak ..---. ------++-+------+---- 136, 137 Spring Valley 
recapitulation Se eC BROS COLLLL Dereon 227, 228, 229 MonnO toot coleesesseesaeeeeaa-—=ac= 
section ....-----------+ sees eee enerterreen? 129, 130 Yampa .....--------ee---es-ee20 > 
generalized...--+..-.----+---+++-+- 246,247 | Peak forms due to snow-erosion 480 
recapitulated.....-----------+----- 164,165 | Peaks, Albion .....-.---- 224 
Weber Caiion ..-..-------- eee ote 156, 157 Moh eeteeoetesceceaee ss cee=ss === =e cenn soe 645 
White Pine .......-.-------------- 208, 209 Anita...-- 655 
series, general geology of...-------- 534, 535 Antelope . 667 
generalized ...-. ------------ 5 536 Amntlor tote o ccnese sece caso ceecnec--ceseesees 219, 225 
subdivisions, tabular statement - - 5 248 Manaltnecocceeccusisceceectincccs=-s=— stuns 669 
Tim-pan-o-gos Peak ......-..--+++++-++---- 172, 197 Black: Butte -....-cssccccccccencscrescoeccen= 336, 337 
Uinta Range..----.------------ 139, 140, 141, 153, 154 Bonneville. .......-.--+ eee ee connect eeeeeeee: 185, 593 
Wabhbsatch foot-hills .......-------+-------+ 173 Box Elder - 18L 
Yampa Cafion......----------++++-- 144 Bruin......--.------- = 38 
Palagonite .--------------++----++2-° -. 416, 454 Buitalo!c-----sccess=-0 268, 654, 665 
age of .....--.---------- ~--. 418, 419 Carlin .....-. .cececeeee cnen eee ere neceeeesn es 563, 621 
analysis of ..-.--------+-++--+-2-+-20e0e0" 417 Chataya - -600, 640, 664 
dependence of basalt ..-..--------++-++++ 419 OlarkBses sucess cecccceccecucesccocsedsoes ity 10,00, 9L 


794 INDEX. 
Page. Page. 
PoakssClayionsi--scecccassccccrcccresceesss 45, 46, 47, 126, 173 | Peko Peak, rhyolite of ........ Btncaéasscceccoce arecos 617 
Cloventesssscascsonescescsacccceenmecicee eee 66,475 | Pelican ‘Hills, Palw@ozoic--.2--.-.....<-.-.-.-.-----+- 197 
‘Gonnorlsisa-c os ssc aee concns cen ceecse ene anes 214) 221" Penn Canopeccessteesscetes ccceceeeeecer eee 217 
Cortez 621, 622 | Peoquop Creek, trachyte of .....- mons 595 
Orescentinessscon--ceeeees 564, 575, 576, 581, 582, 583, 584 | Peoquop Pass, Humboldt group of -................. 438 
Diamond 367 |) Reoquop Range,Arch@an--...-2--2---=--5) ceeseeoee 58 
Emmons’ . Coal Measures (Upper) of .......--. 222 
Rtheliee. ss. Green River group of .............. 391, 392 
Fairview Spruce Mountain, Archean schistsin 58 
Fortification zircon in musco- 
Gilbert's 151 vite schist...... 58 
Gosiute 203 Wahsatch limestone of..-........-. 200 
Grand Encampment... 40 | Peoria, Dakota Cretaceous ....-....-....---..------- 303 
Hague's 6,18 Chr Mek etsces seresnscos 292 
Hantz .......-.22.02---.000---314, 582, 583, 584, 654, 657 Trias. c= 264 
586 | Periods, orograpbical . 
40) Permian). << sc02-----eseeeesseaeeeracee 
141 | Permian and Coal Measures, relations of ............ 343 
562 | Permo-Carboniferous .--.........20cccce--cecceeneee 144 
26 Cottonwood section 171 
95 fossils): 5 s<<<<.shen6 245, 246 
619 LOST epee Somee acess 146 
Mahogany. . 203, 613 Wahsatch:-<2--.0c-<.ssessass 155 
Medicine ... - 7,19, 34 foot-hills=.-<.-+----= 173 
35 Weber Cafion section..-......- 163, 164 
Santee de Anococctiesaoookcoo Sas sdest As P18) 2245] Plath: ee en sac ccan sgn nae ceceenee nee coe ee eee 698 
5 94 | Phlogopite in gneiss, Clover Peak, Humboldt Range. 66 
- 617 granite of Wachoe Mountains ........ 60 
=96); 654,655) Bickeringite)-ce-sse--seos=sseeeeeeeseeseeee =s 499 
Sash aansaache ss ssemamelse seem e see nee 288 | Piedmont, Green River gronp of ....- -- 390, 391 
174 | Pilot Butte, trachytes of ...........-- - 585, 586 
21:7::223) | ePilotePeak-s-..---+s+--=<= ACESS cH One Case Stee OS 215, 221 
603 débbrisjofi tes eee eetocsceccctsc 481 
92,645 | Pine Bluffs, Vermilion Creek group of .-.. - 303 
‘Papoose: =---e-ce-secenseses 558, 559, 567 | Pine Mountain Canon, trachyte of ..---.. A 600 
Parkview 580 | Pine Mountain Ceal Measures (Upper) . - ; 222 
POKO#2 ces sewnessccceeceteeeesesee Soosondess 617 | Pine Mountain Pass, rhyolite of .....-.............. 620 
Pilotic22---csecsenseaseass= steam ateeees 215,221 ,4815)\ Pinto -Peak: cc. sence gece cccensas sacs cess aneanceane 190 
(PintO:s =o -eeescaee So -- 190, 660 basalt of .. 660 
Quiednanove........ a3 = 476 | Pinon Pass, basalt of. - 660 
Rabbit: Kars--cscoccacscccececisacnees ae 633 rhyolite of .. . 619, 620 
Railroad!s2n-socccescenasacieees smemaenaneee 622, 622, 624 | Pinon Range...... COHCE CRSA ABSaactedeosteoss denice 619, 620 
Raven's: Nests. .cs\sssscaseancicates SOCCEECES 189 Cambrian and Silurian of...-......... 189, 190 
Ravenswood : soon 18509 Devonian, Ogden quartzite of........ - 193, 194 
Rawlings... 136, 137, 289 Humboldt group in........-.--.....-. 439 
Signali;cicc sssasestseccnnceleseosecscecee sicees 280 rhyolite of 620 
Shoshone 476, 568, 569 LACH Y tO Ole ceemcs enemas cen ececinees= 596 
Spanish 651 Upper Helderberg .......-......... son 210 
Star .--.- 270 Wabhsatch limestone in.........-..... 209,210 
State Line 650 | Plagioclase-hornblende-titanite granite, type IV .... 109 
Tebog 640 | Plateau of central Nevada ........-.-.--.----.. c 12 
Tim-pan-o-gos 172,197 | Platteville, Laramie Cretaceous 332 
Toano 222 | Pliocene lakes and their deposits 3 542 
Tokewanna ............ Boa nacasaAaaaeasooas 150 | Pliocene of Boise Basin ............-..-.------..-00 : 440 
PTinity <2 32 -.20.2 ce encccese cece nee ee renee 667 Cheyenne Lake. 2-2-2. -2-<2<.c- SAOCSSEO 455 
Tulasco. ---202, 216, 610 conditions at close of 488 
PE WAIWsian. ceewusesan's saocs pence tee eeene ates 229 conglomerates, Big Thompson .- 431 
Utes a.itecn nov cccacaaestaas seen aeeeetee 145, 179, 180 Sybille 431 
Whitehead ~ oc... s.ccsscceas cae ceeeee eee 582, 583 Great Basin, vertebrate fossils in 443 
AMPA 22-2. 22 semen nan sees coat ere ne eee -——s 141 427, 428 
Peaks, rapid degradation of ............. 472, 473 Humboldt group. .--....--..---- 434 
Peak topography the result of névé erosion......... 479, 480 Niobrara group. .-. Sees 425 
Peavine Mountain, Archean rocks of ..........-..-- 97 North Park group .......-...----- 431 
quartzites, Archwan............. 97 of the Plains, vertebrate fossils 430 
Pormatitey: ooo sc case --csan ene cee ee ee 38 Thyoliticstults so ses<s—ecteseese sees ee 438, 592 
in granite of Cortez Rango .............. 7 Sunke! Plaine acn-asecticcacee PAR EoOCO Seo 440 


INDEX. 795 
Page. Page. 
Pliocene of Tertiary ..--.--------+----+--20r sett 425 | Pyramid Lako ..---------------eerene centr 441 
vertebrates, Bone Valley -- 439 change of level of 505 
western Nevada ..----------+----------- 440, 441 chemistry of. ------- 509, 510 
Pliocenes of Humboldt and Niobrara, their faunal region, thinolite of ..----------++++-++ 515 
identity..--.--.---------------2---seerr ann ose ao 439 trachyte of ....--------+----- 602, 603 
Pogonip Ridge .-------------+-------7--" a ise | Pyramidand Winnemucca lokes,nature of solution of 519 
Point of Rocks, Laramie Cretaceous. --.- 336 
Pole Creek Lodge, Triassic..-----------------+--777* 254 
Porphyry, dihexahedral quartz crystals in.--..----- 23 | Quaking Asp, Fox Hill Cretaceous. .------------+--- 324 
Possible outlet of Lake Lahontan .--..-------------- 505 | Quantitative order of voleanic rocks .--------------- 680 
Post-Carboniferous orography. ------------+--+----7* 731 | Quartz, dihexahedral crystals of, in porphyry 2 28 
Post-Cretaceous disturbance, result of.--..---------- 444,445 | Quartzites of Medicine Peak.----. -------- 55 3k 
orography ---------+---+-+2+7-20777" 746 Weber, O-wi-yu-kuts Plateau. . --. 148,149 
Post-Eocene orography mentioned. .-..-------------- 541 | Quartzitic schists, Humboldt Range -------- -------- 65 
Post-glacial orographical action. .------------+------- 492 | Quartzose propylite of Washoe..--..---------+-+--+---° 556 
Post-Juraseic orography ---------------------777077" 732 | Quartz-propylites 
eruptive rocks connected Quaternary .--.-------+-----2srerseett 
Withee ee eae ea elen l= =' 546 climatic oscillations of 
Post-Palxozoic orography mentioned ..------------- 536, 537 deposit of internal Cordillera valleys. -- 460 
Post-Pliocene cafions ..-- --------------e2r0trr ttt A487 divisions into Upper and Lower .--- 483, 493, 494 
disturbance of Great Plains --- 488 general features of, in Cordilleras -.---- 466, 467 
formation of glacial lake basins. . 488, 489 general remarks ...-.------------+----- 459 
orography.-------------+---- 542 lacustrine, absence of, east of Wah- 
tilting of, Niobrara group - 427 satch...---------- --- 483 
Powell, Maj. J. W -- -148, 290, 331, 445, 448, 478, 548, 633, 735, 749 lacustrine terraces of - 
Pratt, Archdeacon...------------++--++srerrerrtt 705 LOwer.----- ------ owen ne ene e eee eee 
Pre-Cambrian erosion...----- ---------+-+++7777077" 22 Lower, fossils 
topography. ------ 122 | mountain topography of -- --- 
Wahsatch Range....------------+--- 44 | subaerial..-..-.-----------2 22-205 20 oe" 
Pre-Miocene geology, Oregon ..-------------> 451, 452, 453, 454 talus-slopes - - 
Prescott, Arizona, specular iron schists of ..-------- 105 | Quebec group .-------------+--2-22205 cote ner nese 178 
Present distribution of perpetual snow.------ 462 fossils.....----+-------- 22 eee een nnn 188 
Present rise of Great Basin lakes .-- --- 525 Ute Peak 180 
Pressure-gradient, terrestrial .......---- 702 | Quebec and Lower Helderberg fossils.-- ----------- 192 
Problem of volcanic fusion - ------------- : 696 | Quiednanove Peak, glaciers (extinct) Olfe-seene == 476 
Prilss, palagonite analysis by---------- --------7-7" 417 | Quien Hornet Mountains, Green River group of ---- 390 
Promontory Range, Wahsatch limestone Ofeeeree aan 196 Vermilion Creek group of 368 
Propylite .--...---------+---++-2 2000 _. 545,550 | Quinn’s River sink, efflorescence of 514 
(augitic) Silver Mountain ----- = 554 | Quinn’s Valley, rhyolite of .----------- ------ 648 
Truckee Caton ..----- .. 553, 554 
Berkshire Cation, Virginia Range ----.---- 554 
Boon Creek, Toyabe Range .-------------- 552, 553 | Raft River Mountains, Archean of ..----------+---- 54 
Cortez Range .-------------------++0rre7t* 552 Citadel Peak, granite of. .--- 55 
Fish Creek Mountains ..-------------+---- 552 | Ragan’s Creek, basalt of 664 
Kaspar’s Pass, Montezuma Range -.- 553 | Ragtown, Soda lakes....-------------+++--270700077" 512, 513 
most limited of volcanic rocks. ------------ 551 | Railroad Cafion, basalt of --.-----------++-----+7-77° 660 
(quartzose) ..--.-----------+2+2++--0 20077" 557 Wahsatch limestone in --.--------- 209 
Cortez Peak 558, 559,560 | Railroad Peak, rhyolite of .--------- .. 622, 623, 624 
Cortez Range 557, 558, 559 | Ralston Creek ....--------2-----02eeeectes rr 23 
Golconda. ------------ .- 56(,561 | Rampart, The, basalt of..----.--.----++--+-+-507777* 654 
Tron Point .-.--.---------------+ 560 | Ranges, Aqui 185, 186 
Papoose Peak..---.-----+------- 558, 559 Augusta ...---------------- --2----== =-="=" 564 
Wagon Cafion 558 Cascade..-.---------------ee2-- eer 452, 453, 454 
Steamboat Valley .--.------- ----- 534 Colorado. -. -5, 6, 17, 18, 19, 21, 22, 23, 24, 28, 104, 132, 133, 
Virginia Range ------------ 555, 556 134, 249, 250, 292, 299, 305, 467 
Washoe. .----- ceeeeeeereeee -550, 555, 556, 557 Cortez ..----- 70, 71, 72, 73, 74, 219, 552, 557, 558, 559, 563, 
Propylitic tuff, Daney Mine, Washoe 550 566, 567, 574, 620, 621, 660, 661 
Protogenoid granite of War Eagle Mountain.....--- 105 10} VY pepe EOS IEHOOODII CUS OSE OESION ... 393, 616 
Province of western Nevada Triassic ..------------- 266, 267 Gosiuteceencessecenene=-l-===" . .5T, 216, 217 
Provo Beach. .-.------------ ceencn eens 492 Granite .....-- 600 BE ee eee ae 00) 99) 08 
Provo Valley, trachyte of ..----------- Havallih)-c------------- 81, 82, 83, 87, 280, 281, 600, 636 
Pseudomorphic chlorite after garnet Humboldt ...----5, 12, 62, 63, 64, 65, 66, 67, 68, 69, 70, 85, 
Pumpelly, Raphael ...-----------+--++-++reereest eee 86, 393, 475, 476, 502, 614 


Purpose of this volume ...----------+----++--7-"""" 
Pyramid, thinolite of tho..-.-------+-+++++++reseeee* 


Take coesesasccecesee=) @a===s5=r--—=en- 96, 97, 515, 601 
Medicine Bow - ..7, 20, 28, 29, 30, 31, 36, 135, 250, 310, 407 


796 INDEX. 
Page. 
Ranges, Montezuma.....- seccescessecerss 87, 88, 89, 90, 642, 667 | Rhyolite, Antimony Cafion .......... etait 
Ombe...- .-- 56, 57, 608, €09 | Augusta Mountains 
Oquirrh. . -213, 221, 393, 590 Battle Mountain ....... 
iPah-taon-sesceceeesen ee ace oe aaneeee eee ees 91 BaylessiCanion\ on. <2 oe eae eee ee 
Pah-Ute .....-.. 83, 84, 85, 278, 279, 600, 637, 638, 664, 665 BOGNLY CS aioenjam Sosan em eieesea sen netceeeee 
(Parkmeasacs = asasane --5, 7, 20, 21, 36, 37, 41, 259, 303 Berkshire Cafion ....-... 
iPeoquopiss.sscssee- ---- 58, 200, 222, 391, 392 Black Caton ....... Scetee : 
PEN Olean seat 189, 190, 193, 194, 596, 620 Black Rock Mountains. . ---- 648, 649 
PLOMONtOLY, son atensanicais caa|sestestiaatsiasicisaa a 196 BonewWalleyeesesesseaseaten cases ees 617 
Riverses-cs-s-ese eae eee 117, 392, 572, 616, 617, 618 CaricoWbake)-...ncmeccesiscasenlcleseeecers 622, 623 
Seetoyarccc-ccacecesneecocs 74, 75, 211, 573, 596, 618, 619 CarlintPeakstc.cos.ccennaeecaces cecteeeees 621 
Shoshone .......... 77, 78, 219, 220, 622, 627, 628, 629, 662 ChatayalReak, 2c. scare -shaceeeattanstaesee 640 
Toyabe .... 75, 76, 481, 552, 553 Clan:Alpine!Canion--nc.<<ccsisenssacisceemsl 634 
Truckee: 2.2.5 scsccececvcccties soee 94, 95, 650, 672, 673 ‘ClurosHiill sy oee ee siee senor e 621 
Tucubits' =. <.s\cce=sessninecess scissecemecnsae 201, 218 Cortez: Pealkeccesscccseccessneenesteeee =i Ol l O28 
Winta---.-- 8, 9, 10, 42, 43, 139, 140, 141, 145, 146, 148, 152, Cortez Range........ 321, 620 
153, 154, 259, 290, 291, 303, 314, 463, 470, 472 Cottonwood Creek 639 
Waka. oso 1cecss- cas eeete nace eee eee 33 Dacey’s Cafion........... 635 
Virginia ........515, 565, 566, 567, 569, 570, 571, 602, 603, Deep CreekiValloyi-.--svsesseateneeeeeeee 611 
650, 651, 676 Desatoya Mountains ..............-..----. 630, 631 
Wahsatch......-. 8, 44, 45, 46, 47, 48, 49, 51, 52, 53, 85, 86, Desert Buttes iaaesc ces <ctee nee wen eeee eae 608 
87, 154, 155, 173, 187, 188, 197, 200, 202, 203, 206, Desert!Gaps.-<c-c--ces seca eee ee 610 
207, 264, 265, 268, 293, 472, 483, 500, 586, 590, 591 distribution and age of .. 606 
West-Humboldtwea.ocsoecnas se eearee eee 476, 640 Egyptian Cafion 615, 617 
WihitO:Pine-ccccs co seo cce Seep eer onsenee 187, 188 Hl koiRan g6cmcenn eres. eee eene se neeeee 616 
Raven's Nest Peak 189 near) Evanston. 222). .).s5- 0st sseee neces: 608 
Ravenswood Hills, rhyolite of..........-..... .----- 628, 629 Fish Creek Mountains .................--- 632, 635 
Iavenswood Peak, Shoshone Range, Archean rocks. 78 Forman Mountain 649 
muscovite in granite in.......... 78 Fountain Head Hills. .. 610 
Rawlings Butte, dioritic gneiss ...............----. 42 Granite Point ....-.... 634 
SULA LOSSIIB 22ers keer ececaescner 290 Grass Cafion = ss-2.n2sccc vancadeeseaeieceeee 646, 647 
iIPalmozoiciOf.sceeses-scecceseccese= 136, 137 Goose Creek Mountains .............---.- 610 
quartz of dioritic gneiss, inclu- great chain of middle Nevada. 615 
sions (fluid in), with salt cubes... 42 Havallah Range ......-..- 636 
Rawlings Station, Archwan Rocks of ..........----- 41 Holmes Creek Valley. . 610 
Recapitulation of Cretaceous 347 Jacob’s Promontory ..... 329 
Mesozoic 340 Jacobsville 627 
Silurian Ute limestone . 231, 232 Kamma Mountains .- 648 
Upper Coal Measures...........-. 241, 242 Karnakcses «scceseceeees 644 
Recent: periodia--oca= cana <yeoa- ae cciseee aEBECHE CSCO 459 Leach Spring ..-...-.-.. 613 
Recession and distribution of glaciers (extinct) ...-. 461 Lovelock’s Knob 643 
Red Buttes Jura 288 Maggie Peak .---s5.ssenoeecense Soeeicnae 619 
Red Buttes Station, Dakota Cretaceous ... ce 300 Mahogany Peak ... 613 
had Creek... s-ectsasescascsassanicsteamenten 42, 43 Mallard Hills ..... 615, 616 
Red Desert Station, Vermilion Creek group of - . 364 Montezuma Range..... 642 
Red:Dome;| basalt of; /. 24 c.cc-.ssceuccccscsecceucus 658 Mopong Halles ote scs.cccesmcenec cesses 640, 641, 642 
Red Rock Pass, Bonneville outlet .............-..--- 492 MotUnt*Airy casawsliecieesose = scse eee ens 627, 629, 630 
Redding Springs tufa................. 495 Moses .. - - 632, 633, 634 
Reed and Benson Mine..............----+s 177 NOVA \ocelonacneiie coe siteeeee eee seee 625 
Reese River Valley, trachyte of. 600 Richthofeno co ocosenscebinceasanens 607 
Relation of Archwan to later rocks, Humboldt Range. 62, 63 Lie ao 5oca con SCO DEE aBeno aS besos 625 
and Palwozoic ..............2-- 122, 123 Mullon’s' Gap eewsecccasiseccescbcece ce scece 650, 651 
Laramie and Eocene 444 Nannie'’s Peak 617 
Mesozoic and Palwozoic 342 New Pass.. 631 
Permian and Coal Measures 343 Ombe Range. : 608, 609 
Reno, infusorialisilica of-- sass dssecescseeeeseceenees 419, 420 Osino CATON eweniecciscousjessemacnseselceeees! 617, 618 
Result of post-Cretaceous disturbance ...........--- 444, 445 Owl Butbereaonsse cn civacenciceeecscceekceeee 608 
Résumé of Archwan geology Owyhee; Binfis ees ne cce eb acaseeneseae 624 
Cretaceous: asco. smcesrescceeeee (Pah-keah Peaks cccpeccccec ssn ccessecteceee 645 
stratigraphical geology (Pah-tson Mountains /--<--cicosseseee acess ce 645 
Tertiary lakes ............ Pah-Ute Range. cc. cenco- ose eaten ce 637, 638 
Weber quartzite .......... Passage Creek: :...+.ac2<c2cssdeecesten oer 610 
Rhodes’s Spur, Paleozoic of....... Poko: Pealizsscce ees dee ee eee 617 
Rbyolite; Aloha) Peak. oc: .tossceaaseee enone meee Penn Caiion, River Range. - 617, 613 
Antelope Hills ................ 4 Pine Nut Pass -.2s<5--25/<c0- eoseeeeeeeee 620 


INDEX. 797 
Page. Page. 
Bhyolite, Pifion Pass ..----- oop cctcecectes~=s, 619}620 Rocky Mountains. ....--------++s--sercrtrereerr 127 
Pifion Range.----------+ +2772 22 re 620 the term ..-..--------------- 5 
Quinn’s Valley. ------++-+--+++-*-- aes 648 Archean of, evidence of age - QL 
Railroad Peak ..---------------77 00777" §22, 623, 624 orography of...--------- TR9 
Ravenswood Hills - -- 628, 629 pasalt of.--.-------- 654 
River Range .----------------- apsooa 30 616 Dakota Cretaceous 
Rock Creck Valley ----------- Sacecoenooen 626 Jura --.--- 0-200 - eee eer eeee 3 
Ruby group ---------------"- 613 frost disintegration of 472 
Sacred Pass, Humboldt Range ------------ 614 Paleozoic province of ..---- Soe co 127 
Schell Creek ..--------------- 611 terminal moraines of.-.------------ 473 
Seetoya Range..-- 618, 619 topography, Archwan.----- 124 
Shoshone Mesa -- 624, 626 trachyte of ..---------+-- . 579,585 
Shoshone Pass ----------- i oeccsesconanss: 632, 634 Triassic of .------- aaa 249 
Shoshone Range -------------- . .622, 627, 628, 629 | Rose Cation, trachytes Of. .---------++e+r2220- 000777 590 
Shoshone Springs --------++------r97"777" 634 | Ruby group, basalt Of eenaae nen eeeaasen=ssaeenen==s 659 
Sioux Creek .-------+------- Deseeeencnese* 607 rhyolite of...----------+--+srrereetrt7 613 
Soldier Creok - 624 Wabsatch limestone in 203 
Sommers’ Paes.- 639 | Ruby Valley, hot springs Ofe se cccescoccessaciso==e 503 
Son Hot Springs 638 
Spanish Peak 651 
Spring Canon, Wachoe Mountains -------- 612,613 | Sacramento Cafion Trias. 
Squaw Valley ------------e+-s-70r7-7777" 625,626 | Sacred Pass.---------------20 72-7777 so nono" 
State Line Peak ..----------+--++---- 650 Humboldt Range, rhyolite of - 
Susan Creek 619 | Sahwave Mountains, dioritoid granite of . - see, 96 
Table Mountain .---------- 639 | Sam’s Station, infusorial silica of..------------------ 419 
Truckee Caiion .----- ------ 651 | St. Cassian group ----------------- 269 
Truckee Range ---------- co 650 | Saline deposit, Crescent Valley .------------------7" 503 
Truxton Springs, Arizona .----------- 649 efflorescences .-----------------77770 0007" 498, 499, 500 
Tucubits Mountains ------ Soneesesece==—== 610 of Bonneville area 501 
Tulasco Peak ..-----------e2-- 2000007077777 610 Eagle Valley E 502 
Tuscarora ..----------eeee errr 624, 625 Lahontan...-.--------------- 513 
Valley Cafion.----------------s-re0terr 7" 634, 643 Maggie Station. 313 
Virginia Range ---- 650, 651 hot springs, Wahsatch Range 500 
Wachoe Mountains .---------------* - 611 | Salines, middle Nevada 502 
Wahweah Mountains ----------- - 622 | Salt Lake Basin, Weber quartzite --- - 214 
Warm Springs.----- wnccecenes _. 626, 627 | Salt Lake Desert..-----------------r0r-re 207 12 
West Humboldt Range ----- 5 640 region, Wahsatch limestone ofiae-es 200 
White Plains .--- 644, 645 fluctuation of level .--.-----------+-+---7* 12 
Willow Caiion -- 636 spherical sand, carbonate of lime of. --.--- 501 
Winnemucca Lake...--.----- 650 | Salt Lake Valley.-.-----------------7777-""" 11 
Rhyolites, their relation to basalts ..---- Seenecesae= = 687, 688 | Salt Lake water, analysis of, by L. D. Gale -- 497 
succession of. .-.----- -- 686, 687 chemistry of. -------------- -- 496, 497 
Rhyolitic tuffs..-------------- 438 compared with Dead Sea .--------- 497 
Pliocene age of ...--------------7777" 592 lithia in ......-----------------+2°°° 496 
Richthofen, F. von ------ 549, 550, 554, 649, 681, 682, 687, 629, 707, | Salt Lake and the Promontory, Archwan rocks of... 54 
710, 711, 716, 721, 722, 724 | Salt springs: .------=-------2-2- rennet 499, 500 
his volcanic classification -------- 549, 550, 682, 683 | Salt wells, Laramie Cretaceons ----- -------------7 336 
Richthofen’s law..-.--------------eseerser rere 681, 682 | Sand, spherical, carbonate of lime, Salt Lake .------- 50L 
Rise of Great Salt Lake --..-----------+++-7-- 00777" 505. | Sand(@unes .--+-------- ---------<--- nen ooo ns 528 
Owen’s Lake. ....----------2 002-77 070°* SonTs 525 | San Gorgonio Pass 507 
River Range, andesite (augitic) of ..---------------- 572 | Santa Clara Cafion, Koipato [rias.-+<--s<--'=- 273 
Green River group of .---------- 392 | Santa Maria River, Arizona .-------------- 105 
Penn Cafion rhyolite of... ----------- 617,618 | Savory Plateau, Colorado Cretaceous .---- --------- 313 
rhyolite of ..---------+---2+eerttr ert 616 North Park group of.-. 434 
Weber quartzite . 617 | Schell Creek, rhyolites Of ecto ceeeeatten= cs s-=* 61 
Rivers of Lake Lahontan...---.-----+-----**777777" 504 | Schell Creek Mountains, Cambrian shales of...----- 186 
Roberts Peak Mountains, Cambrian and Silurian of. 191,192 | Schists, spotted, near Irish granite, mentioned by 
Roches moutonnées, Uinta Range 472 Haughton ...------------+ s----2eerersoone nono 719 
Rock Creek..--------------+270-0000 7" 309 | Scrope, Poulett..----------------srrsrrrrrt 705, 706 
Colorado Cretaceous .--------++--++-***- 310 | Section, Paleozoic, Wahsatch .------------*---**77>" 154, 155 
Fox Hill Cretaceous .-.----------+------ 327 | Section Ridge, Trias...----------+----srrrett et 201 
Valley, rhyolite of --------+----++------* 626 | Sediments, subsidence of -----------+-----*> 115 
Rocks, Plutonic and volcanic, differences of .---.---- 206 | Seetoya Range, Archwan rocks of..----- 74, 75 
Rock Springs, Fox Hill Cretaceous ------+----+-+--- 324 Coal Creek, trachyte of.------------- 596 
Rocky Creek, Basalt of ..-..------+-+eresters seer 664 granite porphyry O) Ba mato: aeabeseoo 75 


798 INDEX. 
Page. Page. 
Seetoya Range, quartz of granite, inclusions (fluid) Slope of the Great Plains, Niobrara group of ....... 426, 427 
with salt cubes in.........-...--.- 74 | Smith, J. Lawrence, analysis by 499 
quartz with granite porphyry inclu- Smoky Valley, alkali flat of ..... 503 
sions (fluid) with salt cubes in .--.. TAY | SEV CHOP OY S53 e ha -emaenocsssaassemnemcaececeace 592 
rhyolite of......-...---------------- 618,619 | Snake Plain, Pliocene of .._..........--.-.-.25-..--- 440 
Susan Creek andesite (augitic) of... 573 | Snake River; redigneiss of --.-----.-----_ses---oesee 41 
Wahsatch limestone -......-..-..--- 211 | Snow distribution of Glacial period..............-.-- 477 
Weber quartzite of..... ~ 219 erosion, peak forms due to..-.......-.-..-.---- 480 
Separation Station, Laramie Cretaceous..-.-.--..--- 334 line, downward encroachment of .........----- 526 
Sepiolite of Paris Basin........-.---.--------------- 116 perpetual, present distribution of ...-......--. 462 
Sheep Butte, Colorado Cretaceous 313 | Soda lakes, Ragtown, Nevada ...-.... --510, 511, 512, 513 
Sheep Corral Caion, trachyte of ...---- .. 603,605 | Soldier Cation, Weber quartzite of .........-...----- 213 
Sheop Creek, Jura..........----------- 291), | (Soldier|Creek, rhyoliteof-.-4-ssesey meee eases esse =e 624 
TTIAG)-\o\-s~ cies sacs ca'smne sine cenmncinele cic 260; 261, |; Sommers? Pass; rhyolitolofcena--eseaa- saat e ae scaas 639 
Sheerer, mentioned 1145 eSoutSprings basal viotseeastessseseee nen eecasetescen 664 
Shoshone Basin 592 Thyoliteiofsccsase esac eeaaa see aes 638 
Shoshone Falls 592 | South Bitter Creek, Vermilion Creek group of .-.--.. 365 
Shoshone Lake 456 | Spanish Peak, rhyolite of 651 
457 | Spaulding’s Pass...........-...-.- 278 
Shoshone! Mesa: esn--c-s-oc en cveseetenn= = slemas= meer 662, 663 | Specular iron schists, Prescott, Arizona....-....-..- 105 
rhyolite of.. -- 624,626 | Split Mountain, Trias.............- Gescéoccoocoscess 261 
Shoshone Pass, rhyolite -- 632,634 | Spriggs coal mine. .............2---..-----eeeese- == 317, 318 
Trias ....- BO 281 Fox Hill Cretaceous .....-....-.. 328 
Shoshone Peak, dacite of.......-..-.--------20------ 5684569!) (Spring Valley Pass, ([rias)---..2---------sa=—=—=ce= =< 270 
iaciers| Of. conc csecseseces-no=s'e-=0- 476 | Spruce Mountain, basalt of ...-.-.-.--..------------ 660 
Shoshone Range, Archean rocks of .. 77, 78 Wabsatch limestone - 200 
basalt of --- 662 ; 
granite of ...-.. SSS CHB SSCS CCEA cic 
Ravenswood Peak, granite of ..-.. 77 | Stansbury 
Archean rocks 78 | Stansbury Island, Wahsatch limestone of ..-.....--. 199 
Archwan Stanton'Creek, Trias). .2--\sescesacmaessnass—e 264 
schists of..-. 79 | Star Cafion, Koipato, Trias... 273 
rhyolitojof ----<.---.-<.-=-- 622, 627, 628, 629 | Star Peak group ........-... 347 
Weber quartzite of ..........---.- 219, 220 AMEE nee Socmacepacecocacinecderencecs 270 
Shoshone Springs, rhyolite ...-.-.-...-------------- 634 | State Line Peak, rhyolite of ........-.- Soressacaosss 650 
Mrigsicco=-acaeeesices 281 | Staurolito in schist, Garnet Canon, Uinta Range - 43 
Shoshone Valley, basaltic plain of...-.--. 679 | Steamboat Valley, andesite (augitic) of. - 576, 577 
Sierra Nevada ---<-..-2<0nnsceee==0= 452 propylite\of-<-----.- <2... 554 
glaciers Of ..........-0-22200-see--050 463 | Stevenson, J.J. ......0-- --< 200 caneaeencenecseenes--- 331, 332 
mountain disintegration of........... 472 | Steves’ Ridge, trachyte of .........------547, 581, 582, 583, 584 
talus-slopes of ......-----------eee--- 485 | Stockton, Green River group of. 393 
Signal Peak, Trias .......-.--..----+-----+---+sseeee 280 | Stokes ....-..---....--..---- 705 
Siliceous schists 34 | Stony Point, basalt of. - - 663 
Silurian (Niagara) fossils ...... OS40 StOppalll aaonsee ace ese ates sa aene nner ecs= eee nee 706 
(Quebec) fossils ...-..--.-. 233 | Strata, contiguous, absence of chemical action be- 
Uteilimestone>..-2s----ssesesese- cere ==--—= 175, 176 tween, in Archwan beds .......--.....--.-0--+---- 112 
City Creek Cafion..-...--..- 173,174 | Stratigraphical geology, résumé of..-...... 531 
Cottonwood section .....-.-. 167, 168 sections summed up 542, 543 
recapitulation......-... .-- 231,232 | Strong’s Knob, Wahsatch limestone of .--..--.------ 200 
Weber Cafion section ...... A 157 | Structure, microscopical, of thinolite........-.-.-.-. 517 
White Pine’ Range) <<: --<.cssece-e=se=—- == 188 | Subaerial Quaternary -........------------ 484 
White's: Ranchiass.ceccessceceoseescen= Sach 192 | Sub-Carboniferous, Dry Cafion .--..--..---- 197 
Silver Creek, Miocene of. .....--.----02- cesses ece--+ 414 fOSSUS eases semaines cient é 238 
trachyteOfs-ccsccecsecesese easecene sma 588 | Subsidence, two types of.....---.. .--.-----+---+---+ 732 
Silver Mountain, propylite (augitic) of .....--....-- 554 | Succession of andesites.....-.-.....---------+-++--+: 684 
Simpson) cose. cose as-satccashenestesaciecieaseiceeancs 1 trachytesi.--s-cmcesa= socio —=—= 684, 685, 686 
Simpson's expedition ...................cccncceccece 211 volcanic rocks ........---.----- - -683, 624, 687 
Sioux /Creek; rhyolite ofi-<----2---cossccesencscecoe= 607 | Summit Spring, Trias...--. Aco 280 
SiouxtbakesMiocenoss<--nss.scceccess ceceteoteescceae 451 | Summit Valley, Uinta.........--.....---------+----- 145 
distribution of .........-.------ 451 | Sunny Point, Green River group of ...-..----------- 385 
Siskiyou Ranges. 9c=--se+ccataaeeeeaccceeacesacs Susan Creek, rhyolite of 619 
SkolligstRidget:---- cases ceanaceesaseenanesecen=s == trachyte of 595 
Skull Rocks...<..5.....-... Sybille, Pliocene conglomerates of. 431 
Slater's Fork, trachyte of.. A Syenite, Cluro Hills...........--------------2--2++- - 172,73 
Slates on French Creek ......5.....-cccccccccccccncs Park; Range). -cccnescoesscacencrleccaseasi=-=— 40 


INDEX. 799 
Page. Page 
Table Mountain, basalt of..............--- Saas ee eee 664 | Trachytes, Aqui Mountains ...............-.-------- 593 
rhyolite (ofe-sece-senceaeeeseneceas 639 Astor Pass....-..---- C02 
Tabor Plateau, Green River group of..-........---... 387 Bonneville Peak 593 
Vermilion Creek group of. --. 368 Cave Springs .----- 595 
Tabular statement of Palawozoic subdivisions. . Cedar Mountains .............-...--..--. 594 
Talamantes Creek .-........-------.----00s =o Chataya Renkieere=slaneea=-ens eee =e le 600 
Talus-slopes of Arizona .............-..0-----. neces City Creek, Wahsatch .............--..-- 590, 591 
Oh CAliOnia jac. sesanen a= eseoeaee eee Coal Creek, Seetoya Range. .-.-.---.-.--- 596 
formation of - Cortez Mountains..-..-. 598, 599 
OfeNOVAGS ace essscessee=e= Crescent Peak==--cssne-ssens-o2-" 581, 582, 583, 584 
Quaternary of.-...- wderreece--- > Davis Peak -....-. Be eee ee 581 
of Sierra Nevada. .........--......----- 485 distributioniofesscssesos-sio=so-seesee ees 578, 579 
Tebog Peak.....--.-----.----++---22 222s eeeeee eee 640 IDS SEN cece eeconoceasose Snquetcoss 597 
Terraces, absence of 484 Dixie sPasseteee sees nena senna etesenee 596, 597 
in Cordilleras ....- 466 Hast|Canotessssceeesaaseaseseaw ase 589 
height of, Lake Lahontan...-. 518 Elk Head Mountains .- «aeece= OGL, 082, DES: 
lacustrine, Quaternary.......-----.--.---- 488 geological connection of. ....-.---...----- 579,580 
TakesbonnevallOs ess sacs sees eran s soe = Han tak etkessen-mosaes cher sae 582, 583, S84 
Terrestrial heat-gradient. -. Havallah Range - ze 600 
pressure-gradient. Heber Cain... 587 
rigidity ...-...- Heber Peak .........- 586 
Tertiary lakes, résum6 of...--..---..------------+-- Henry Mountains, age of......-..--.----- 548 
table of Undian/S prin geese .eos en eae ee ena ee nee 
orography ----- Jacob's Promontory - - 
yoleanic rocks Jordau Valley ..--- 
and Cretaceous, Great Plains, age of. Kamas Prairie .-..- 
Thingvellir Lake, palagonite of. ......-..-.---------- 417 Kamma Monntains ......-.....-.----.--. 
WEST nae ce coseca nes aeHe sacra aes Soon Dens Seccrs 508 Kawsoh Mountains ......-..-----.------- 
‘Anah6 Island’< <2. <-2--5..--- 515 Lake Range 
botryoidal surface of..-...-..-- 517 Medway 
chemistry of ......-..-.-..--- 518 OquirrhtKan2@s—- oe esscaneeosea=oe === 
crystals, gaylussite. ........-..------------ 517 Ormsbyihea keer sa.-=eae aaa 
distribution of .--.. 514 Pah-tson Mountaina.-.-.......-..-.-------- 
GTNED Spe dccaecte Ssodeccocshoeenaadccans 515 Pah-Ute Range ..-.. 
Lake Lahontan ....:....--..--------c-00-- 514 Palisade Caiion .. 5 
Lake Range. .......-------- 515 Parkview Peak -. - 580 
microscopical structuro of. - 517 Parley seal ksweene=eeeeee ae eccee se iese ee 586, 587 
octahedral crystals of ...-..-- 517 PeoquopiCreeks-.-s--eseceuns ss eeneee sane 695 
pseudomorph after gaylussite..-...------.- 518 Pilot Butte. ....-- -- 585, 586 
thopeyrarid one aseoericeeeceee= ace as mms 515 Pine Nut Canon . 600 
Pyramid Lake region 515 Pifon Range. .- 5 596 
‘Truckee Valley ....-.---.-- 516 IPLOVO CANON eeesn sea eeatanne tea mane 58 
Virginia Range .......-.- 515 IPTOVON Gl lOyoe nase eames eee 587 
ThomBon! sAames esses os aee = 2 eae Sos. noe esse see 704, 728 Pyramid Lake region. - 602, 603 
Thomson; Sir: William... --<-2-22:----0--2+s--=-- 696, 697, 701 Rocky Mountains......--.------.- - 579, 585 
Thousand Spring Valley, Humboldt group ----.----. 438 Rose Caiion ..-.....- 5 z A 590 
Tim-pan-o-gos Peak, Paleozoic of ......-...--------- 172, 197 Sheep Corral Cafion............-----..--- 603, 605 
Tiraks ysl AlGaAs = sae ese aoe ca seca a's =e 262 Silver Creeks /.cos=--aeesen==Seennnen ane 588 
Titanite in granite of Wachoe Mountains .......--. 60 Slateris hotkses--ceeeaseae ease seeneceoes 585 
Toano, Upper Coal Measures of......--..--.-------- 222 Spake Cavoneenassscassa-\sae==<eann==seome 592, 593 
ean OV PASS ee meeee ee ease sa=aeioes= == 221 Steves’ Ridge. . --547, 581, 582, 583, 584 
Hamboldt group of 438 Succession Of... <2... <2 222. cons ennnn= 684, 685, 686 
Topographical methods on Fortieth Parallel .-....-. 768 Susan Creek ..........---...-+ Sart 595 
Topography, Archean, mode of determining ..-...-. 122 Truckee Canon -.---cea-aqeesc-5--=5 =~ 603, 604, 605 
of isothermal couches.......----..----- 703 Virginia Range. <2... ccc cwenennane 602, 603 
Tourmaline in granite, Crusoe Canon, Pah-tson Moun- Wagon Caion.. 598 
PAT besa sce coccen ace co necnos ser eco anecsnsssao ste 91 Wiahsatehcn-sceccenece= ale 586 
Toyabe Range, Archwan rocks of ------ PP HH] Wahweah Mountains . > 599 
Boon Creek, propylite of. . = 552553: SwWihitehead Peake... -----n-ccceaecerceea= 582, 583 
Dome Mountain, débris of.........-. 481 White Rock Springs ........----.-------- 594 
RTANite Of ae seen/e7aceee aa csaseaeas 75, 76 Willow Creek............------. -- 593, 594 
Park Mountains, granite of........-. 76 | Trachytic tuff ........---.------------+---- 454, 589 
Mracny tes! -meeeenees==secese enone =n ciaee 578 Miocene of. ...--..--.---.. -- 422, 423 
Ada Springs ...--..----- 581 | Trachytoid porphyry-....-.-.-..---------+---0++-+-=+ 581 
Anah6 sland ii2<z<--c-csecevecesccsa=so= 601 | Treasure Hill, Wahsatch limestone of. ...-...-....-. 205, 206 


800 INDEX. 
Page. Page. 
Triangulation of Fortieth Parallel.........-- CopossA 764 | Trias, Vermilion Creek ..........-.....---.--.2----- 259 
Trias, Alpine ..-- -- <22- + e-- cnn nwsicoeewens-= =~" 269 Wahsatch Range - -. 264, 265 
fossils, Desatoya Mountains. . - 283, 284 Weber Cafion ....-.---.-- a 265 
Stargonnoleserecadeses cste=aat 276, 277 West Humboldt Range ............-....-.--- 268 
Ammonite Cain .... Sacaae 283 Wampa'Platean-------0----seceresessrcctesec= 261 
Antelope Creek section .......--...---.------ 257,258 | Trias and Jura, comparison of Eastern and Western 
Anteros Cafion..-.-..----+------++2++--+------ 263 provinces. - 343, 344 
Augusta Mountains. Trinity Peak....... 667 
Austrian Alps... TTLONS NOOR AK Orca neces ieee a ceeeneecleee an eeesee 514 
Big Thompson Creek. : : 252 | Truckee Cafion, andesito (augitic) of..-....--..----- 576 
(Box: Elder|Cation\ace-sencccanceesowccs==---== 255 ass] teeee see enaconsoncledecenien ase 677 
Box Elder Creek section. .........- 251 propylite (augitic) of......-.....-.- 553, 554 
Buena Vista Cafion ...-.........-- 268 Thy telolees s-nae a eeen eee seaaaas 651 
Buftalo-Peaky-cosn-s-cees sot ecaaees 268 trachyteotee= soem ereceeeena se 603, 604, 605 
Cache la Poudre. . onnace 9553 UDruckGe Merry ,seccieceamn(seecars-eaat a censianaciacinaae 604, 605 
Camp Douglas. - oon. coc eccceccersacicecsnn== 265 | Truckee group, area and extent of ...--..--.--- ---- 412 
Cherokee Butte ..--........------ GoceSoenate > 258 Miocene .ofc-ssescensnesso ese eseeers 412, 414 
Chngwater. ..-.-- - 253, 254 BOCtION OL seaees esse ayeannaienesen=e 415, 416 
Colorado Range .--- 249,250 | Truckee Miocene ..--.. ...-..----- -<- 00 ecnncee cen en- 454 
cross-stratification .-. A 344 | Truckee Range, Arch@en. .....-.......-----.---00-- 94 
Dead Man's Springs.........------- PROS OeEEES 261 basalt Ofess— so-so eeecie- ede neeecete 672, 673 
Desatoya Mountains ......0.2.c00---e-0-----2 252 Luxcer Peak, Archzan schists --.--- 95 
ddlomitejseassscorenwecicececesocaccnae= 344 Nache’s Peak, granite .......--..-.. 94 
DuiChesueenaccerescstecrceceesnaciace - 263, 264 PNY OlitO Obes eee seen eee ects er 650 
Dunn Glen... 279 Winnemucca Lake, granite near -.. 95 
Elk Mountain. - O580l PTrnckee ni vVencass- a2 secant ele enn eee 13 
Escalante Platean .- 261 bifurcation of 405 
ish’ Creek Mountains: ..+ ..00ea<-0-css~cnnee= 281 | Truckee Station, basalt cf .- 676 
Flaming Gorge. ......... 202 --secsccsesccnenes 259,260 | Truckee Valley, thinolite of........--.-------------- 516 
fossils =-s<se. foe 344 | Truxton Springs, Arizona, rhyolite of....-..---.----- 649 
Geode Cafion . .- 262 | Tucubits Range, rhyolite of.........---.--------+--- 610 
Golconda Pass. . = 220 Wahsatch limestone of .----..----- 201 
PV PSUM a - cecscecosemsaessecescrecssess-== 253, 256, 344 Weber quartzite in ...-...-- 5 218 
HavallahtRanges---s-scerssssenveesscossace=== 280,281 | Tufa of Lake Bonneville........-------------------- 495, 496 
Horse Creek --. 252 Haketlahontalicccesssostcetaaceere=ceeesees 514 
Jura series. .. --- 537, 538 Redding Springs ........---.---------ee+e-- 495 
Kamas Prairie - O64))|"" Tolascowbeakyassc ccs oe tees tees aceee an = saan 202, 216 
Koipato group. .--.-......-...--s- 269, 270, 276, 279, 347 rhyolites of .........---.----- 610 
Buena Vista Cafion ........--- 273 | Turtle Bluffs, Bridger group of ..-.--.----- 402 
Coyote Cafion ..- 30 273 | Tuscarora, andesite (augitic) of. 372 
Indian Cafion <-<-<....c.ccne-~ 272 rhyolite of <---<2<js<<¢-s-s-co7---seeleesens 624, 625 
Santa Clara Cafion . 5 273 | Twin Peaks.......-...---.--0+-+--- sacheceeacancanas 229 
Star, Cafion? cas. cscecess=s=--- 273 
Lodge Pole Creek ...---..-------+----+0----=- 
Medicine Bow Range .-. Uinta group ......------------ 2-222 eeee ee eee ee eens 
New Pass Mines .......-... MintapValleyi.-scesscpsecesaan--—se5==e 
Obelisk Platean .......--.. vertebrate fossils of.....----.-----.---- 
Pah-Ute Range. ...---.-----0.eeceeee eee eeeene White River Valley 
Park Range ....-..--000 -cceescccocececoceces- Uinta Lake:....-.....-.- 
IPOOTIAWccaccscsceasscesess extinction of - 0 
POTPHYTOIdS: -0- 2. cece resceee- 269, 270, 271, 272,273 | Uinta Range........----.-----.---------++ 22ers: 
province of western Nevada .....--.-.------- 266, 267 Archean body of...--..---------++-++- 
Rocky Mountains’. -.....-...--cccccocceserss= 249 Archean rocks of ..-------- 
Sacramento Cafion ..-.....-.-- SHpoCDeBogecEaS 268, 270 Caucasus compared to 10 
Section’ Ridge --2.-.2----+----- 261 Colorado Cretaceous ----.-- 314 
Sheep'Creek-.--2.\.2- 22. scene 260, 261 Dakota Cretaceous .-----..----- ------- 303 
Shoshone Pass....----- 281 forest Olssseea- == ea saan en een 10 
Shoshone Springs 281 freshness of glaciation of - .-- 470 
SignaliPeak(--c.veccs 280 Garnet Cafion, ampbibole rock in -.--. 43 
SplitiMonntain’ s2.c-<csssosscenencscsteseeess 261 Archean quartzites of . 43 
Spring Valley Pass : 270 syenite in schists of ... 43 
Stanton Creek O 264 hornblendic schist . ---- 43 
StariPeak proupiacsccseece-ve seers =sene eae 270 hydro-mica schists in .. 43 
Summit/Springs-.---<ssasceccacsceseascesnsne 280 paragonite schist of. ... 43 
(Uinta Ran geycsss-scccecsiocwnccoceesssicsecees 259 Steurolite schist in -.-.. 43 


INDEX. 801 
Page. Page. 
Uinta Range, Geode Cafion, Paleozoic of.....-. o00o0 145 | Vermilion Creek group, Godiva Ridge.....--------- 366 
glacial erosion of... . 470, 471 Hallvilleecen-seasensecne-== 365 
glaciers of. ...-...- - 463 Little Muddy River 363 
OXtiN Cte ess =ateneaeeeneres 470 Little Snake River -. r 361 
Diab acne seseosbonoedocrsancoccSeasos 290 Mount Weltha........-...- 36L 
fossils ener eee eee oe 291 Navesink Peak 361 
limestones of, and Upper Coal Meas- Otter: Gapiroscsscnsen een sa= 366 
ULOS Of. - -- ooo eannnnjewnsericesscese 141 Oyster Ridge -............. 372 
modern disintegration of peaks....... 471 Pine Bluffs -.......--.-..-- 363 
mountain disintegration ..-..... ---.-. 472 Quien Hornet Mountain ... 368 
Pale0Z010 len. < <= -5-=<1<== Red Desert Station -..-..--- 364 
Permo-Carboniferous. --..-... relations with Green River 
Red Creek, age of ...- group .--- 378 
roches moutonnées ..---..-------+----- Laramie ---. 375 
BBWS Goecaamna secanecosonetasTeooeag South Bitter Creek .--..--. 365 
Vermilion Creek group ...---.- 368 Tabor Plateau ....--....--- 368 
Weber quartzite -..-.-..-..------ 148 7 thickest exposures of ....-. 375 
Unaka Range, Blue Ridge chain mentioned 38 ED CIAS ee eettcneasisee lanes ne 259 
United States Cordilleras, absence of general ice-cap Uinta Mountains ..-...----- 368 
TH) Seoteooeeeeoeceone SenecerSHosticu Seacecatacseunee 459 Upper Weber Cation 369 
Upper Coal Measures, limestones of Uinta...---..-. 141 Vermilion Creek Basin. . - - 366 
Wiahsstchi---c---s---—----0-0 155 vertebrates of. .-----.--- 373, 376, 377 
Upper Helderberg fossils, Devonian 5 236 Wahsatch................-- 374 
Upper Weber Caiion, Vermilion Creek group of..--. 369 Wahsatch Station -.-- 370 
Upper and lower divisions of Quaternary .-.-------- 493, 494 Washakie ....-. 
Utah, absence of Miocene in .....--.------------+--+ 412 Basin. 
Utah, Basin, Niobrara group of .....--.---- --- ----- 435 Willow Creek......--...--. 
WteWuak@ess-sa<<----===5-—=~= : 445 | Vermilion Creek and Laramie, nonconformity be- 
its deposits ...-- 446 tWOCN-- 22.5 -cneen cocne= wne==- ones oantecio aotocec 355 
Ute limestone. ...------- 156 | Vertebrate faura of Bridger group 403, 404, 405 
Ute Peak ..........--..--- = 145 fossils in Pliocene of Great Basin ...-... 443 
quartzitic Cambrian .... .--- ------------- 179 the Plains.......-. 430 
Quebec fossils of 180 Uinta group...-... 407 
Silurian.-.........-.---.-..------ 179 | Virginia Range, basalt of ..-...-.-.----------------- 5 676 
Ute Pogonip limestone, its subdivisions...--.-.----- 193 Berkshire Caton, andesite (horn- 
blendic) of .........-.------se-0e- 566, 567 
Berkshire Cation, propylite of ....-- 554 
Valley Cafion rhyolite ....------------+---+--+++==--- 634, 643 dacite of .......-.-----+---+-+--- 569, 570, 571 
Valley Wells, Miocene limestone of. .---- E 422 propylite of -....----.-------+++---- 555, 556 
Valleys of erosion on Great Plains.--..-- 2 6 rhyolite of .....----..----+s-20----+ 650, 651 
Vermilion Bluffs, Green River group of-..-------.-- 386 thinolite of... 0 515 
Vermilion Creek Basin, Vermilion Creek group of... 366 trach yteSier== accra === - - 602, 603 
Vermilion Creek group .--------------------- 373, 376, 377, 445 Truckee Cafion, hornblendic ande- 
Age of .-.. .---- 5 377 Bites Ofeseeeaisen ee aesenacone === n< 565, 566 
Aspen Plateau cS 370 | Volcanic activity, dawn of .-......---.---+---------- 546, 547 
Barrel Springs. - S55 364 classification, Richthofen’s - 682, 683 
Bear River Plateau ---.- 371 fusion, problem of ....:--.-----------+----- 696 
Bishop’s Mountain ..-.-...-. 368 genesis, Waltershausen’s theory-.-.----- 708, 709, 710 
Bitter Creek uplift..--...-- 369 rocks, classification of .......----.------ 721, 722, 723 
Black Butte Station ---- 364, 365 correlation Of ...-......--.----see20- 678 
Camp Stevenson Roe) 369 difference from Plutonic....--.--..- 706 
Coalville==------=--1--="- =~ 371 fusion Ofseae=a.eassaasace=aceemree 696 
Colorado Cretaceous -....-- 314 general relation of - . 546, 547 
Concrete Plateau ..-..----- 372 geological age of. - 691, 692, 693 
Croydon) --<<-------- C 370 natural succession of ..-.----------- 690 
Diamond Mountain ..-...... 367 quantitative order of....--.--------- 680 
East Cafion Creek ..-....-- 371 relation to Pliocene in Boise Basin -- 592 
Hicho|Cafion. coccccccccccce 370 succession of ......-.------+----- 678, 383, 684 
Echo City ...- 371 Tertiary ....-....0------.----------- 545 
Hocene Of, <2 .cc<--cncc-scce> 360, 361 species, genesis of.......------------+-+-+- 705 
Evanston -..........-------- 70 theory, Mallett's ....-..-----.---+-- 698, 899, 700, 701 
Flaming Gorge ...--..----- 368 
Fortification Peak ....--... 362 
fresh-water mollusks of. --. 373 | Wachoe Mountains, andesite (augitic) 
general extent of ......---- 374 Arch@an ....---2------seeee-ees 


51K 


802 


Wachoe Mountains, hasic granite. 


granite ......----202ss--s52--=-- 
inclusions (fluid) in apa- 
tite Olceeeeee eee een 60 
phlogopite in granite of ........ 60 
quartzofgraniteof, with saltcubes 60 
rhyolites/of---s-cssssesseese= es 611 
Spring Cafion, rhyolites of. ..... 612, 613 
titanite in granite of....-..--.-. 60 
Wahsatch limestone of .- -- 202, 203 
IWIRGB WOLD) coesmactcccesscisercie= i 376 
andesite (augitic) of .........----------- 76 
Wagon. Gafion, basalt ofc. 22 25 ce ececceene------- 661 
(EO IGK) etesapecercsospaSebcocosbasscoc 567, 568 
propylite quartzose of. - 558 
trachytes of .......-. “in 2 598 
rWahsatoh Hmest0ne 2.04 «ssseests sss seca e= eee as 155, 195 
absence of lacustrine Quater- 
MOE CABG Olsesccaseser scm 448 
Antelope Spring .--..--.---- 196 
Aqui Range... 199 
Babylon Hill 206 
black shales of .......--.-.--. 199 
. Blue Ridge ---2-co el - anne ae 207 
Carlint Valley: -----<..6-.5.-<. 212 
Carrington Island.......----- 200 
Cottonwood section.....-. 168, 169, 170 
Dolpbin Island ........-. .-.- 200 
Egan Mountains.-.-....--...-- 203 
fossils in Lower Coal Measures 239, 240 
Gunnison’s Island....-...---- 200 
Hat Island ic 200 
Humboldt Range. .....------- 204 
Lakeside Mountains...-....-.. 200 
Ogden Cation section -. - 176,177 
Peoquop Range ---.--- . 200 
Pifion Range ..-....-... . 209, 210 
Promontory Range ....--.---- 196 
Railroad (Canonysccssesces- <== 209 
recapitulation .......--.. , 236 
RuabyiProup)---- coe<cec. one 203 
Sacred: Pass -.< 0.-=~= 205 
Salt Lake Desert region 200 
Spruce Mountain.........--.-. 200 
Stansbury Island.-............ 199 
Strong's Knob..........-.---. 200 
Treasure Hill ....... - 205, 206 
Tucubits Range 201 
Wachoe Mountains .-- oe 202, 203 
Weber Coiion section.....- 158, 159, 160 
White Pine Mountains ..-....-. 205, 206 
Wahsatch Platend -.-..ccssesecusclocsseeiceae 11 
Wahsatch Range -.......-..-- 8,11 
Archean geology 45 
PATCHRAMTOCKS mmcueeeesieeraeee esse 44 
BoxthilderPenkvcsecteccccstie= sae 181 
City Creek, trachytes of. ...- -- 590, 591 
Clayton’s Peak, granite of....-.... 45,46 
granite porphyry cf 46, 47 
Colorado Cretaceous .......-.--.--- 316 
Cottonwood Cafion, Archean schists 
Ofvrececeeee see 47 
garnetiforons 
schist of..-... 47, 48 
Dokota Cretaceous.........-..--.-- 304 


INDEX. 


Wahsatch Range, débris of -..............- 
Farmington Caion, chlorite pseudo- 

morph after gar- 

netin muscovite 

PNeisseseseeae 

hornblendic 


mMuscovite 

gneiss in..-.. 

OU) becmetetelem arte ai CheaScdaraecescse 
foot-hills, Permo-Carboniferous of. . 
‘PalwozoicOtee-es--.---- 4 


Little Cottonwood Canon, Archasan 

quartzite in 

Little Cottonwood Canon, granite of. 

longitudinal fault .........-....-.-. 

middle, Archzan schists of .....-... 

mountain disintegration of... . 

northern, Arcbzan rocks of.... 

Archean of, relation to la- 

ter geology. .-...-----.. 

Ogden Canton, hornblendic gneiss - . 

zircon in dioritic 

gneiss ..-...-..-< ea 

Ogden's Hole gneiss . 7 

Oquirrh Mountains 

Palxozoic section ........-..--..--- 
Permo-Carboniferons .--. 

relation of Archzan to later rocks - 

saline hot springs of ....-..--..---- 

Sawmill Caton, Archean of 

Ure h 12) Besscmria hace naacenioaseeo 

PL TISS poses es Saniee ow actete 

Upper Coal Measures ... 

Vermilion Creek group 

Weber quartzite: ...........--..... 

Wahsatch region, Archean topography of ...--..--. 
Humboldt group of...---...--.-- 

Mesozoic shore .......--.-------- 

Seetoya Range 

Wabsatch Station, Vermilion Creek group of -..---- 
Wahweah Mountains, granite in..........--..--.--- 
rhyolite of 

trachyte of....- 

Walker River, Miocene of 
Walker's) lak@-so-s eccense 


hia theory of voleanic 
genesis .......-. 703, 
Wansit's Ridge, Fox Hill Cretaceous ... ae 


Ward de CUiton coccsmeeesosseeen ets 225 
War Eagle Mountain, Idaho, protogenoid granite of. 
Warm Springs thy olitececeaseemsscsnerd= mere en mas 
Warm Spring Valley, infusorial silica of ............ 
palagoniteioti.--- ~~~... --=- 

Warren, General G. K . -2, 427, 
Washakio Basintenccsese. tect cece «vowels oe rieciteine 
Bridger group of ....-.---.-. 396, 397, 

Green River group of...........--- 


- -361, 


Vermilion Creek group of . 


417, 


46 
45, 46 
44 


197 

154, 155 
155 

44 

500 


155 


441 
707, 718 


709, 710 
327 


4 
7 


105 
626, 627 
419 


488, 757 


398, 399 
381 
363, 366 
447, 448 
447 


INDEX. 803 
Page. Page. 
Washoe, propylite .......-..---...--- seesea: 550, 555, 556, 557 | West Humboldt Range, rhyolite of ...............+-. 640 
Watch Hill, basalt cf Triaasicie cscs sac cs aeeoneees 266 
Water-shed, Atlantic and Pacific 85 
Waverly fossils 237, 238 | Wheeler, G. M 490 
Waverly group . 132,177 | Whirlwind Valley, basalt of .. 602 
Dry Cafion 197 | Whitehead Peak, trachyte of .... 582, 583 
East Cation 198 | White Pine Range, Ogden quartzite in 194 
Wovan Oafiont-ctes. 2. seeceee estes 27 Silorian<2-s2-2200 eee eee 188 
Weber Caiion, Devil’s Slide, Jura of...........----- 293 Wahsatch limestone of........-. 205, 206 
Permo-Carboniferous section of. . 163, 164 | White Plains, basalt of..................--.- 675 
S 265 rhyolite of 644, 645 
section, Coal Measures (Upper) of.... 162, 163 White Plains Station, infusorial silica of.....- 421 
Devonian Ogden quartzite of. 157, 158 Miocene limestone of ......- = 422 
Palmozoic .....----seeeeeceee 156,157 | White River divide, Green River group of .......--. 387 
Silurian Ute limestone of ..-. 141 Miocene group ............--......- 353, 408, 451 
Wahsatch limestone of . ..158, 159, 160 Camp Baker, Mcntana....... 408 
Weber quartzite of .....-.160, 161, 162 group of Chalk Blufis.........-- 409 
Weber quartzite, Agate Pass......-..--...---------- 210 Crowi@ree)kseo-s-renccse=aeee 410 
Broa Of Map LViccosetate tence neces 214, 215 MoxtiUnionecasessoccmesesees 409 
Battle Mountain 220, 221 geology of. .... -408, 409, 410 
Bingham Cafion........-. . 213,214 Great Plains... -- 408, 409 
conglomerates in - 149, 217 Owl Creek .2-..-...... 410 
Gonnor|svPeak -2e--o eee eee 214 | White River Valley, Uinta group of ...... ...-...... 406 
(Cortez Ran ger.-2.55.cl2=2---see0% 219 | White Rock Springs, trachyte of..................7. 594 
Cottonwood section ..-. - 216,217 Whitfield, R. P 187, 191, 206, 207, 210, 280, 294 
Gosiute Range .-. 2 PUEOLEE || Wantatoyg Goa D)s Seesosushecseapseeeece 2, 3, 266, 295, 450, 460, 689 
Great Basin .-. : : 919) |mWalliamson, (Majors. .-.----secc<s-ce sr occele sesso 1 
Moleen Cafion..........-.----- OS yvallowaCanonimhyoliteotees--ascss ceases eceeeses cee 636 
Moleen Peak 218 | Willow Creek, Upper Coal Measures of.............- 225 
Ombe Range 215 trachytolol(cescccoccccscc eccceticece 593, 594 
OquilrhsRauges=-sseersee nse eee 213 group, Vermilion Creek group of .-.. 368 
Osino Caiion ... 21g | Winnemucca Lake...-.-.............--..-..--...-. 441 
recapitulation. - 240, 241 change of level ..............--- 505 
résumé ........ 535 MV Olio Olessersisieas ss ecinciacsces 650 
River/Range)------=.2->----- Pree 217 | Witch’s Rocks, Fox Hill Cretaceous 330 
Salt Lake Basin 214 | Woodward, R. W..- 499 
Seetoya Range ............ 219 his determination of zirconium.... 52, 53 
Shoshone Range a PIMLCST) |) Wiebe Ob) ob acoscasnosbosponcoocnesnnedoseecocooboo 420 
Soldier Canon ....- 213 
Tucubits Range 
WEES HESIE® co noseecosenecoo-cece Via palb Oakceeecee cece cman eee ae cecectescer ce ae 141 
Wishkatoht.-= S Reis Plateau, Colorado Cretaceous).---.----<--<.- 315 
z 8 oeceslecenceceeate see teres oe 261 
WGISER CEE BEEEIOA coc Yosemite Valley, granite of 120 
Weber River ..c22 secae cesses osc eyecete<ssacéeseecte ya ace | Te ak aceel eee ae . 
Colorado Cretaceous 
Western America, Eocene of : 
Western Nevada, Jura of .- . 293,294 | Zenobia Peak, Carboniferous of..........--..-...--- 144 
Mesozoic.. 341 | Zircon in dioritic gneiss, Ogden Cation, Wahsatch... 52 
Plioceneiofec~...ca--0 acHeasccosios 440, 441 granite of Humboldt Range .-............. 64 
Western province, Miocene of ....-...-...-.+--.----+ 542 granite of Medicine Bow.......-...-...... 31 
West Humboldt Range, Archean Knotenschiefer.... 86, 87 hornblendic gneiss, Ogden Point, Wahsatch 53 
Archean rocks of .......--- 85 Muscovite schist, Spruce Mountain, Peo- 
Archean sebists in .......-. 86 GPG) Arh so sce socesbec topSosecbeod 5560 58 
Archean schists with minute Zirkel, Prof. Ferdinand ... .547, 550, 551, 564, 569, 580, 591, 599, 
internal corrugations ...-.. 86, 87 601, 604, 605, 613, 639, 647, 650, 656, 
glacier (extinct) of ..-....... 47 657, 666, 669, 672, 675, 682, 719, 722 
muscovite in granitein ..... 86 | Zirkel, Mount, hornblendic schists of ...........-... 38 


END OF VOLUME FIRST. 


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